diff options
Diffstat (limited to 'doc/src/FAQ.html')
| -rw-r--r-- | doc/src/FAQ.html | 837 |
1 files changed, 427 insertions, 410 deletions
diff --git a/doc/src/FAQ.html b/doc/src/FAQ.html index 4285490eeb3..585807e6ab9 100644 --- a/doc/src/FAQ.html +++ b/doc/src/FAQ.html @@ -7,154 +7,152 @@ Frequently Asked Questions (FAQ) for PostgreSQL </H1> <P> -Last updated: Tue Mar 21 16:09:11 EST 2000 +Last updated: Tue Oct 17 00:21:20 EDT 2000 <P> Current maintainer: Bruce Momjian (<A HREF="mailto:pgman@candle.pha.pa.us">pgman@candle.pha.pa.us</A>)<BR><P> -The most recent version of this document can be viewed at the postgreSQL -Web site, <A HREF="http://www.Postgresql.org">http://www.PostgreSQL.org</A>.<P> +The most recent version of this document can be viewed at +<A HREF="http://www.Postgresql.org/docs/faq-english.html"> +http://www.PostgreSQL.org/docs/faq-english.html</A>.<P> -Linux-specific questions are answered in <A -HREF="http://www.PostgreSQL.org/docs/faq-linux.html">http://www.PostgreSQL.org/docs/faq-linux.html</A>.<P> - -Irix-specific questions are answered in <A -HREF="http://www.PostgreSQL.org/docs/faq-irix.html">http://www.PostgreSQL.org/docs/faq-irix.html</A>.<P> - -HPUX-specific questions are answered in <A -HREF="http://www.PostgreSQL.org/docs/faq-hpux.shtml">http://www.PostgreSQL.org/docs/faq-hpux.shtml</A>.<P> +Platform-specific questions are answered at <A +HREF="http://www.PostgreSQL.org/docs/">http://www.PostgreSQL.org/docs/</A>.<P> <HR><P> <H2><CENTER>General Questions</CENTER></H2> -<A HREF="#1.1">1.1</A>) What is PostgreSQL?<BR> -<A HREF="#1.2">1.2</A>) What's the copyright on PostgreSQL?<BR> -<A HREF="#1.3">1.3</A>) What Unix platforms does PostgreSQL run on?<BR> +<A HREF="#1.1">1.1</A>) What is PostgreSQL?<BR> +<A HREF="#1.2">1.2</A>) What's the copyright on PostgreSQL?<BR> +<A HREF="#1.3">1.3</A>) What Unix platforms does PostgreSQL run on?<BR> <A HREF="#1.4">1.4</A>) What non-unix ports are available?<BR> -<A HREF="#1.5">1.5</A>) Where can I get PostgreSQL?<BR> -<A HREF="#1.6">1.6</A>) Where can I get support for PostgreSQL?<BR> -<A HREF="#1.7">1.7</A>) What is the latest release of PostgreSQL?<BR> -<A HREF="#1.8">1.8</A>) What documentation is available for PostgreSQL?<BR> -<A HREF="#1.9">1.9</A>) How do I find out about known bugs or missing features?<BR> -<A HREF="#1.10">1.10</A>) How can I learn SQL?<BR> -<A HREF="#1.11">1.11</A>) Is PostgreSQL Y2K compliant?<BR> -<A HREF="#1.12">1.12</A>) How do I join the development team?<BR> -<A HREF="#1.13">1.13</A>) How do I submit a bug report?<BR> -<A HREF="#1.14">1.14</A>) How does PostgreSQL compare to other DBMS's?<BR> +<A HREF="#1.5">1.5</A>) Where can I get PostgreSQL?<BR> +<A HREF="#1.6">1.6</A>) Where can I get support?<BR> +<A HREF="#1.7">1.7</A>) What is the latest release?<BR> +<A HREF="#1.8">1.8</A>) What documentation is available?<BR> +<A HREF="#1.9">1.9</A>) How do I find out about known bugs or missing features?<BR> +<A HREF="#1.10">1.10</A>) How can I learn SQL?<BR> +<A HREF="#1.11">1.11</A>) Is PostgreSQL Y2K compliant?<BR> +<A HREF="#1.12">1.12</A>) How do I join the development team?<BR> +<A HREF="#1.13">1.13</A>) How do I submit a bug report?<BR> +<A HREF="#1.14">1.14</A>) How does PostgreSQL compare to other DBMS's?<BR> <H2><CENTER>User Client Questions</CENTER></H2> -<A HREF="#2.1">2.1</A>) Are there ODBC drivers for +<A HREF="#2.1">2.1</A>) Are there ODBC drivers for PostgreSQL?<BR> -<A HREF="#2.2">2.2</A>) What tools are available for hooking +<A HREF="#2.2">2.2</A>) What tools are available for hooking PostgreSQL to Web pages?<BR> -<A HREF="#2.3">2.3</A>) Does PostgreSQL have a graphical user interface? +<A HREF="#2.3">2.3</A>) Does PostgreSQL have a graphical user interface? A report generator? An embedded query language interface?<BR> -<A HREF="#2.4">2.4</A>) What languages are available to communicate +<A HREF="#2.4">2.4</A>) What languages are available to communicate with PostgreSQL?<BR> <H2><CENTER>Administrative Questions</CENTER></H2> -<A HREF="#3.1">3.1</A>) Why does initdb fail?<BR> -<A HREF="#3.2">3.2</A>) How do I install PostgreSQL somewhere other than -/usr/local/pgsql?<BR> -<A HREF="#3.3">3.3</A>) When I start the postmaster, I get a +<A HREF="#3.1">3.1</A>) Why does <I>initdb</I> fail?<BR> +<A HREF="#3.2">3.2</A>) How do I install PostgreSQL somewhere other than +<I>/usr/local/pgsql?</I><BR> +<A HREF="#3.3">3.3</A>) When I start the <i>postmaster</i>, I get a <I>Bad System Call</I> or core dumped message. Why?<BR> -<A HREF="#3.4">3.4</A>) When I try to start the postmaster, I get -<I>IpcMemoryCreate</I> errors3. Why?<BR> -<A HREF="#3.5">3.5</A>) When I try to start the postmaster, I get +<A HREF="#3.4">3.4</A>) When I try to start the <i>postmaster</i>, I get +<I>IpcMemoryCreate</I> errors. Why?<BR> +<A HREF="#3.5">3.5</A>) When I try to start the <i>postmaster</i>, I get <I>IpcSemaphoreCreate</I> errors. Why?<BR> -<A HREF="#3.6">3.6</A>) How do I prevent other hosts from accessing my +<A HREF="#3.6">3.6</A>) How do I prevent other hosts from accessing my PostgreSQL database?<BR> -<A HREF="#3.7">3.7</A>) Why can't I connect to my database from +<A HREF="#3.7">3.7</A>) Why can't I connect to my database from another machine?<BR> -<A HREF="#3.8">3.8</A>) Why can't I access the database as the +<A HREF="#3.8">3.8</A>) Why can't I access the database as the <I>root</I> user?<BR> -<A HREF="#3.9">3.9</A>) All my servers crash under concurrent +<A HREF="#3.9">3.9</A>) All my servers crash under concurrent table access. Why?<BR> -<A HREF="#3.10">3.10</A>) How do I tune the database engine for +<A HREF="#3.10">3.10</A>) How do I tune the database engine for better performance?<BR> -<A HREF="#3.11">3.11</A>) What debugging features are available in -PostgreSQL?<BR> -<A HREF="#3.12">3.12</A>) I get 'Sorry, too many clients' when trying to +<A HREF="#3.11">3.11</A>) What debugging features are available?<BR> +<A HREF="#3.12">3.12</A>) I get <I>"Sorry, too many clients"</I> when trying to connect. Why?<BR> -<A HREF="#3.13">3.13</A>) What are the pg_psort.XXX files in my +<A HREF="#3.13">3.13</A>) What are the <I>pg_sorttempNNN.NN</I> files in my database directory?<BR> -<A HREF="#3.14">3.14</A>) How do I set up a pg_group?<BR> <H2><CENTER>Operational Questions</CENTER></H2> -<A HREF="#4.1">4.1</A>) The system seems to be confused about commas, +<A HREF="#4.1">4.1</A>) Why is the system confused about commas, decimal points, and date formats.<BR> -<A HREF="#4.2">4.2</A>) What is the exact difference between +<A HREF="#4.2">4.2</A>) What is the exact difference between binary cursors and normal cursors?<BR> -<A HREF="#4.3">4.3</A>) How do I <I>select</I> only the first few rows of +<A HREF="#4.3">4.3</A>) How do I <small>SELECT</small> only the first few rows of a query?<BR> -<A HREF="#4.4">4.4</A>) How do I get a list of tables, or other +<A HREF="#4.4">4.4</A>) How do I get a list of tables or other things I can see in <I>psql?</I><BR> -<A HREF="#4.5">4.5</A>) How do you remove a column from a table?<BR> +<A HREF="#4.5">4.5</A>) How do you remove a column from a table?<BR> -<A HREF="#4.6">4.6</A>) What is the maximum size for a +<A HREF="#4.6">4.6</A>) What is the maximum size for a row, table, database?<BR> -<A HREF="#4.7">4.7</A>) How much database disk space is required -to store data from a typical flat file?<BR> +<A HREF="#4.7">4.7</A>) How much database disk space is required +to store data from a typical text file?<BR> -<A HREF="#4.8">4.8</A>) How do I find out what indices or +<A HREF="#4.8">4.8</A>) How do I find out what indices or operations are defined in the database?<BR> -<A HREF="#4.9">4.9</A>) My queries are slow or don't make use of the +<A HREF="#4.9">4.9</A>) My queries are slow or don't make use of the indexes. Why?<BR> -<A HREF="#4.10">4.10</A>) How do I see how the query optimizer is +<A HREF="#4.10">4.10</A>) How do I see how the query optimizer is evaluating my query?<BR> -<A HREF="#4.11">4.11</A>) What is an R-tree index?<BR> -<A HREF="#4.12">4.12</A>) What is Genetic Query Optimization?<BR> +<A HREF="#4.11">4.11</A>) What is an R-tree index?<BR> +<A HREF="#4.12">4.12</A>) What is Genetic Query Optimization?<BR> -<A HREF="#4.13">4.13</A>) How do I do regular expression searches -and case-insensitive regexp searching?<BR> -<A HREF="#4.14">4.14</A>) In a query, how do I detect if a field +<A HREF="#4.13">4.13</A>) How do I do regular expression searches +and case-insensitive regular expression searches?<BR> +<A HREF="#4.14">4.14</A>) In a query, how do I detect if a field is NULL?<BR> -<A HREF="#4.15">4.15</A>) What is the difference between the +<A HREF="#4.15">4.15</A>) What is the difference between the various character types?<BR> -<A HREF="#4.16.1">4.16.1</A>) How do I create a serial/auto-incrementing field?<BR> -<A HREF="#4.16.2">4.16.2</A>) How do I get the value of a serial insert?<BR> -<A HREF="#4.16.3">4.16.3</A>) Wouldn't use of currval() and nextval() lead to a race condition with other concurrent backend processes?<BR> - -<A HREF="#4.17">4.17</A>) What is an oid? What is a tid?<BR> -<A HREF="#4.18">4.18</A>) What is the meaning of some of the terms +<A HREF="#4.16.1">4.16.1</A>) How do I create a serial/auto-incrementing field?<BR> +<A HREF="#4.16.2">4.16.2</A>) How do I get the value of a +<small>SERIAL</small> insert?<BR> +<A HREF="#4.16.3">4.16.3</A>) Don't <I>currval()</I> and <I>nextval()</I> lead to a +race condition with other users?<BR> + +<A HREF="#4.17">4.17</A>) What is an <small>OID</small>? What is a +<small>TID</small>?<BR> +<A HREF="#4.18">4.18</A>) What is the meaning of some of the terms used in PostgreSQL?<BR> -<A HREF="#4.19">4.19</A>) Why do I get the error "FATAL: palloc -failure: memory exhausted?"<BR> -<A HREF="#4.20">4.20</A>) How do I tell what PostgreSQL version I +<A HREF="#4.19">4.19</A>) Why do I get the error <I>"FATAL: palloc +failure: memory exhausted?"</I><BR> +<A HREF="#4.20">4.20</A>) How do I tell what PostgreSQL version I am running? <BR> -<A HREF="#4.21">4.21</A>) My large-object operations get <I>invalid +<A HREF="#4.21">4.21</A>) My large-object operations get <I>invalid large obj descriptor.</I> Why?<BR> <A HREF="#4.22">4.22</A>) How do I create a column that will default to the current time?<BR> -<A HREF="#4.23">4.23</A>) Why are my subqueries using <CODE>IN</CODE> so slow?<BR> +<A HREF="#4.23">4.23</A>) Why are my subqueries using +<CODE><small>IN</small></CODE> so slow?<BR> +<A HREF="#4.24">4.24</A>) How do I do an <i>outer</i> join?<BR> <H2><CENTER>Extending PostgreSQL</CENTER></H2> -<A HREF="#5.1">5.1</A>) I wrote a user-defined function. When I run -it in <I>psql,</I> why does it dumps core?<BR> -<A HREF="#5.2">5.2</A>) What does the message: -<I>NOTICE:PortalHeapMemoryFree: 0x402251d0 not in alloc set!</I> mean?<BR> -<A HREF="#5.3">5.3</A>) How can I contribute some nifty new types and functions -for PostgreSQL?<BR> -<A HREF="#5.4">5.4</A>) How do I write a C function to return a +<A HREF="#5.1">5.1</A>) I wrote a user-defined function. When I run +it in <I>psql,</I> why does it dump core?<BR> +<A HREF="#5.2">5.2</A>) What does the message +<I>"NOTICE:PortalHeapMemoryFree: 0x402251d0 not in alloc set!"</I> mean?<BR> +<A HREF="#5.3">5.3</A>) How can I contribute some nifty new types and functions +to PostgreSQL?<BR> +<A HREF="#5.4">5.4</A>) How do I write a C function to return a tuple?<BR> -<A HREF="#5.5">5.5</A>) I have changed a source file. Why does the -recompile does not see the change?<BR> +<A HREF="#5.5">5.5</A>) I have changed a source file. Why does the +recompile not see the change?<BR> <HR> <H2><CENTER>General Questions</CENTER></H2> <H4><A -NAME="1.1">1.1</A>) What is PostgreSQL?</H4><P> +NAME="1.1">1.1</A>) What is PostgreSQL?</H4><P> PostgreSQL is an enhancement of the POSTGRES database management system, a next-generation DBMS research prototype. While PostgreSQL retains the @@ -162,15 +160,15 @@ powerful data model and rich data types of POSTGRES, it replaces the PostQuel query language with an extended subset of SQL. PostgreSQL is free and the complete source is available.<P> -PostgreSQL development is being performed by a team of Internet +PostgreSQL development is performed by a team of Internet developers who all subscribe to the PostgreSQL development mailing list. The current coordinator is Marc G. Fournier (<A -HREF="mailto:scrappy@postgreSQL.org">scrappy@postgreSQL.org</A>). (See -below on how to join). This team is now responsible for all current and -future development of PostgreSQL.<P> +HREF="mailto:scrappy@PostgreSQL.org">scrappy@PostgreSQL.org</A>). (See +below on how to join). This team is now responsible for all development +of PostgreSQL.<P> The authors of PostgreSQL 1.01 were Andrew Yu and Jolly Chen. Many -others have contributed to the porting, testing, debugging and +others have contributed to the porting, testing, debugging, and enhancement of the code. The original Postgres code, from which PostgreSQL is derived, was the effort of many graduate students, undergraduate students, and staff programmers working under the @@ -183,10 +181,10 @@ name was changed at the end of 1996 to PostgreSQL.<P> It is pronounced <I>Post-Gres-Q-L.</I> -<H4><A NAME="1.2">1.2</A>) What's the copyright on +<H4><A NAME="1.2">1.2</A>) What's the copyright on PostgreSQL?</H4><P> -PostgreSQL is subject to the following COPYRIGHT.<P> +PostgreSQL is subject to the following COPYRIGHT:<P> PostgreSQL Data Base Management System<P> @@ -215,7 +213,7 @@ MODIFICATIONS.<P> -<H4><A NAME="1.3">1.3</A>) What Unix platforms does PostgreSQL run +<H4><A NAME="1.3">1.3</A>) What Unix platforms does PostgreSQL run on?</H4><P> The authors have compiled and tested PostgreSQL on the following @@ -243,42 +241,37 @@ platforms (some of these compiles require gcc): </UL> <P> -<H4><A NAME="1.4">1.4</A>) What non-unix ports are available?</H4><P> +<H4><A NAME="1.4">1.4</A>) What non-unix ports are available?</H4><P> -It is possible to compile the libpq C library, psql, and other +It is possible to compile the <I>libpq</I> C library, psql, and other interfaces and binaries to run on MS Windows platforms. In this case, the client is running on MS Windows, and communicates via TCP/IP to a server running on one of our supported Unix platforms.<P> A file <I>win31.mak</I> is included in the distribution for making a -Win32 libpq library and psql.<P> - -The database server is now working on Windows NT using the Cygnus -Unix/NT porting library. See pgsql/doc/README.NT in the distribution.<P> -There is also a web page at <A HREF= -"http://www.freebsd.org/~kevlo/postgres/portNT.html"> -http://www.freebsd.org/~kevlo/postgres/portNT.html.</A> +Win32 <I>libpq</I> library and psql.<P> -There is another port using U/Win at <A HREF= -"http://surya.wipro.com/uwin/ported.html">http://surya.wipro.com/uwin/ported.html.</A> +The database server is now working on Windows NT using Cygwin, the +Cygnus Unix/NT porting library. See <I>pgsql/doc/FAQ_NT</I> in the +distribution. It does not work on MS Windows 9X because Cygwin does not +support the features we need on those platforms. <P> -<H4><A NAME="1.5">1.5</A>) Where can I get PostgreSQL?</H4><P> +<H4><A NAME="1.5">1.5</A>) Where can I get PostgreSQL?</H4><P> The primary anonymous ftp site for PostgreSQL is <A -HREF="ftp://ftp.postgreSQL.org/pub">ftp://ftp.postgreSQL.org/pub</A> -<P> -For mirror sites, see our main web site. +HREF="ftp://ftp.PostgreSQL.org/pub">ftp://ftp.PostgreSQL.org/pub</A>. +For mirror sites, see our main Web site. -<H4><A NAME="1.6">1.6</A>) Where can I get support for PostgreSQL?</H4><P> +<H4><A NAME="1.6">1.6</A>) Where can I get support?</H4><P> -There is no official support for PostgreSQL from the University of +There is no support for PostgreSQL from the University of California, Berkeley. It is maintained through volunteer effort.<P> The main mailing list is: <A -HREF="mailto:pgsql-general@postgreSQL.org">pgsql-general@postgreSQL.org</A>. +HREF="mailto:pgsql-general@PostgreSQL.org">pgsql-general@PostgreSQL.org</A>. It is available for discussion of matters pertaining to PostgreSQL. -To subscribe, send a mail with the lines in the body (not +To subscribe, send mail with the following lines in the body (not the subject line) <PRE> @@ -287,11 +280,11 @@ the subject line) </PRE><P> to <A -HREF="mailto:pgsql-general-request@postgreSQL.org">pgsql-general-request@postgreSQL.org</A>.<P> +HREF="mailto:pgsql-general-request@PostgreSQL.org">pgsql-general-request@PostgreSQL.org</A>.<P> There is also a digest list available. To subscribe to this list, send -email to: <A HREF="mailto:pgsql-general-digest-request@postgreSQL.org"> -pgsql-general-digest-request@postgreSQL.org</A> with a BODY of: +email to: <A HREF="mailto:pgsql-general-digest-request@PostgreSQL.org"> +pgsql-general-digest-request@PostgreSQL.org</A> with a body of: <PRE> subscribe @@ -303,8 +296,8 @@ received around 30k of messages.<P> The bugs mailing list is available. To subscribe to this list, send email to <A -HREF="mailto:bugs-request@postgreSQL.org">bugs-request@postgreSQL.org</A> -with a BODY of:<P> +HREF="mailto:pgsql-bugs-request@PostgreSQL.org">pgsql-bugs-request@PostgreSQL.org</A> +with a body of:<P> <PRE> subscribe @@ -313,8 +306,8 @@ with a BODY of:<P> There is also a developers discussion mailing list available. To subscribe to this list, send email to <A -HREF="mailto:hackers-request@postgreSQL.org">hackers-request@postgreSQL.org</A> -with a BODY of:<P> +HREF="mailto:pgsql-hackers-request@PostgreSQL.org">pgsql-hackers-request@PostgreSQL.org</A> +with a body of:<P> <PRE> subscribe @@ -325,47 +318,54 @@ Additional mailing lists and information about PostgreSQL can be found via the PostgreSQL WWW home page at: <BLOCKQUOTE> -<A HREF="http://postgreSQL.org">http://postgreSQL.org</A> +<A HREF="http://www.PostgreSQL.org">http://www.PostgreSQL.org</A> </BLOCKQUOTE><P> -There is also an IRC channel on EFNet, channel #PostgreSQL. +There is also an IRC channel on EFNet, channel <I>#PostgreSQL.</I> I use the unix command <CODE>irc -c '#PostgreSQL' "$USER" -irc.phoenix.net</CODE><P> +irc.phoenix.net.</CODE><P> Commercial support for PostgreSQL is available at <A -HREF="http://www.pgsql.com">http://www.pgsql.com/</A><P> +HREF="http://www.pgsql.com">http://www.pgsql.com/</A>.<P> -<H4><A NAME="1.7">1.7</A>) What is the latest release of PostgreSQL?</H4><P> +<H4><A NAME="1.7">1.7</A>) What is the latest release?</H4><P> -The latest release of PostgreSQL is version 7.0.<P> +The latest release of PostgreSQL is version 7.0.2.<P> We plan to have major releases every four months.<P> -<H4><A NAME="1.8">1.8</A>) What documentation is available for PostgreSQL?</H4><P> +<H4><A NAME="1.8">1.8</A>) What documentation is available?</H4><P> Several manuals, manual pages, and some small test examples are -included in the distribution. See the /doc directory. You can also -browse the manual on-line at <A -HREF="http://www.postgresql.org/docs/postgres"> -http://www.postgresql.org/docs/postgres.</A> -in the distribution. +included in the distribution. See the <I>/doc</I> directory. You can also +browse the manual online at <A +HREF="http://www.PostgreSQL.org/docs/postgres"> +http://www.PostgreSQL.org/docs/postgres</A>. <P> +There is a PostgreSQL book available at <A +HREF="http://www.PostgreSQL.org/docs/awbook.html"> +http://www.PostgreSQL.org/docs/awbook.html</A>.<P> + <I>psql</I> has some nice \d commands to show information about types, operators, functions, aggregates, etc.<P> -The web site contains even more documentation.<P> +Our Web site contains even more documentation.<P> -<H4><A NAME="1.9">1.9</A>) How do I find out about known bugs or missing features? +<H4><A NAME="1.9">1.9</A>) How do I find out about known bugs or missing features? </H4><P> PostgreSQL supports an extended subset of SQL-92. See our -<A HREF="http://www.postgreSQL.org/docs/todo.html"> -TODO</A> for a list of known bugs, missing features, and future plans.<P> +<A HREF="http://www.PostgreSQL.org/docs/todo.html"> +TODO</A> list for known bugs, missing features, and future plans.<P> + +<H4><A NAME="1.10">1.10</A>) How can I learn SQL?</H4><P> -<H4><A NAME="1.10">1.10</A>) How can I learn SQL?</H4><P> +The PostgreSQL book at <A +HREF="http://www.PostgreSQL.org/docs/awbook.html"> +http://www.PostgreSQL.org/docs/awbook.html</A> teaches SQL. There is a nice tutorial at <A HREF="http://w3.one.net/~jhoffman/sqltut.htm"> @@ -377,40 +377,40 @@ Another one is "Teach Yourself SQL in 21 Days, Second Edition" at <A HREF="http://members.tripod.com/er4ebus/sql/index.htm"> http://members.tripod.com/er4ebus/sql/index.htm </A><P> -Many of our users like <I>The Practical SQL Handbook</I>, Bowman et al., -Addison Wesley. Others like <I>Lan Times Guide to SQL</I>, Groff et al., -Osborne McGraw-Hill.<P> +Many of our users like <I>The Practical SQL Handbook</I>, Bowman, Judith +S., et al., Addison-Wesley. Others like <I>The Complete Reference +SQL</I>, Groff et al., McGraw-Hill.<P> -<H4><A NAME="1.11">1.11</A>) Is PostgreSQL Y2K compliant?</H4><P> +<H4><A NAME="1.11">1.11</A>) Is PostgreSQL Y2K compliant?</H4><P> Yes, we easily handle dates past the year 2000AD, and before 2000BC.<P> -<H4><A NAME="1.12">1.12</A>) How do I join the development team?</H4><P> +<H4><A NAME="1.12">1.12</A>) How do I join the development team?</H4><P> -First, download the latest sources and read the PostgreSQL Developers -documentation on our web site, or in the distribution. -Second, subscribe to the pgsql-hackers and pgsql-patches mailing lists. +First, download the latest source and read the PostgreSQL Developers +documentation on our Web site, or in the distribution. +Second, subscribe to the <I>pgsql-hackers</I> and <I>pgsql-patches</I> mailing lists. Third, submit high-quality patches to pgsql-patches.<P> -There are about a dozen people who have <SMALL>COMMIT</SMALL> privileges to -the PostgreSQL CVS archive. All of them have submitted so many -high-quality patches that it was a pain for the existing +There are about a dozen people who have commit privileges to +the PostgreSQL CVS archive. They each have submitted so many +high-quality patches that it was impossible for the existing committers to keep up, and we had confidence that patches they -committed were likely to be of high quality. +committed were of high quality. -<H4><A NAME="1.13">1.13</A>) How do I submit a bug report?</H4><P> +<H4><A NAME="1.13">1.13</A>) How do I submit a bug report?</H4><P> Fill out the "bug-template" file and send it to: <A -HREF="mailto:bugs@postgreSQL.org">bugs@postgreSQL.org</A><P> +HREF="mailto:pgsql-bugs@PostgreSQL.org">pgsql-bugs@PostgreSQL.org</A><P> Also check out our ftp site <A -HREF="ftp://ftp.postgreSQL.org/pub">ftp://ftp.postgreSQL.org/pub</A> to +HREF="ftp://ftp.PostgreSQL.org/pub">ftp://ftp.PostgreSQL.org/pub</A> to see if there is a more recent PostgreSQL version or patches.<P> -<H4><A NAME="1.14">1.14</A>) How does PostgreSQL compare to other +<H4><A NAME="1.14">1.14</A>) How does PostgreSQL compare to other DBMS's?</H4><P> There are several ways of measuring software: features, performance, @@ -421,11 +421,11 @@ reliability, support, and price.<P> <DD> PostgreSQL has most features present in large commercial DBMS's, like -transactions, subselects, triggers, views, and sophisticated locking. -We have some features they don't have, like user-defined types, -inheritance, rules, and multi-version concurrency control to reduce lock -contention. We don't have foreign key referential integrity or outer -joins, but are working on them for our next release.<BR><BR> +transactions, subselects, triggers, views, foreign key referential +integrity, and sophisticated locking. We have some features they don't +have, like user-defined types, inheritance, rules, and multi-version +concurrency control to reduce lock contention. We don't have outer +joins, but are working on them.<BR><BR> <DT> <B>Performance</B> <DD> @@ -439,15 +439,14 @@ default modes. In <I>no-fsync</I> mode, we are usually faster than commercial databases, though in this mode, an OS crash could cause data corruption. We are working to provide an intermediate mode that suffers less performance overhead than full fsync mode, and will allow data -integrity within 30 seconds of an OS crash. The mode is select-able by -the database administrator.<BR><BR> +integrity within 30 seconds of an OS crash.<BR><BR> In comparison to MySQL or leaner database systems, we are slower on inserts/updates because we have transaction overhead. Of course, MySQL doesn't have any of the features mentioned in the <I>Features</I> section above. We are built for flexibility and features, though we continue to improve performance through profiling and source code -analysis. There is an interesting web page comparing PostgreSQL to MySQL +analysis. There is an interesting Web page comparing PostgreSQL to MySQL at <a href="http://openacs.org/why-not-mysql.html"> http://openacs.org/why-not-mysql.html</a><BR><BR> @@ -484,7 +483,6 @@ add our code to your product with no limitations, except those outlined in our BSD-style license stated above.<BR><BR> </DL> - <HR> <H2><CENTER>User Client Questions</CENTER></H2> @@ -492,13 +490,13 @@ in our BSD-style license stated above.<BR><BR> -<H4><A NAME="2.1">2.1</A>) Are there ODBC drivers for PostgreSQL?</H4><P> +<H4><A NAME="2.1">2.1</A>) Are there ODBC drivers for PostgreSQL?</H4><P> -There are two ODBC drivers available, PostODBC and OpenLink ODBC.<P> +There are two ODBC drivers available, PsqlODBC and OpenLink ODBC.<P> -PostODBC is included in the distribution. More information about it can -be gotten from: <A HREF="http://www.insightdist.com/psqlodbc"> -http://www.insightdist.com/psqlodbc</A><P> +PsqlODBC is included in the distribution. More information about it can +be gotten from <A HREF="ftp://ftp.PostgreSQL.org/pub/odbc/"> +ftp://ftp.PostgreSQL.org/pub/odbc/</A>.<P> OpenLink ODBC can be gotten from <A HREF="http://www.openlinksw.com/"> http://www.openlinksw.com</A>. It works with their standard ODBC client @@ -510,9 +508,11 @@ commercial-quality support, but a freeware version will always be available. Questions to <A HREF="mailto:postgres95@openlink.co.uk">postgres95@openlink.co.uk</A>.<P> +See also the <A HREF="http://www.PostgreSQL.org/docs/programmer/odbc.htm"> +ODBC chapter of the Programmer's Guide</A>.<P> -<H4><A NAME="2.2">2.2</A>) What tools are available for hooking +<H4><A NAME="2.2">2.2</A>) What tools are available for hooking PostgreSQL to Web pages?</H4><P> A nice introduction to Database-backed Web pages can be seen at: <A @@ -521,41 +521,40 @@ HREF="http://www.webtools.com">http://www.webtools.com</A><P> There is also one at <A HREF="http://www.phone.net/home/mwm/hotlist/"> http://www.phone.net/home/mwm/hotlist/.</A><P> -For web integration, PHP is an excellent interface. It is at: +For Web integration, PHP is an excellent interface. It is at <A HREF="http://www.php.net">http://www.php.net</A><P> -PHP is great for simple stuff, but for more complex cases, many -use the perl interface and CGI.pm.<P> +For complex cases, many use the Perl interface and CGI.pm.<P> -A WWW gateway based on WDB using perl can be downloaded from <A +A WWW gateway based on WDB using Perl can be downloaded from <A HREF="http://www.eol.ists.ca/~dunlop/wdb-p95">http://www.eol.ists.ca/~dunlop/wdb-p95</A> -<H4><A NAME="2.3">2.3</A>) Does PostgreSQL have a graphical user interface? +<H4><A NAME="2.3">2.3</A>) Does PostgreSQL have a graphical user interface? A report generator? An embedded query language interface?</H4><P> We have a nice graphical user interface called <I>pgaccess,</I> which is shipped as part of the distribution. <I>Pgaccess</I> also has a report -generator. The web page is <A HREF= +generator. The Web page is <A HREF= "http://www.flex.ro/pgaccess">http://www.flex.ro/pgaccess</A><P> We also include <I>ecpg,</I> which is an embedded SQL query language interface for C. -<H4><A NAME="2.4">2.4</A>) What languages are available to +<H4><A NAME="2.4">2.4</A>) What languages are available to communicate with PostgreSQL?</H4><P> We have: <UL> -<LI>C(libpq) -<LI>C++(libpq++) -<LI>Embedded C(ecpg) -<LI>Java(jdbc) -<LI>Perl(perl5) -<LI>ODBC(odbc) -<LI>Python(PyGreSQL) -<LI>TCL(libpgtcl) -<LI>C Easy API(libpgeasy) -<LI>Embedded HTML(<A HREF="http://www.php.net">PHP from http://www.php.net</A>) +<LI>C (libpq) +<LI>C++ (libpq++) +<LI>Embedded C (ecpg) +<LI>Java (jdbc) +<LI>Perl (perl5) +<LI>ODBC (odbc) +<LI>Python (PyGreSQL) +<LI>TCL (libpgtcl) +<LI>C Easy API (libpgeasy) +<LI>Embedded HTML (<A HREF="http://www.php.net">PHP from http://www.php.net</A>) </UL><P> <HR> @@ -563,50 +562,52 @@ We have: <H2><CENTER>Administrative Questions</CENTER></H2><P> -<H4><A NAME="3.1">3.1</A>) Why does initdb fail?</H4><P> +<H4><A NAME="3.1">3.1</A>) Why does <I>initdb</I> fail?</H4><P> +Try these: <UL> <LI> check that you don't have any of the previous version's binaries in -your path (If you see the message <CODE>WARN:heap_modifytuple: repl is -\ 9</CODE>, this is the problem.) -<Li> check to see that you have the proper paths set +your path +<LI> check to see that you have the proper paths set <LI> check that the <I>postgres</I> user owns the proper files </UL><P> +If you see an error message about <i>oidvector,</i> you definately have +a version mismatch.<P> -<H4><A NAME="3.2">3.2</A>) How do I install PostgreSQL somewhere -other than /usr/local/pgsql?</H4><P> +<H4><A NAME="3.2">3.2</A>) How do I install PostgreSQL somewhere +other than <I>/usr/local/pgsql?</I></H4><P> -The simplest way is to specify the --prefix option when running configure. -If you forgot to do that, you can edit Makefile.global and change POSTGRESDIR -accordingly, or create a Makefile.custom and define POSTGRESDIR there.<P> +The simplest way is to specify the --prefix option when running <I>configure.</I> +If you forgot to do that, you can edit <I>Makefile.global</I> and change POSTGRESDIR +accordingly, or create a <I>Makefile.custom</I> and define POSTGRESDIR there.<P> -<H4><A NAME="3.3">3.3</A>) When I start the postmaster, I get a <I>Bad +<H4><A NAME="3.3">3.3</A>) When I start the <i>postmaster</i>, I get a <I>Bad System Call</I> or core dumped message. Why?</H4><P> It could be a variety of problems, but first check to see that you -have system V extensions installed in your kernel. PostgreSQL requires +have System V extensions installed in your kernel. PostgreSQL requires kernel support for shared memory and semaphores.<P> -<H4><A NAME="3.4">3.4</A>) When I try to start the postmaster, I +<H4><A NAME="3.4">3.4</A>) When I try to start the <i>postmaster,</i> I get <I>IpcMemoryCreate</I> errors. Why?</H4><P> -You either do not have shared memory configured properly in kernel or +You either do not have shared memory configured properly in your kernel or you need to enlarge the shared memory available in the kernel. The exact amount you need depends on your architecture and how many buffers -and backend processes you configure postmaster to run with. +and backend processes you configure for the <i>postmaster.</i> For most systems, with default numbers of buffers and processes, you need a minimum of ~1MB.<P> -<H4><A NAME="3.5">3.5</A>) When I try to start the postmaster, I +<H4><A NAME="3.5">3.5</A>) When I try to start the <i>postmaster,</i> I get <I>IpcSemaphoreCreate</I> errors. Why?</H4><P> If the error message is <I>IpcSemaphoreCreate: semget failed (No space left on device)</I> then your kernel is not configured with enough semaphores. Postgres needs one semaphore per potential backend process. -A temporary solution is to start the postmaster with a smaller limit on +A temporary solution is to start the <i>postmaster</i> with a smaller limit on the number of backend processes. Use <I>-N</I> with a parameter less than the default of 32. A more permanent solution is to increase your kernel's <SMALL>SEMMNS</SMALL> and <SMALL>SEMMNI</SMALL> parameters.<P> @@ -615,43 +616,42 @@ If the error message is something else, you might not have semaphore support configured in your kernel at all.<P> -<H4><A NAME="3.6">3.6</A>) How do I prevent other hosts from +<H4><A NAME="3.6">3.6</A>) How do I prevent other hosts from accessing my PostgreSQL database?</H4><P> By default, PostgreSQL only allows connections from the local machine -using unix domain sockets. Other machines will not be able to connect +using Unix domain sockets. Other machines will not be able to connect unless you add the <I>-i</I> flag to the <I>postmaster,</I> <B>and</B> enable host-based authentication by modifying the file <I>$PGDATA/pg_hba.conf</I> accordingly. This will allow TCP/IP connections. <P> -<H4><A NAME="3.7">3.7</A>) Why can't I connect to my database from +<H4><A NAME="3.7">3.7</A>) Why can't I connect to my database from another machine?</H4><P> The default configuration allows only unix domain socket connections from the local machine. To enable TCP/IP connections, make sure the -postmaster has been started with the <I>-i</I> option, and add an +<i>postmaster</i> has been started with the <I>-i</I> option, and add an appropriate host entry to the file -<I>pgsql/data/pg_hba.conf</I>. See the <I>pg_hba.conf</I> manual page.<P> +<I>pgsql/data/pg_hba.conf</I>. - -<H4><A NAME="3.8">3.8</A>) Why can't I access the database as the <I>root</I> +<H4><A NAME="3.8">3.8</A>) Why can't I access the database as the <I>root</I> user?</H4><P> You should not create database users with user id 0 (root). They will be -unable to access the database. This is a security precaution because -of the ability of any user to dynamically link object modules into the +unable to access the database. This is a security precaution because +of the ability of users to dynamically link object modules into the database engine.<P> -<H4><A NAME="3.9">3.9</A>) All my servers crash under concurrent +<H4><A NAME="3.9">3.9</A>) All my servers crash under concurrent table access. Why?</H4><P> This problem can be caused by a kernel that is not configured to support semaphores.<P> -<H4><A NAME="3.10">3.10</A>) How do I tune the database engine for +<H4><A NAME="3.10">3.10</A>) How do I tune the database engine for better performance?</H4><P> Certainly, indices can speed up queries. The <SMALL>EXPLAIN</SMALL> command @@ -659,7 +659,7 @@ allows you to see how PostgreSQL is interpreting your query, and which indices are being used.<P> If you are doing a lot of <SMALL>INSERTs</SMALL>, consider doing them in a large -batch using the <SMALL>COPY</SMALL> command. This is much faster than single +batch using the <SMALL>COPY</SMALL> command. This is much faster than individual <SMALL>INSERTS.</SMALL> Second, statements not in a <SMALL>BEGIN WORK/COMMIT</SMALL> transaction block are considered to be in their own transaction. Consider performing several statements in a single @@ -667,36 +667,36 @@ transaction block. This reduces the transaction overhead. Also consider dropping and recreating indices when making large data changes.<P> -There are several tuning things that can be done. You can disable -fsync() by starting the postmaster with a <I>-o -F</I> option. This will -prevent <I>fsync()'s</I> from flushing to disk after every transaction.<P> +There are several tuning options. You can disable +<I>fsync()</I> by starting the <I>postmaster</I> with a <I>-o -F</I> +option. This will prevent <I>fsync()'s</I> from flushing to disk after +every transaction.<P> -You can also use the postmaster -B option to increase the number of +You can also use the <I>postmaster</I> <I>-B</I> option to increase the number of shared memory buffers used by the backend processes. If you make this -parameter too high, the postmaster may not start up because you've exceeded +parameter too high, the <I>postmaster</I> may not start because you've exceeded your kernel's limit on shared memory space. Each buffer is 8K and the default is 64 buffers.<P> -You can also use the backend -S option to increase the maximum amount -of memory used by the backend process for temporary sorts. The -S value +You can also use the backend <I>-S</I> option to increase the maximum amount +of memory used by the backend process for temporary sorts. The <I>-S</I> value is measured in kilobytes, and the default is 512 (ie, 512K).<P> -You can also use the <SMALL>CLUSTER</SMALL> command to group data in base tables to -match an index. See the cluster(l) manual page for more details.<P> +You can also use the <SMALL>CLUSTER</SMALL> command to group data in tables to +match an index. See the <small>CLUSTER</small> manual page for more details.<P> -<H4><A NAME="3.11">3.11</A>) What debugging features are available in -PostgreSQL?</H4><P> +<H4><A NAME="3.11">3.11</A>) What debugging features are available?</H4><P> PostgreSQL has several features that report status information that can be valuable for debugging purposes.<P> -First, by running configure with the --enable-cassert option, many +First, by running <I>configure</I> with the --enable-cassert option, many <I>assert()'s</I> monitor the progress of the backend and halt the program when something unexpected occurs.<P> -Both postmaster and postgres have several debug options available. -First, whenever you start the postmaster, make sure you send the +Both <I>postmaster</I> and <I>postgres</I> have several debug options available. +First, whenever you start the <I>postmaster,</I> make sure you send the standard output and error to a log file, like: <PRE> cd /usr/local/pgsql @@ -705,122 +705,102 @@ standard output and error to a log file, like: This will put a server.log file in the top-level PostgreSQL directory. This file contains useful information about problems or errors -encountered by the server. Postmaster has a -d option that allows even -more detailed information to be reported. The -d option takes a number +encountered by the server. <I>Postmaster</I> has a <I>-d</I> option that allows even +more detailed information to be reported. The <I>-d</I> option takes a number that specifies the debug level. Be warned that high debug level values generate large log files.<P> -You can actually run the postgres backend from the command line, and -type your SQL statement directly. This is recommended <B>only</B> for -debugging purposes. Note that a newline terminates the query, not a -semicolon. If you have compiled with debugging symbols, you can use a -debugger to see what is happening. Because the backend was not started -from the postmaster, it is not running in an identical environment and -locking/backend interaction problems may not be duplicated. Some -debuggers can attach to an already-running backend; that is the most -convenient way to diagnose problems in the normal multi-backend -environment. -<P> - -The postgres program has -s, -A, and -t options that can be very useful +If the <i>postmaster</i> is not running, you can actually run the +<I>postgres</I> backend from the command line, and type your SQL statement +directly. This is recommended <B>only</B> for debugging purposes. Note +that a newline terminates the query, not a semicolon. If you have +compiled with debugging symbols, you can use a debugger to see what is +happening. Because the backend was not started from the <I>postmaster,</I> it +is not running in an identical environment and locking/backend +interaction problems may not be duplicated.<P> + +If the <i>postmaster</i> is running, start <I>psql</I> in one window, +then find the <small>PID</small> of the <i>postgres</i> process used by +<i>psql.</i> Use a debugger to attach to the <i>postgres</i> +<small>PID.</small> You can set breakpoints in the debugger and issue +queries from <i>psql.</i> If you are debugging <i>postgres</i> startup, +you can set PGOPTIONS="-W n", then start <i>psql.</i> This will cause +startup to delay for <i>n</i> seconds so you can attach with the +debugger and trace through the startup sequence.<P> + +The <I>postgres</I> program has <I>-s, -A,</I> and <I>-t</I> options that can be very useful for debugging and performance measurements.<P> You can also compile with profiling to see what functions are taking execution time. The backend profile files will be deposited in the -pgsql/data/base/dbname directory. The client profile file will be put +<I>pgsql/data/base/dbname</I> directory. The client profile file will be put in the client's current directory.<P> <H4><A NAME="3.12">3.12</A>) I get 'Sorry, too many clients' when trying to connect. Why?</H4><P> -You need to increase the postmaster's limit on how many concurrent backend +You need to increase the <i>postmaster's</i> limit on how many concurrent backend processes it can start.<P> -In Postgres 6.5 and up, the default limit is 32 processes. You can -increase it by restarting the postmaster with a suitable <I>-N</I> +In PostgreSQL 6.5 and up, the default limit is 32 processes. You can +increase it by restarting the <i>postmaster</i> with a suitable <I>-N</I> value. With the default configuration you can set <I>-N</I> as large as -1024; if you need more, increase <SMALL>MAXBACKENDS</SMALL> in +1024. If you need more, increase <SMALL>MAXBACKENDS</SMALL> in <I>include/config.h</I> and rebuild. You can set the default value of -<I>-N</I> at configuration time, if you like, using configure's +<I>-N</I> at configuration time, if you like, using <I>configure's</I> <I>--with-maxbackends</I> switch.<P> Note that if you make <I>-N</I> larger than 32, you must also increase -<I>-B</I> beyond its default of 64; -B must be at least twice -N, and +<I>-B</I> beyond its default of 64; <I>-B</I> must be at least twice <I>-N,</I> and probably should be more than that for best performance. For large numbers of backend processes, you are also likely to find that you need to increase various Unix kernel configuration parameters. Things to check include the maximum size of shared memory blocks, -<SMALL>SHMMAX,</SMALL> the maximum number of semaphores, -<SMALL>SEMMNS</SMALL> and <SMALL>SEMMNI,</SMALL> the maximum number of -processes, <SMALL>NPROC,</SMALL> the maximum number of processes per -user, <SMALL>MAXUPRC,</SMALL> and the maximum number of open files, -<SMALL>NFILE</SMALL> and <SMALL>NINODE.</SMALL> The reason that Postgres -has a limit on the number of allowed backend processes is so that you -can ensure that your system won't run out of resources.<P> - -In Postgres versions prior to 6.5, the maximum number of backends was +<SMALL>SHMMAX;</SMALL> the maximum number of semaphores, +<SMALL>SEMMNS</SMALL> and <SMALL>SEMMNI;</SMALL> the maximum number of +processes, <SMALL>NPROC;</SMALL> the maximum number of processes per +user, <SMALL>MAXUPRC;</SMALL> and the maximum number of open files, +<SMALL>NFILE</SMALL> and <SMALL>NINODE.</SMALL> The reason that PostgreSQL +has a limit on the number of allowed backend processes is so +your system won't run out of resources.<P> + +In PostgreSQL versions prior to 6.5, the maximum number of backends was 64, and changing it required a rebuild after altering the MaxBackendId constant in <I>include/storage/sinvaladt.h.</I><P> -<H4><A NAME="3.13">3.13</A>) What are the pg_tempNNN.NN files in my +<H4><A NAME="3.13">3.13</A>) What are the <I>pg_sorttempNNN.NN</I> files in my database directory?</H4><P> They are temporary files generated by the query executor. For example, if a sort needs to be done to satisfy an <SMALL>ORDER BY,</SMALL> and -the sort requires more space than the backend's -S parameter allows, -then temp files are created to hold the extra data.<P> +the sort requires more space than the backend's <I>-S</I> parameter allows, +then temporary files are created to hold the extra data.<P> -The temp files should go away automatically, but might not if a backend -crashes during a sort. If you have no transactions running at the time, +The temporary files should be deleted automatically, but might not if a backend +crashes during a sort. If you have no backends running at the time, it is safe to delete the pg_tempNNN.NN files.<P> -<H4><A NAME="3.14">3.14</A>) How do I set up a pg_group?</H4><P> - -Currently, there is no easy interface to set up user groups. You have to -explicitly insert/update the pg_group table. For example: - -<PRE> - jolly=> insert into pg_group (groname, grosysid, grolist) - jolly=> values ('posthackers', '1234', '{5443, 8261}'); - INSERT 548224 - jolly=> grant insert on foo to group posthackers; - CHANGE - jolly=> -</PRE><P> - - The fields in pg_group are: -<UL> -<LI>groname: the group name. This a name and should -be purely alphanumeric. Do not include underscores -or other punctuation. -<LI>grosysid: the group id. This is an int4. -This should be unique for each group. -<LI>grolist: the list of pg_user id's that belong in the group. -This is an int4[]. -</UL><P> - - <HR> <H2><CENTER>Operational Questions</CENTER></H2><P> -<H4><A NAME="4.1">4.1</A>) The system seems to be confused about +<H4><A NAME="4.1">4.1</A>) Why is system confused about commas, decimal points, and date formats.</H4><P> -Check your locale configuration. PostgreSQL uses the locale settings of -the user that ran the postmaster process. There are postgres and psql +Check your locale configuration. PostgreSQL uses the locale setting of +the user that ran the <i>postmaster</i> process. There are postgres and psql SET commands to control the date format. Set those accordingly for your operating environment.<P> -<H4><A NAME="4.2">4.2</A>) What is the exact difference between +<H4><A NAME="4.2">4.2</A>) What is the exact difference between binary cursors and normal cursors?</H4><P> See the <SMALL>DECLARE</SMALL> manual page for a description.<P> -<H4><A NAME="4.3">4.3</A>) How do I <SMALL>SELECT</SMALL> only the first few +<H4><A NAME="4.3">4.3</A>) How do I <SMALL>SELECT</SMALL> only the first few rows of a query?</H4><P> See the <SMALL>FETCH</SMALL> manual page, or use SELECT ... LIMIT....<P> @@ -832,17 +812,17 @@ PostgreSQL may be able to evaluate only the first few records requested, or the entire query may have to be evaluated until the desired rows have been generated.<P> -<H4><A NAME="4.4">4.4</A>) How do I get a list of tables, or other -information I see in <I>psql?</I><BR></H4><P> +<H4><A NAME="4.4">4.4</A>) How do I get a list of tables or other +things I can see in <I>psql?</I><BR></H4><P> -You can read the source code for <I>psql,</I> file -pgsql/src/bin/psql/psql.c. It contains SQL commands that generate the +You can read the source code for <I>psql</I> in file +<I>pgsql/src/bin/psql/psql.c.</I> It contains SQL commands that generate the output for psql's backslash commands. You can also start <I>psql</I> -with the <I>-E</I> option so that it will print out the queries it uses +with the <I>-E</I> option so it will print out the queries it uses to execute the commands you give.<P> -<H4><A NAME="4.5">4.5</A>) How do you remove a column from a +<H4><A NAME="4.5">4.5</A>) How do you remove a column from a table?</H4><P> We do not support <SMALL>ALTER TABLE DROP COLUMN,</SMALL> but do @@ -858,23 +838,34 @@ this: -<H4><A NAME="4.6">4.6</A>) What is the maximum size for a +<H4><A NAME="4.6">4.6</A>) What is the maximum size for a row, table, database?</H4><P> -Rows are limited to 8K bytes, but this can be changed by editing -<I>include/config.h</I> and changing <SMALL>BLCKSZ.</SMALL> To use attributes -larger than 8K, you can also use the large object interface.<P> +These are the limits: + +<PRE> +Maximum size for a database? unlimited (60GB databases exist) +Maximum size for a table? unlimited on all operating systems +Maximum size for a row? 8k, configurable to 32k +Maximum number of rows in a table? unlimited +Maximum number of columns in a table? unlimited +Maximum number of indexes on a table? unlimited +</PRE> + +Of course, these are not actually unlimited, but limited to available +disk space.<P> -Rows do not cross 8k boundaries so a 5k row will require 8k of -storage.<P> +To change the maximum row size, edit <I>include/config.h</I> and change +<SMALL>BLCKSZ.</SMALL> To use attributes larger than 8K, you can also +use the large object interface.<P> -Table and database sizes are unlimited. There are many databases that -are tens of gigabytes, and probably some that are hundreds. +The row length limit will be removed in 7.1.<P> -<H4><A NAME="4.7">4.7</A>)How much database disk space is required to -store data from a typical flat file?<BR></H4><P> -A Postgres database can require about six and a half times the disk space +<H4><A NAME="4.7">4.7</A>) How much database disk space is required to +store data from a typical text file?<BR></H4><P> + +A PostgreSQL database may need six-and-a-half times the disk space required to store the data in a flat file.<P> Consider a file of 300,000 lines with two integers on each line. The @@ -901,10 +892,10 @@ this data can be estimated at 14MB: 1755 database pages * 8192 bytes per page = 14,376,960 bytes (14MB) </PRE></P> -Indexes do not contain as much overhead, but do contain the data that is +Indexes do not require as much overhead, but do contain the data that is being indexed, so they can be large also.<P> -<H4><A NAME="4.8">4.8</A>) How do I find out what indices or +<H4><A NAME="4.8">4.8</A>) How do I find out what indices or operations are defined in the database?</H4><P> <I>psql</I> has a variety of backslash commands to show such information. Use @@ -915,11 +906,11 @@ illustrates many of the <SMALL>SELECT</SMALL>s needed to get information from the database system tables.<P> -<H4><A NAME="4.9">4.9</A>) My queries are slow or don't make +<H4><A NAME="4.9">4.9</A>) My queries are slow or don't make use of the indexes. Why?</H4><P> -PostgreSQL does not automatically maintain statistics. One has to make -an explicit <SMALL>VACUUM</SMALL> call to update the statistics. After +PostgreSQL does not automatically maintain statistics. V<SMALL>ACUUM</SMALL> +must be run to update the statistics. After statistics are updated, the optimizer knows how many rows in the table, and can better decide if it should use indices. Note that the optimizer does not use indices in cases when the table is small because a @@ -927,7 +918,7 @@ sequential scan would be faster.<P> For column-specific optimization statistics, use <SMALL>VACUUM ANALYZE.</SMALL> <SMALL>VACUUM ANALYZE</SMALL> is important for complex -multi-join queries, so the optimizer can estimate the number of rows +multijoin queries, so the optimizer can estimate the number of rows returned from each table, and choose the proper join order. The backend does not keep track of column statistics on its own, so <SMALL>VACUUM ANALYZE</SMALL> must be run to collect them periodically.<P> @@ -943,64 +934,60 @@ the string. So, to use indices, <SMALL>LIKE</SMALL> searches should not begin with <I>%,</I> and <I>~</I>(regular expression searches) should start with <I>^.</I> -<H4><A NAME="4.10">4.10</A>) How do I see how the query optimizer is +<H4><A NAME="4.10">4.10</A>) How do I see how the query optimizer is evaluating my query?</H4><P> See the <SMALL>EXPLAIN</SMALL> manual page.<P> -<H4><A NAME="4.11">4.11</A>) What is an R-tree index?</H4><P> +<H4><A NAME="4.11">4.11</A>) What is an R-tree index?</H4><P> -An r-tree index is used for indexing spatial data. A hash index can't +An R-tree index is used for indexing spatial data. A hash index can't handle range searches. A B-tree index only handles range searches in a single dimension. R-tree's can handle multi-dimensional data. For example, if an R-tree index can be built on an attribute of type <I>point,</I> -the system can more efficient answer queries like select all points -within a bounding rectangle.<P> +the system can more efficiently answer queries such as "select all points +within a bounding rectangle."<P> -The canonical paper that describes the original R-Tree design is:<P> +The canonical paper that describes the original R-tree design is:<P> -Guttman, A. "R-Trees: A Dynamic Index Structure for Spatial Searching." +Guttman, A. "R-trees: A Dynamic Index Structure for Spatial Searching." Proc of the 1984 ACM SIGMOD Int'l Conf on Mgmt of Data, 45-57.<P> You can also find this paper in Stonebraker's "Readings in Database -Systems"<P> +Systems".<P> -Builtin R-Trees can handle polygons and boxes. In theory, R-trees can +Built-in R-trees can handle polygons and boxes. In theory, R-trees can be extended to handle higher number of dimensions. In practice, -extending R-trees require a bit of work and we don't currently have any +extending R-trees requires a bit of work and we don't currently have any documentation on how to do it.<P> -<H4><A NAME="4.12">4.12</A>) What is Genetic Query +<H4><A NAME="4.12">4.12</A>) What is Genetic Query Optimization?</H4><P> -The GEQO module in PostgreSQL is intended to solve the query -optimization problem of joining many tables by means of a Genetic +The GEQO module speeds query +optimization when joining many tables by means of a Genetic Algorithm (GA). It allows the handling of large join queries through -non-exhaustive search.<P> - -For further information see the documentation. - +nonexhaustive search.<P> +<H4><A NAME="4.13">4.13</A>) How do I do regular expression searches and +case-insensitive regular expression searches?</H4><P> -<H4><A NAME="4.13">4.13</A>) How do I do regular expression searches and -case-insensitive regexp searching?</H4><P> - -The <I>~</I> operator does regular-expression matching, and <I>~*</I> -does case-insensitive regular-expression matching. There is no +The <I>~</I> operator does regular expression matching, and <I>~*</I> +does case-insensitive regular expression matching. There is no case-insensitive variant of the LIKE operator, but you can get the effect of case-insensitive <SMALL>LIKE</SMALL> with this: <PRE> WHERE lower(textfield) LIKE lower(pattern) </PRE> -<H4><A NAME="4.14">4.14</A>) In a query, how do I detect if a field +<H4><A NAME="4.14">4.14</A>) In a query, how do I detect if a field is NULL?</H4><P> You test the column with IS NULL and IS NOT NULL.<P> -<H4><A NAME="4.15">4.15</A>) What is the difference between the +<H4><A NAME="4.15">4.15</A>) What is the difference between the various character types?</H4> <PRE> @@ -1016,7 +1003,7 @@ BYTEA bytea variable-length array of bytes You will see the internal name when examining system catalogs and in some error messages.<P> -The last four types above are "varlena" types (i.e. the first four bytes +The last four types above are "varlena" types (i.e., the first four bytes are the length, followed by the data). <I>char(#)</I> allocates the maximum number of bytes no matter how much data is stored in the field. <I>text, varchar(#),</I> and <I>bytea</I> all have variable length on the disk, @@ -1025,18 +1012,18 @@ them. Specifically, the penalty is for access to all columns after the first column of this type.<P> -<H4><A NAME="4.16.1">4.16.1</A>) How do I create a +<H4><A NAME="4.16.1">4.16.1</A>) How do I create a serial/auto-incrementing field?</H4><P> -PostgreSQL supports <SMALL>SERIAL</SMALL> data type. It auto-creates a -sequence and index on the column. For example, this... +PostgreSQL supports a <SMALL>SERIAL</SMALL> data type. It auto-creates a +sequence and index on the column. For example, this: <PRE> CREATE TABLE person ( id SERIAL, name TEXT ); </PRE> -...is automatically translated into this... +is automatically translated into this: <PRE> CREATE SEQUENCE person_id_seq; CREATE TABLE person ( @@ -1047,56 +1034,72 @@ sequence and index on the column. For example, this... </PRE> See the <I>create_sequence</I> manual page for more information about sequences. -You can also use each row's <I>oid</I> field as a unique value. However, if +You can also use each row's <I>OID</I> field as a unique value. However, if you need to dump and reload the database, you need to use <I>pg_dump's -o</I> -option or <SMALL>COPY WITH OIDS</SMALL> option to preserve the oids.<P> +option or <SMALL>COPY WITH OIDS</SMALL> option to preserve the <small>OID</small>s.<P> -For more details, see Bruce Momjian's chapter on -<A HREF="http://www.postgresql.org/docs/aw_pgsql_book/node74.html">Numbering Rows.</A> +<A HREF="http://www.PostgreSQL.org/docs/aw_pgsql_book">Numbering Rows.</A> -<H4><A NAME="4.16.2">4.16.2</A>) How do I get the back the generated SERIAL value after an insert?</H4><P> -Probably the simplest approach is to to retrieve the next SERIAL value from the sequence object with the <I>nextval()</I> function <I>before</I> inserting and then insert it explicitly. Using the example table in <A HREF="#4.16.1">4.16.1</A>, that might look like this: +<H4><A NAME="4.16.2">4.16.2</A>) How do I get the value of a +<small>SERIAL</small> insert?</H4><P> +One approach is to to retrieve the next SERIAL value from the sequence object with the <I>nextval()</I> function <I>before</I> inserting and then insert it explicitly. Using the example table in <A HREF="#4.16.1">4.16.1</A>, that might look like this: <PRE> $newSerialID = nextval('person_id_seq'); INSERT INTO person (id, name) VALUES ($newSerialID, 'Blaise Pascal'); </PRE> -You would then also have the new value stored in <CODE>$newSerialID</CODE> for use in other queries (e.g., as a foreign key to the <CODE>person</CODE> table). Note that the name of the automatically-created SEQUENCE object will be named <<I>table</I>>_<<I>serialcolumn</I>>_<I>seq</I>, where <I>table</I> and <I>serialcolumn</I> are the names of your table and your SERIAL column, respectively. + +You would then also have the new value stored in +<CODE>$newSerialID</CODE> for use in other queries (e.g., as a foreign +key to the <CODE>person</CODE> table). Note that the name of the +automatically created SEQUENCE object will be named +<<I>table</I>>_<<I>serialcolumn</I>>_<I>seq</I>, where +<I>table</I> and <I>serialcolumn</I> are the names of your table and +your SERIAL column, respectively. + <P> -Similarly, you could retrieve the just-assigned SERIAL value with the <I>currval</I>() function <I>after</I> it was inserted by default, e.g., +Alternatively, you could retrieve the assigned SERIAL value with the <I>currval</I>() function <I>after</I> it was inserted by default, e.g., <PRE> INSERT INTO person (name) VALUES ('Blaise Pascal'); $newID = currval('person_id_seq'); </PRE> -Finally, you could use the <A HREF="#4.17">oid</A> returned from the INSERT statement to lookup the default value, though this is probably the least portable approach. In perl, using DBI with Edmund Mergl's DBD::Pg module, the oid value is made available via $sth->{pg_oid_status} after $sth->execute(). -<H4><A NAME="4.16.3">4.16.3</A>) Wouldn't use of currval() and nextval() lead to a race condition with other concurrent backend processes?</H4><P> +Finally, you could use the <A HREF="#4.17"><small>OID</small></A> +returned from the INSERT statement to look up the default value, though +this is probably the least portable approach. In Perl, using DBI with +Edmund Mergl's DBD::Pg module, the oid value is made available via +<I>$sth->{pg_oid_status} after $sth->execute().</I> + +<H4><A NAME="4.16.3">4.16.3</A>) Don't <I>currval()</I> and <I>nextval()</I> lead to +a race condition with other users?</H4><P> -No. That has been handled by the backends. +No. This is handled by the backends. -<H4><A NAME="4.17">4.17</A>) What is an oid? What is a tid?</H4><P> +<H4><A NAME="4.17">4.17</A>) What is an <small>OID</small>? What is a +<small>TID</small>?</H4><P> -Oids are PostgreSQL's answer to unique row ids. Every row that is -created in PostgreSQL gets a unique oid. All oids generated during -initdb are less than 16384 (from <I>backend/access/transam.h</I>). All -user-created oids are equal or greater that this. By default, all these -oids are unique not only within a table, or database, but unique within -the entire PostgreSQL installation.<P> +<small>OID</small>s are PostgreSQL's answer to unique row ids. Every +row that is created in PostgreSQL gets a unique <small>OID</small>. All +<small>OID</small>s generated during <I>initdb</I> are less than 16384 +(from <I>backend/access/transam.h</I>). All user-created +<small>OID</small>s are equal to or greater than this. By default, all +these <small>OID</small>s are unique not only within a table or +database, but unique within the entire PostgreSQL installation.<P> -PostgreSQL uses oids in its internal system tables to link rows between -tables. These oids can be used to identify specific user rows and used -in joins. It is recommended you use column type oid to store oid -values. See the <I>sql(l)</I> manual page to see the other internal columns. -You can create an index on the oid field for faster access.<P> +PostgreSQL uses <small>OID</small>s in its internal system tables to link rows between +tables. These <small>OID</small>s can be used to identify specific user rows and used +in joins. It is recommended you use column type <small>OID</small> to +store <small>OID</small> +values. You can create an index on the <small>OID</small> field for faster access.<P> -Oids are assigned to all new rows from a central area that is used by -all databases. If you want to change the oid to something else, or if -you want to make a copy of the table, with the original oid's, there is +O<small>id</small>s are assigned to all new rows from a central area that is used by +all databases. If you want to change the <small>OID</small> to something else, or if +you want to make a copy of the table, with the original <small>OID</small>'s, there is no reason you can't do it: <PRE> CREATE TABLE new_table(old_oid oid, mycol int); - SELECT INTO new SELECT old_oid, mycol FROM old; + SELECT old_oid, mycol INTO new FROM old; COPY new TO '/tmp/pgtable'; DELETE FROM new; COPY new WITH OIDS FROM '/tmp/pgtable'; @@ -1106,12 +1109,16 @@ no reason you can't do it: --> </PRE><P> -Tids are used to identify specific physical rows with block and offset +O<small>ID</small>s are stored as 4-byte integers, and will overflow +at 4 billion. No one has reported this ever happening, and we plan to +have the limit removed before anyone does.<P> + +T<small>ID</small>s are used to identify specific physical rows with block and offset values. Tids change after rows are modified or reloaded. They are used by index entries to point to physical rows.<P> -<H4><A NAME="4.18">4.18</A>) What is the meaning of some of the terms +<H4><A NAME="4.18">4.18</A>) What is the meaning of some of the terms used in PostgreSQL?</H4><P> Some of the source code and older documentation use terms that have more @@ -1124,17 +1131,21 @@ common usage. Here are some: <LI> retrieve, select <LI> replace, update <LI> append, insert -<LI> oid, serial value +<LI> <small>OID</small>, serial value <LI> portal, cursor <LI> range variable, table name, table alias </UL><P> -<H4><A NAME="4.19">4.19</A>) Why do I get the error "FATAL: palloc -failure: memory exhausted?"<BR></H4><P> +A list of general database terms can be found at: <a +href="http://www.comptechnews.com/~reaster/dbdesign.html"> +http://www.comptechnews.com/~reaster/dbdesign.html</a><P> + +<H4><A NAME="4.19">4.19</A>) Why do I get the error <I>"FATAL: palloc +failure: memory exhausted?"</I><BR></H4><P> It is possible you have run out of virtual memory on your system, or your kernel has a low limit for certain resources. Try this before -starting the postmaster: +starting the <i>postmaster:</i> <PRE> ulimit -d 65536 @@ -1160,34 +1171,27 @@ You need to put <CODE>BEGIN WORK</CODE> and <CODE>COMMIT </CODE> around any use of a large object handle, that is, surrounding <CODE>lo_open</CODE> ... <CODE>lo_close.</CODE><P> -Current PostgreSQL enforces the rule by closing large object handles at -transaction commit, which will be instantly upon completion of the -<I>lo_open</I> command if you are not inside a transaction. So the -first attempt to do anything with the handle will draw <I>invalid large -obj descriptor.</I> So code that used to work (at least most of the -time) will now generate that error message if you fail to use a -transaction.<P> +Currently PostgreSQL enforces the rule by closing large object handles +at transaction commit. So the first attempt to do anything with the +handle will draw <I>invalid large obj descriptor.</I> So code that used +to work (at least most of the time) will now generate that error message +if you fail to use a transaction.<P> If you are using a client interface like ODBC you may need to set <CODE>auto-commit off.</CODE><P> <H4><A NAME="4.22">4.22</A>) How do I create a column that will default to the current time?<BR></H4><P> -This way always works: -<CODE><PRE> - CREATE TABLE test (x int, modtime timestamp default now() ); -</PRE></CODE> -In releases 7.0 and later, you may use: +Use <i>now()</i>: <CODE><PRE> - create table test (x int, modtime timestamp default 'now'); + CREATE TABLE test (x int, modtime timestamp DEFAULT now() ); </PRE></CODE> <P> -<H4><A NAME="4.23">4.23</A>) Why are my subqueries using <CODE>IN</CODE> so -slow?<BR></H4><P> -Currently, we join subqueries to outer queries by sequential scanning +<H4><A NAME="4.23">4.23</A>) Why are my subqueries using +<CODE><small>IN</small></CODE> so slow?<BR></H4><P> +Currently, we join subqueries to outer queries by sequentially scanning the result of the subquery for each row of the outer query. A workaround -is to replace <CODE>IN</CODE> with <CODE>EXISTS</CODE>. For example, -change: +is to replace <CODE>IN</CODE> with <CODE>EXISTS</CODE>: <CODE><PRE> SELECT * FROM tab @@ -1201,48 +1205,61 @@ to: </PRE></CODE> We hope to fix this limitation in a future release. +<H4><A NAME="4.24">4.24</A>) How do I do an <i>outer</i> join?<BR></H4><P> +PostgreSQL does not support outer joins in the current release. They can +be simulated using <small>UNION</small> and <small>NOT IN</small>. For +example, when joining <i>tab1</i> and <i>tab2,</i> the following query +does an <i>outer</i> join of the two tables: +<PRE> + SELECT tab1.col1, tab2.col2 + FROM tab1, tab2 + WHERE tab1.col1 = tab2.col1 + UNION ALL + SELECT tab1.col1, NULL + FROM tab1 + WHERE tab1.col1 NOT IN (SELECT tab2.col1 FROM tab2) + ORDER BY tab1.col1 +</PRE> + <HR> <H2><CENTER>Extending PostgreSQL</CENTER></H2><P> -<H4><A NAME="5.1">5.1</A>) I wrote a user-defined function. When +<H4><A NAME="5.1">5.1</A>) I wrote a user-defined function. When I run it in <I>psql,</I> why does it dump core?</H4><P> The problem could be a number of things. Try testing your user-defined -function in a stand alone test program first. +function in a stand-alone test program first. -<H4><A NAME="5.2">5.2</A>) What does the message: -<I>NOTICE:PortalHeapMemoryFree: 0x402251d0 not in alloc set!</I> mean?</H4><P> +<H4><A NAME="5.2">5.2</A>) What does the message +<I>"NOTICE:PortalHeapMemoryFree: 0x402251d0 not in alloc set!"</I> mean?</H4><P> -You are <I>pfree'ing</I> something that was not <I>palloc'ed.</I> +You are <I>pfree'</I>ing something that was not <I>palloc'</I>ed. Beware of mixing <I>malloc/free</I> and <I>palloc/pfree.</I> -<H4><A NAME="5.3">5.3</A>) How can I contribute some nifty new types and -functions for PostgreSQL?</H4><P> +<H4><A NAME="5.3">5.3</A>) How can I contribute some nifty new types and +functions to PostgreSQL?</H4><P> -Send your extensions to the pgsql-hackers mailing list, and they will +Send your extensions to the <I>pgsql-hackers</I> mailing list, and they will eventually end up in the <I>contrib/</I> subdirectory.<P> -<H4><A NAME="5.4">5.4</A>) How do I write a C function to return a +<H4><A NAME="5.4">5.4</A>) How do I write a C function to return a tuple?</H4><P> This requires wizardry so extreme that the authors have never tried it, though in principle it can be done.<P> -<H4><A NAME="5.5">5.5</A>) I have changed a source file. Why does the -recompile does not see the change?</H4><P> +<H4><A NAME="5.5">5.5</A>) I have changed a source file. Why does the +recompile not see the change?</H4><P> -The Makefiles do not have the proper dependencies for include files. You -have to do a <I>make clean</I> and then another <I>make</I>. - You -have to do a <I>make clean</I> and then another <I>make.</I><P> +The <I>Makefiles</I> do not have the proper dependencies for include files. You +have to do a <I>make clean</I> and then another <I>make</I>.<P> </BODY> </HTML> - |