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diff --git a/contrib/likeplanning/README b/contrib/likeplanning/README deleted file mode 100644 index 0896966376..0000000000 --- a/contrib/likeplanning/README +++ /dev/null @@ -1,44 +0,0 @@ -This directory contains two SQL scripts that control use of some new -code for planning/optimizing queries containing LIKE and -regular-expression operators. This code was added to Postgres 7.0 late in -beta test, and it hasn't gotten enough testing to warrant turning it on by -default in release 7.0 (although it probably will become default in 7.1). -So, here are some scripts to enable and disable it. You may want to run -these scripts if you have problems with the planner choosing bad plans for -queries involving LIKE or regexps in WHERE clauses. - - -HOW TO USE THE SCRIPTS ----------------------- - -Both scripts must be run as the Postgres superuser. The easiest -way to run an SQL script is - psql -f scriptfile databasename -or you can start psql interactively and enter - \i scriptfile - -enablelike.sql enables use of the new planning code in the database in -which it is run. If you run it in template1, all subsequently-created -databases will use the new code by default. - -disablelike.sql reverts to the old planning code for LIKE, in the database -in which it is run. If you run it in template1, all subsequently-created -databases will use the old code by default. - - -WHAT IT DOES ------------- - -These scripts install (or disable) new code for "selectivity estimation" -of LIKE and regexp operators. Selectivity estimation determines the -estimated number of rows produced by a query or subquery, and that in turn -determines the kind of plan the planner will use. The old selectivity -estimator ignored the pattern being searched for and just produced the -same estimate as for an "=" operator, which of course was usually too low -for a wildcard match. The new code has some knowledge of pattern matching -rules and generates an estimate based on the number of fixed characters and -wildcards present in the pattern. Also, if the pattern has a fixed prefix -that must be matched (such as LIKE 'foo%' or ~ '^foo'), an appropriate -range-query selectivity estimate is produced and factored into the result. - -If you want to look at the code itself, see src/backend/utils/adt/selfuncs.c. |