Rework design of functions in pg_walinspect

This commit reworks a bit the set-returning functions of pg_walinspect,
making them more flexible regarding their end LSN:
- pg_get_wal_records_info()
- pg_get_wal_stats()
- pg_get_wal_block_info()

The end LSNs given to these functions is now handled so as a value
higher than the current LSN of the cluster (insert LSN for a primary, or
replay LSN for a standby) does not raise an error, giving more
flexibility to monitoring queries.  Instead, the functions return
results up to the current LSN, as found at the beginning of each
function call.

As an effect of that, pg_get_wal_records_info_till_end_of_wal() and
pg_get_wal_stats_till_end_of_wal() are now removed from 1.1, as the
existing, equivalent functions are able to offer the same
possibilities.

Author: Bharath Rupireddy
Discussion: https://postgr.es/m/CALj2ACU0_q-o4DSweyaW9NO1KBx-QkN6G_OzYQvpjf3CZVASkg@mail.gmail.com

1 files changed, 15 insertions, 44 deletions

diff --git a/doc/src/sgml/pgwalinspect.sgml b/doc/src/sgml/pgwalinspect.sgml
index 3b19863dce..9a0241a8d6 100644
--- a/doc/src/sgml/pgwalinspect.sgml
+++ b/doc/src/sgml/pgwalinspect.sgml
@@ -94,9 +94,11 @@ block_ref        | blkref #0: rel 1663/5/60221 fork main blk 2
      <para>
       Gets information of all the valid WAL records between
       <replaceable>start_lsn</replaceable> and <replaceable>end_lsn</replaceable>.
-      Returns one row per WAL record. If <replaceable>start_lsn</replaceable>
-      or <replaceable>end_lsn</replaceable> are not yet available, the
-      function will raise an error. For example:
+      Returns one row per WAL record. If a future
+      <replaceable>end_lsn</replaceable> (i.e. ahead of the current LSN of
+      the server) is specified, it returns information until the end of WAL.
+      The function raises an error if <replaceable>start_lsn</replaceable>
+      is not available. For example, usage of the function is as follows:
 <screen>
 postgres=# SELECT * FROM pg_get_wal_records_info('0/1E913618', '0/1E913740') LIMIT 1;
 -[ RECORD 1 ]----+--------------------------------------------------------------
@@ -116,23 +118,6 @@ block_ref        |
     </listitem>
    </varlistentry>
 
-    <varlistentry id="pgwalinspect-funcs-pg-get-wal-records-info-till-end-of-wal">
-    <term>
-     <function>
-      pg_get_wal_records_info_till_end_of_wal(start_lsn pg_lsn)
-      returns setof record
-     </function>
-    </term>
-
-    <listitem>
-     <para>
-      This function is the same as <function>pg_get_wal_records_info()</function>,
-      except that it gets information of all the valid WAL records from
-      <replaceable>start_lsn</replaceable> till the end of WAL.
-     </para>
-    </listitem>
-   </varlistentry>
-
     <varlistentry id="pgwalinspect-funcs-pg-get-wal-stats">
     <term>
      <function>
@@ -148,10 +133,11 @@ block_ref        |
       <replaceable>end_lsn</replaceable>. By default, it returns one row per
       <replaceable>resource_manager</replaceable> type. When
       <replaceable>per_record</replaceable> is set to <literal>true</literal>,
-      it returns one row per <replaceable>record_type</replaceable>.
-      If <replaceable>start_lsn</replaceable>
-      or <replaceable>end_lsn</replaceable> are not yet available, the
-      function will raise an error. For example:
+      it returns one row per <replaceable>record_type</replaceable>. If a
+      future <replaceable>end_lsn</replaceable> (i.e. ahead of the current
+      LSN of the server) is specified, it returns statistics until the end
+      of WAL. An error is raised if <replaceable>start_lsn</replaceable> is
+      not available. For example, usage of the function is as follows:
 <screen>
 postgres=# SELECT * FROM pg_get_wal_stats('0/1E847D00', '0/1E84F500')
              WHERE count > 0 LIMIT 1 AND
@@ -171,23 +157,6 @@ combined_size_percentage     | 2.8634072910530795
     </listitem>
    </varlistentry>
 
-    <varlistentry id="pgwalinspect-funcs-pg-get-wal-stats-till-end-of-wal">
-    <term>
-     <function>
-      pg_get_wal_stats_till_end_of_wal(start_lsn pg_lsn, per_record boolean DEFAULT false)
-      returns setof record
-     </function>
-    </term>
-
-    <listitem>
-     <para>
-      This function is the same as <function>pg_get_wal_stats()</function>,
-      except that it gets statistics of all the valid WAL records from
-      <replaceable>start_lsn</replaceable> till end of WAL.
-     </para>
-    </listitem>
-   </varlistentry>
-
    <varlistentry>
     <term>
      <function>pg_get_wal_block_info(start_lsn pg_lsn, end_lsn pg_lsn) returns setof record</function>
@@ -202,9 +171,11 @@ combined_size_percentage     | 2.8634072910530795
       and their information associated with all the valid WAL records between
       <replaceable>start_lsn</replaceable> and
       <replaceable>end_lsn</replaceable>. Returns one row per block registered
-      in a WAL record. If <replaceable>start_lsn</replaceable> or
-      <replaceable>end_lsn</replaceable> are not yet available, the function
-      will raise an error. For example:
+      in a WAL record. If a future <replaceable>end_lsn</replaceable> (i.e.
+      ahead of the current LSN of the server) is specified, it returns
+      statistics until the end of WAL. An error is raised if
+      <replaceable>start_lsn</replaceable> is not available. For example,
+      usage of the function is as follows:
 <screen>
 postgres=# SELECT lsn, blockid, reltablespace, reldatabase, relfilenode,
                   relblocknumber, forkname,