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Add a function pg_stat_clear_snapshot() that discards any statistics snapshot

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already collected in the current transaction; this allows plpgsql functions to
watch for stats updates even though they are confined to a single transaction.
Use this instead of the previous kluge involving pg_stat_file() to wait for
the stats collector to update in the stats regression test.  Internally,
decouple storage of stats snapshots from transaction boundaries; they'll
now stick around until someone calls pgstat_clear_snapshot --- which xact.c
still does at transaction end, to maintain the previous behavior.  This makes
the logic a lot cleaner, at the price of a couple dozen cycles per transaction
exit.
This commit is contained in:
Tom Lane
2007-02-07 23:11:30 +00:00
parent d9ce68872f
commit aec4cf1c8c
9 changed files with 192 additions and 170 deletions
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22
doc/src/sgml/monitoring.sgml
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@ -1,4 +1,4 @@
<!-- $PostgreSQL: pgsql/doc/src/sgml/monitoring.sgml,v 1.45 2007/02/01 00:28:17 momjian Exp $ -->
<!-- $PostgreSQL: pgsql/doc/src/sgml/monitoring.sgml,v 1.46 2007/02/07 23:11:29 tgl Exp $ -->
<chapter id="monitoring">
<title>Monitoring Database Activity</title>
@ -227,7 +227,10 @@ postgres: <replaceable>user</> <replaceable>database</> <replaceable>host</> <re
queries on the statistics and correlate the results without worrying that
the numbers are changing underneath you. But if you want to see new
results with each query, be sure to do the queries outside any transaction
block.
block. Alternatively, you can invoke
<function>pg_stat_clear_snapshot</function>(), which will discard the
current transaction's statistics snapshot (if any). The next use of
statistical information will cause a new snapshot to be fetched.
</para>
<table id="monitoring-stats-views-table">
@ -708,10 +711,19 @@ postgres: <replaceable>user</> <replaceable>database</> <replaceable>host</> <re
</row>
<row>
<entry><literal><function>pg_stat_reset</function>()</literal></entry>
<entry><type>boolean</type></entry>
<entry><literal><function>pg_stat_clear_snapshot</function>()</literal></entry>
<entry><type>void</type></entry>
<entry>
Reset all block-level and row-level statistics to zero
Discard the current statistics snapshot
</entry>
</row>
<row>
<entry><literal><function>pg_stat_reset</function>()</literal></entry>
<entry><type>void</type></entry>
<entry>
Reset all statistics counters for the current database to zero
(requires superuser privileges)
</entry>
</row>
</tbody>