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pgstat: store statistics in shared memory.

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Previously the statistics collector received statistics updates via UDP and
shared statistics data by writing them out to temporary files regularly. These
files can reach tens of megabytes and are written out up to twice a
second. This has repeatedly prevented us from adding additional useful
statistics.

Now statistics are stored in shared memory. Statistics for variable-numbered
objects are stored in a dshash hashtable (backed by dynamic shared
memory). Fixed-numbered stats are stored in plain shared memory.

The header for pgstat.c contains an overview of the architecture.

The stats collector is not needed anymore, remove it.

By utilizing the transactional statistics drop infrastructure introduced in a
prior commit statistics entries cannot "leak" anymore. Previously leaked
statistics were dropped by pgstat_vacuum_stat(), called from [auto-]vacuum. On
systems with many small relations pgstat_vacuum_stat() could be quite
expensive.

Now that replicas drop statistics entries for dropped objects, it is not
necessary anymore to reset stats when starting from a cleanly shut down
replica.

Subsequent commits will perform some further code cleanup, adapt docs and add
tests.

Bumps PGSTAT_FILE_FORMAT_ID.

Author: Kyotaro Horiguchi <horikyota.ntt@gmail.com>
Author: Andres Freund <andres@anarazel.de>
Author: Melanie Plageman <melanieplageman@gmail.com>
Reviewed-By: Andres Freund <andres@anarazel.de>
Reviewed-By: Thomas Munro <thomas.munro@gmail.com>
Reviewed-By: Justin Pryzby <pryzby@telsasoft.com>
Reviewed-By: "David G. Johnston" <david.g.johnston@gmail.com>
Reviewed-By: Tomas Vondra <tomas.vondra@2ndquadrant.com> (in a much earlier version)
Reviewed-By: Arthur Zakirov <a.zakirov@postgrespro.ru> (in a much earlier version)
Reviewed-By: Antonin Houska <ah@cybertec.at> (in a much earlier version)
Discussion: https://postgr.es/m/20220303021600.hs34ghqcw6zcokdh@alap3.anarazel.de
Discussion: https://postgr.es/m/20220308205351.2xcn6k4x5yivcxyd@alap3.anarazel.de
Discussion: https://postgr.es/m/20210319235115.y3wz7hpnnrshdyv6@alap3.anarazel.de
This commit is contained in:
Andres Freund
2022-04-06 21:29:46 -07:00
parent be902e2651
commit 5891c7a8ed
50 changed files with 4395 additions and 5485 deletions
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19
doc/src/sgml/monitoring.sgml
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@ -1110,10 +1110,6 @@ postgres 27093 0.0 0.0 30096 2752 ? Ss 11:34 0:00 postgres: ser
<entry><literal>LogicalLauncherMain</literal></entry>
<entry>Waiting in main loop of logical replication launcher process.</entry>
</row>
<row>
<entry><literal>PgStatMain</literal></entry>
<entry>Waiting in main loop of statistics collector process.</entry>
</row>
<row>
<entry><literal>RecoveryWalStream</literal></entry>
<entry>Waiting in main loop of startup process for WAL to arrive, during
@ -2115,6 +2111,18 @@ postgres 27093 0.0 0.0 30096 2752 ? Ss 11:34 0:00 postgres: ser
<entry>Waiting to access the list of predicate locks held by
serializable transactions.</entry>
</row>
<row>
<entry><literal>PgStatsDSA</literal></entry>
<entry>Waiting for stats dynamic shared memory allocator access</entry>
</row>
<row>
<entry><literal>PgStatsHash</literal></entry>
<entry>Waiting for stats shared memory hash table access</entry>
</row>
<row>
<entry><literal>PgStatsData</literal></entry>
<entry>Waiting for shared memory stats data access</entry>
</row>
<row>
<entry><literal>SerializableXactHash</literal></entry>
<entry>Waiting to read or update information about serializable
@ -5142,7 +5150,8 @@ SELECT pid, wait_event_type, wait_event FROM pg_stat_activity WHERE wait_event i
<returnvalue>timestamp with time zone</returnvalue>
</para>
<para>
Returns the timestamp of the current statistics snapshot.
Returns the timestamp of the current statistics snapshot, or NULL if
no statistics snapshot has been taken.
</para></entry>
</row>