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Rename SLRU structures and associated LWLocks.
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Originally, the names assigned to SLRUs had no purpose other than
being shmem lookup keys, so not a lot of thought went into them.
As of v13, though, we're exposing them in the pg_stat_slru view and
the pg_stat_reset_slru function, so it seems advisable to take a bit
more care.  Rename them to names based on the associated on-disk
storage directories (which fortunately we *did* think about, to some
extent; since those are also visible to DBAs, consistency seems like
a good thing).  Also rename the associated LWLocks, since those names
are likewise user-exposed now as wait event names.

For the most part I only touched symbols used in the respective modules'
SimpleLruInit() calls, not the names of other related objects.  This
renaming could have been taken further, and maybe someday we will do so.
But for now it seems undesirable to change the names of any globally
visible functions or structs, so some inconsistency is unavoidable.

(But I *did* terminate "oldserxid" with prejudice, as I found that
name both unreadable and not descriptive of the SLRU's contents.)

Table 27.12 needs re-alphabetization now, but I'll leave that till
after the other LWLock renamings I have in mind.

Discussion: https://postgr.es/m/[email protected]
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tglsfdc committed May 15, 2020
1 parent 756abe2 commit 5da1493
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89 changes: 51 additions & 38 deletions doc/src/sgml/monitoring.sgml
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Original file line number Diff line number Diff line change
Expand Up @@ -1754,12 +1754,13 @@ postgres 27093 0.0 0.0 30096 2752 ? Ss 11:34 0:00 postgres: ser
<entry>Waiting to manage space allocation in shared memory.</entry>
</row>
<row>
<entry><literal>AsyncCtlLock</literal></entry>
<entry>Waiting to read or update shared notification state.</entry>
<entry><literal>NotifySLRULock</literal></entry>
<entry>Waiting to access the <command>NOTIFY</command> message SLRU
cache.</entry>
</row>
<row>
<entry><literal>AsyncQueueLock</literal></entry>
<entry>Waiting to read or update notification messages.</entry>
<entry><literal>NotifyQueueLock</literal></entry>
<entry>Waiting to read or update <command>NOTIFY</command> messages.</entry>
</row>
<row>
<entry><literal>AutoFileLock</literal></entry>
Expand All @@ -1785,13 +1786,13 @@ postgres 27093 0.0 0.0 30096 2752 ? Ss 11:34 0:00 postgres: ser
B-tree index.</entry>
</row>
<row>
<entry><literal>CLogControlLock</literal></entry>
<entry>Waiting to read or update transaction status.</entry>
<entry><literal>XactSLRULock</literal></entry>
<entry>Waiting to access the transaction status SLRU cache.</entry>
</row>
<row>
<entry><literal>CLogTruncationLock</literal></entry>
<entry><literal>XactTruncationLock</literal></entry>
<entry>Waiting to execute <function>pg_xact_status</function> or update
the oldest transaction id available to it.</entry>
the oldest transaction ID available to it.</entry>
</row>
<row>
<entry><literal>CheckpointLock</literal></entry>
Expand All @@ -1802,8 +1803,8 @@ postgres 27093 0.0 0.0 30096 2752 ? Ss 11:34 0:00 postgres: ser
<entry>Waiting to manage fsync requests.</entry>
</row>
<row>
<entry><literal>CommitTsControlLock</literal></entry>
<entry>Waiting to read or update transaction commit timestamps.</entry>
<entry><literal>CommitTsSLRULock</literal></entry>
<entry>Waiting to access the commit timestamp SLRU cache.</entry>
</row>
<row>
<entry><literal>CommitTsLock</literal></entry>
Expand All @@ -1828,12 +1829,12 @@ postgres 27093 0.0 0.0 30096 2752 ? Ss 11:34 0:00 postgres: ser
<entry>Waiting to read or update shared multixact state.</entry>
</row>
<row>
<entry><literal>MultiXactMemberControlLock</literal></entry>
<entry>Waiting to read or update multixact member mappings.</entry>
<entry><literal>MultiXactMemberSLRULock</literal></entry>
<entry>Waiting to access the multixact member SLRU cache.</entry>
</row>
<row>
<entry><literal>MultiXactOffsetControlLock</literal></entry>
<entry>Waiting to read or update multixact offset mappings.</entry>
<entry><literal>MultiXactOffsetSLRULock</literal></entry>
<entry>Waiting to access the multixact offset SLRU cache.</entry>
</row>
<row>
<entry><literal>MultiXactTruncationLock</literal></entry>
Expand All @@ -1844,9 +1845,9 @@ postgres 27093 0.0 0.0 30096 2752 ? Ss 11:34 0:00 postgres: ser
<entry>Waiting to allocate or assign an OID.</entry>
</row>
<row>
<entry><literal>OldSerXidLock</literal></entry>
<entry>Waiting to read or record conflicting serializable
transactions.</entry>
<entry><literal>SerialSLRULock</literal></entry>
<entry>Waiting to access the serializable transaction conflict SLRU
cache.</entry>
</row>
<row>
<entry><literal>OldSnapshotTimeMapLock</literal></entry>
Expand Down Expand Up @@ -1907,8 +1908,8 @@ postgres 27093 0.0 0.0 30096 2752 ? Ss 11:34 0:00 postgres: ser
<entry>Waiting to find or allocate space in shared memory.</entry>
</row>
<row>
<entry><literal>SubtransControlLock</literal></entry>
<entry>Waiting to read or update sub-transaction information.</entry>
<entry><literal>SubtransSLRULock</literal></entry>
<entry>Waiting to access the sub-transaction SLRU cache.</entry>
</row>
<row>
<entry><literal>SyncRepLock</literal></entry>
Expand Down Expand Up @@ -1941,8 +1942,9 @@ postgres 27093 0.0 0.0 30096 2752 ? Ss 11:34 0:00 postgres: ser
<entry>Waiting to allocate or assign a transaction id.</entry>
</row>
<row>
<entry><literal>async</literal></entry>
<entry>Waiting for I/O on an async (notify) buffer.</entry>
<entry><literal>NotifyBuffer</literal></entry>
<entry>Waiting for I/O on a <command>NOTIFY</command> message SLRU
buffer.</entry>
</row>
<row>
<entry><literal>buffer_content</literal></entry>
Expand All @@ -1958,29 +1960,30 @@ postgres 27093 0.0 0.0 30096 2752 ? Ss 11:34 0:00 postgres: ser
pool.</entry>
</row>
<row>
<entry><literal>clog</literal></entry>
<entry>Waiting for I/O on a clog (transaction status) buffer.</entry>
<entry><literal>XactBuffer</literal></entry>
<entry>Waiting for I/O on a transaction status SLRU buffer.</entry>
</row>
<row>
<entry><literal>commit_timestamp</literal></entry>
<entry>Waiting for I/O on commit timestamp buffer.</entry>
<entry><literal>CommitTsBuffer</literal></entry>
<entry>Waiting for I/O on a commit timestamp SLRU buffer.</entry>
</row>
<row>
<entry><literal>lock_manager</literal></entry>
<entry>Waiting to add or examine locks for backends, or waiting to
join or exit a locking group (used by parallel query).</entry>
</row>
<row>
<entry><literal>multixact_member</literal></entry>
<entry>Waiting for I/O on a multixact_member buffer.</entry>
<entry><literal>MultiXactMember</literal></entry>
<entry>Waiting for I/O on a multixact member SLRU buffer.</entry>
</row>
<row>
<entry><literal>multixact_offset</literal></entry>
<entry>Waiting for I/O on a multixact offset buffer.</entry>
<entry><literal>MultiXactOffsetBuffer</literal></entry>
<entry>Waiting for I/O on a multixact offset SLRU buffer.</entry>
</row>
<row>
<entry><literal>oldserxid</literal></entry>
<entry>Waiting for I/O on an oldserxid buffer.</entry>
<entry><literal>SerialBuffer</literal></entry>
<entry>Waiting for I/O on a serializable transaction conflict SLRU
buffer.</entry>
</row>
<row>
<entry><literal>parallel_append</literal></entry>
Expand Down Expand Up @@ -2018,8 +2021,8 @@ postgres 27093 0.0 0.0 30096 2752 ? Ss 11:34 0:00 postgres: ser
in a parallel query.</entry>
</row>
<row>
<entry><literal>subtrans</literal></entry>
<entry>Waiting for I/O on a subtransaction buffer.</entry>
<entry><literal>SubtransBuffer</literal></entry>
<entry>Waiting for I/O on a sub-transaction SLRU buffer.</entry>
</row>
<row>
<entry><literal>tbm</literal></entry>
Expand Down Expand Up @@ -4190,7 +4193,13 @@ SELECT pid, wait_event_type, wait_event FROM pg_stat_activity WHERE wait_event i
</tgroup>
</table>

<indexterm>
<primary>SLRU</primary>
</indexterm>

<para>
<productname>PostgreSQL</productname> accesses certain on-disk information
via <firstterm>SLRU</firstterm> (simple least-recently-used) caches.
The <structname>pg_stat_slru</structname> view will contain
one row for each tracked SLRU cache, showing statistics about access
to cached pages.
Expand Down Expand Up @@ -4484,11 +4493,15 @@ SELECT pid, wait_event_type, wait_event FROM pg_stat_activity WHERE wait_event i
Resets statistics to zero for a single SLRU cache, or for all SLRUs in
the cluster. If the argument is NULL, all counters shown in
the <structname>pg_stat_slru</structname> view for all SLRU caches are
reset. The argument can be one of <literal>async</literal>,
<literal>clog</literal>, <literal>commit_timestamp</literal>,
<literal>multixact_offset</literal>,
<literal>multixact_member</literal>, <literal>oldserxid</literal>, or
<literal>subtrans</literal> to reset the counters for only that entry.
reset. The argument can be one of
<literal>CommitTs</literal>,
<literal>MultiXactMember</literal>,
<literal>MultiXactOffset</literal>,
<literal>Notify</literal>,
<literal>Serial</literal>,
<literal>Subtrans</literal>, or
<literal>Xact</literal>
to reset the counters for only that entry.
If the argument is <literal>other</literal> (or indeed, any
unrecognized name), then the counters for all other SLRU caches, such
as extension-defined caches, are reset.
Expand Down
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