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Revert function to get memory context stats for processes

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Due to concerns raised about the approach, and memory leaks found
in sensitive contexts the functionality is reverted. This reverts
commits 45e7e8ca9, f8c115a6c, d2a1ed172, 55ef7abf8 and 042a66291
for v18 with an intent to revisit this patch for v19.

Discussion: https://postgr.es/m/594293.1747708165@sss.pgh.pa.us
This commit is contained in:
Daniel Gustafsson
2025-05-23 15:44:54 +02:00
parent 70a13c528b
commit fb844b9f06
29 changed files with 47 additions and 1400 deletions
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171
doc/src/sgml/func.sgml
View File

@ -28663,143 +28663,6 @@ acl | {postgres=arwdDxtm/postgres,foo=r/postgres}
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>pg_get_process_memory_contexts</primary>
</indexterm>
<function>pg_get_process_memory_contexts</function> ( <parameter>pid</parameter> <type>integer</type>, <parameter>summary</parameter> <type>boolean</type>, <parameter>timeout</parameter> <type>float</type> )
<returnvalue>setof record</returnvalue>
( <parameter>name</parameter> <type>text</type>,
<parameter>ident</parameter> <type>text</type>,
<parameter>type</parameter> <type>text</type>,
<parameter>path</parameter> <type>integer[]</type>,
<parameter>level</parameter> <type>integer</type>,
<parameter>total_bytes</parameter> <type>bigint</type>,
<parameter>total_nblocks</parameter> <type>bigint</type>,
<parameter>free_bytes</parameter> <type>bigint</type>,
<parameter>free_chunks</parameter> <type>bigint</type>,
<parameter>used_bytes</parameter> <type>bigint</type>,
<parameter>num_agg_contexts</parameter> <type>integer</type>,
<parameter>stats_timestamp</parameter> <type>timestamptz</type> )
</para>
<para>
This function handles requests to display the memory contexts of a
<productname>PostgreSQL</productname> process with the specified
process ID. The function can be used to send requests to backends as
well as <glossterm linkend="glossary-auxiliary-proc">auxiliary processes</glossterm>.
</para>
<para>
The returned record contains extended statistics per each memory
context:
<itemizedlist spacing="compact">
<listitem>
<para>
<parameter>name</parameter> - The name of the memory context.
</para>
</listitem>
<listitem>
<para>
<parameter>ident</parameter> - Memory context ID (if any).
</para>
</listitem>
<listitem>
<para>
<parameter>type</parameter> - The type of memory context, possible
values are: AllocSet, Generation, Slab and Bump.
</para>
</listitem>
<listitem>
<para>
<parameter>path</parameter> - Memory contexts are organized in a
tree model with TopMemoryContext as the root, and all other memory
contexts as nodes in the tree. The <parameter>path</parameter>
displays the path from the root to the current memory context. The
path is limited to 100 children per node, which each node limited
to a max depth of 100, to preserve memory during reporting. The
printed path will also be limited to 100 nodes counting from the
TopMemoryContext.
</para>
</listitem>
<listitem>
<para>
<parameter>level</parameter> - The level in the tree of the current
memory context.
</para>
</listitem>
<listitem>
<para>
<parameter>total_bytes</parameter> - The total number of bytes
allocated to this memory context.
</para>
</listitem>
<listitem>
<para>
<parameter>total_nblocks</parameter> - The total number of blocks
used for the allocated memory.
</para>
</listitem>
<listitem>
<para>
<parameter>free_bytes</parameter> - The amount of free memory in
this memory context.
</para>
</listitem>
<listitem>
<para>
<parameter>free_chunks</parameter> - The number of chunks that
<parameter>free_bytes</parameter> corresponds to.
</para>
</listitem>
<listitem>
<para>
<parameter>used_bytes</parameter> - The total number of bytes
currently occupied.
</para>
</listitem>
<listitem>
<para>
<parameter>num_agg_contexts</parameter> - The number of memory
contexts aggregated in the displayed statistics.
</para>
</listitem>
<listitem>
<para>
<parameter>stats_timestamp</parameter> - When the statistics were
extracted from the process.
</para>
</listitem>
</itemizedlist>
</para>
<para>
When <parameter>summary</parameter> is <literal>true</literal>, statistics
for memory contexts at levels 1 and 2 are displayed, with level 1
representing the root node (i.e., <literal>TopMemoryContext</literal>).
Statistics for contexts on level 2 and below are aggregates of all
child contexts' statistics, where <literal>num_agg_contexts</literal>
indicate the number aggregated child contexts. When
<parameter>summary</parameter> is <literal>false</literal>,
<literal>the num_agg_contexts</literal> value is <literal>1</literal>,
indicating that individual statistics are being displayed.
</para>
<para>
Busy processes can delay reporting memory context statistics,
<parameter>timeout</parameter> specifies the number of seconds
to wait for updated statistics. <parameter>timeout</parameter> can be
specified in fractions of a second.
</para>
<para>
After receiving memory context statistics from the target process, it
returns the results as one row per context. If all the contexts don't
fit within the pre-determined size limit, the remaining context
statistics are aggregated and a cumulative total is displayed. The
<literal>num_agg_contexts</literal> column indicates the number of
contexts aggregated in the displayed statistics. When
<literal>num_agg_contexts</literal> is <literal>1</literal> it means
that the context statistics are displayed separately.
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
@ -28939,40 +28802,6 @@ LOG: Grand total: 1651920 bytes in 201 blocks; 622360 free (88 chunks); 1029560
because it may generate a large number of log messages.
</para>
<para>
<function>pg_get_process_memory_contexts</function> can be used to request
memory contexts statistics of any <productname>PostgreSQL</productname>
process. For example:
<programlisting>
postgres=# SELECT * FROM pg_get_process_memory_contexts(
(SELECT pid FROM pg_stat_activity
WHERE backend_type = 'checkpointer'),
false, 0.5) LIMIT 1;
-[ RECORD 1 ]----+------------------------------
name | TopMemoryContext
ident |
type | AllocSet
path | {1}
level | 1
total_bytes | 90304
total_nblocks | 3
free_bytes | 2880
free_chunks | 1
used_bytes | 87424
num_agg_contexts | 1
stats_timestamp | 2025-03-24 13:55:47.796698+01
</programlisting>
<note>
<para>
While <function>pg_get_process_memory_contexts</function> can be used to
query memory contexts of the local backend,
<structname>pg_backend_memory_contexts</structname>
(see <xref linkend="view-pg-backend-memory-contexts"/> for more details)
will be less resource intensive when only the local backend is of interest.
</para>
</note>
</para>
</sect2>
<sect2 id="functions-admin-backup">

15
doc/src/sgml/release-18.sgml
View File

@ -961,21 +961,6 @@ This is true even if the tables in different schemas have different column names
</para>
</listitem>
<!--
Author: Daniel Gustafsson <dgustafsson@postgresql.org>
2025-04-08 [042a66291] Add function to get memory context stats for processes
Author: Daniel Gustafsson <dgustafsson@postgresql.org>
2025-04-08 [c57971034] Rename argument in pg_get_process_memory_contexts().
-->
<listitem>
<para>
Add function pg_get_process_memory_contexts() to report process memory context statistics (Rahila Syed)
<ulink url="&commit_baseurl;042a66291">&sect;</ulink>
<ulink url="&commit_baseurl;c57971034">&sect;</ulink>
</para>
</listitem>
<!--
Author: David Rowley <drowley@postgresql.org>
2024-07-01 [12227a1d5] Add context type field to pg_backend_memory_contexts