Re: Add the ability to limit the amount of memory that can be allocated to backends.

hi.

+static void checkAllocations();
should be "static void checkAllocations(void);" ?

PgStatShared_Memtrack there is a lock, but seems not initialized, and
not used. Can you expand on it?
So in view  pg_stat_global_memory_tracking, column
"total_memory_reserved" is a point of time, total memory the whole
server reserved/malloced? will it change every time you call it?
the function pg_stat_get_global_memory_tracking provolatile => 's'.
should be a VOLATILE function?


pg_stat_get_memory_reservation, pg_stat_get_global_memory_tracking
should be proretset => 'f'.
+{ oid => '9891',
+  descr => 'statistics: memory utilized by current backend',
+  proname => 'pg_get_backend_memory_allocation', prorows => '1',
proisstrict => 'f',
+  proretset => 't', provolatile => 's', proparallel => 'r',


you declared
+void pgstat_backend_memory_reservation_cb(void);
but seems there is no definition.


this part is unnecessary since you already declared
src/include/catalog/pg_proc.dat?
+/* SQL Callable functions */
+extern Datum pg_stat_get_memory_reservation(PG_FUNCTION_ARGS);
+extern Datum pg_get_backend_memory_allocation(PG_FUNCTION_ARGS);
+extern Datum pg_stat_get_global_memory_tracking(PG_FUNCTION_ARGS);

The last sentence is just a plain link, no explanation. something is missing?
     <para>
+      Reports how much memory remains available to the server. If a
+      backend process attempts to allocate more memory than remains,
+      the process will fail with an out of memory error, resulting in
+      cancellation of the process's active query/transaction.
+      If memory is not being limited (ie. max_total_memory is zero or not set),
+      this column returns NULL.
+      <xref linkend="guc-max-total-memory"/>.
+     </para></entry>
+     </row>
+
+      <row>
+       <entry role="catalog_table_entry"><para role="column_definition">
+        <structfield>static_shared_memory</structfield> <type>bigint</type>
+       </para>
+      <para>
+       Reports how much static shared memory (non-DSM shared memory)
is being used by
+       the server. Static shared memory is configured by the postmaster at
+       at server startup.
+       <xref linkend="guc-max-total-memory"/>.
+      </para></entry>
+      </row>