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>