Hello, when maintenance_work_mem and autovacuum_work_mem are set, my
understanding is that the vacuum and autovacuum sessions should be limited
to use the memory limits set by these parameters. But I am seeing more
memory being used than these limits by autovacuum sessions, any reason why
this would happen?

Please see below examples, where maintenance_work_mem is set to 20mb and
shared_buffers is 128mb. When I see the memory for this session in top, it
shows 162mb. But when default_statistics_target is increased to 3000, the
session usage is 463mb, which is way more than 20mb maintenance_work_mem
and 128mb shared_buffer. Shouldn't the process memory be capped to 20+128mb?

postgres=# show maintenance_work_mem ;
 maintenance_work_mem ----------------------
 20MB
(1 row)
postgres=# vacuum analyze mdm_context;
VACUUM
postgres=# show shared_buffers;
 shared_buffers ----------------
 128MB
(1 row)

   PID USER      PR  NI    VIRT    RES    SHR S %CPU %MEM     TIME+
COMMAND
 62246 postgres  20   0  422892 165996 139068 R 57.1 15.7  25:06.34
postgres: postgres postgres [local] VACUUM


postgres=# show default_statistics_target;
 default_statistics_target ---------------------------
 100
(1 row)
postgres=# set default_statistics_target=3000;SET
postgres=# vacuum analyze mdm_context;
VACUUM

    PID USER      PR  NI    VIRT    RES    SHR S %CPU %MEM     TIME+
COMMAND
 62246 postgres  20   0  876132 474384   2976 R 62.9 47.6  25:11.41
postgres: postgres postgres [local] VACUUM

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