Josh Berkus wrote: > > > You can see the current multixact value in pg_controldata output. Keep > > timestamped values of that somewhere (a table?) so that you can measure > > consumption rate. I don't think we provide SQL-level access to those > > values. > > Bleh. Do we provide SQL-level access in 9.4? If not, I think that's a > requirement before release. Telling users to monitor a setting using a > restricted-permission command-line utility which produces a > version-specific text file they have to parse is not going to win us a > lot of fans.
I found that I had written a very quick accessor function to multixact shared state data awhile ago. This might be useful for monitoring purposes. What do people think of including this for 9.5? It needs a small change to add the newly added oldestOffset (plus a little cleanup and docs). -- Álvaro Herrera http://www.2ndQuadrant.com/ PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services
>From 2134f7928cad8c8d1a1e2d752c9443fb44a92a7e Mon Sep 17 00:00:00 2001 From: Alvaro Herrera <alvhe...@alvh.no-ip.org> Date: Sun, 14 Jun 2015 11:48:58 -0300 Subject: [PATCH] pg_get_multixact_range --- src/backend/access/transam/multixact.c | 31 +++++++++++++++++++++++++++++++ src/include/catalog/pg_proc.h | 2 ++ 2 files changed, 33 insertions(+) diff --git a/src/backend/access/transam/multixact.c b/src/backend/access/transam/multixact.c index 516a89f..dedded3 100644 --- a/src/backend/access/transam/multixact.c +++ b/src/backend/access/transam/multixact.c @@ -3274,3 +3274,34 @@ pg_get_multixact_members(PG_FUNCTION_ARGS) SRF_RETURN_DONE(funccxt); } + +#include "access/htup_details.h" + +Datum +pg_get_multixact_range(PG_FUNCTION_ARGS); + +Datum +pg_get_multixact_range(PG_FUNCTION_ARGS) +{ + TupleDesc tupdesc; + HeapTuple htup; + Datum values[3]; + bool nulls[3]; + + /* Build a tuple descriptor for our result type */ + if (get_call_result_type(fcinfo, NULL, &tupdesc) != TYPEFUNC_COMPOSITE) + elog(ERROR, "return type must be a row type"); + tupdesc = BlessTupleDesc(tupdesc); + + LWLockAcquire(MultiXactGenLock, LW_SHARED); + values[0] = MultiXactState->oldestMultiXactId; + values[1] = MultiXactState->nextMXact; + values[2] = MultiXactState->nextOffset; + LWLockRelease(MultiXactGenLock); + + nulls[0] = nulls[1] = nulls[2] = false; + + htup = heap_form_tuple(tupdesc, values, nulls); + + PG_RETURN_DATUM(HeapTupleGetDatum(htup)); +} diff --git a/src/include/catalog/pg_proc.h b/src/include/catalog/pg_proc.h index 6b3d194..f87d3d0 100644 --- a/src/include/catalog/pg_proc.h +++ b/src/include/catalog/pg_proc.h @@ -3079,6 +3079,8 @@ DATA(insert OID = 1065 ( pg_prepared_xact PGNSP PGUID 12 1 1000 0 0 f f f f t t DESCR("view two-phase transactions"); DATA(insert OID = 3819 ( pg_get_multixact_members PGNSP PGUID 12 1 1000 0 0 f f f f t t v 1 0 2249 "28" "{28,28,25}" "{i,o,o}" "{multixid,xid,mode}" _null_ _null_ pg_get_multixact_members _null_ _null_ _null_ )); DESCR("view members of a multixactid"); +DATA(insert OID = 3401 ( pg_get_multixact_range PGNSP PGUID 12 1 0 0 0 f f f f t f s 0 0 2249 "" "{28,28,28}" "{o,o,o}" "{oldestmulti,nextmulti,nextoffset}" _null_ _null_ pg_get_multixact_range _null_ _null_ _null_ )); +DESCR("get range of live multixacts"); DATA(insert OID = 3581 ( pg_xact_commit_timestamp PGNSP PGUID 12 1 0 0 0 f f f f t f s 1 0 1184 "28" _null_ _null_ _null_ _null_ _null_ pg_xact_commit_timestamp _null_ _null_ _null_ )); DESCR("get commit timestamp of a transaction"); -- 2.1.4
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