From: Bruce Momjian <bruce@momjian.us>
To: Robert Haas <robertmhaas@gmail.com>
Cc: Josh Berkus <josh@agliodbs.com>
Cc: Alvaro Herrera <alvherre@2ndquadrant.com>
Cc: pgsql-hackers@postgresql.org <pgsql-hackers@postgresql.org>
Subject: Re: Need Multixact Freezing Docs
Date: Fri, 5 Sep 2014 19:39:36 -0400
Message-ID: <20140905233936.GA20146@momjian.us> (raw)
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On Wed, Sep 3, 2014 at 05:17:17PM -0400, Robert Haas wrote:
> > I had a look at this and came upon a problem --- there is no multi-xid
> > SQL data type, and in fact the system catalogs that store mxid values
> > use xid, e.g.:
> >
> > relminmxid | xid | not null
> >
> > With no mxid data type, there is no way to do function overloading to
> > cause age to call the mxid variant.
> >
> > Should we use an explicit mxid_age() function name? Add an mxid data
> > type?
>
> Maybe both. But mxid_age() is probably the simpler way forward just to start.
OK, patch applied using mxid_age() and no new data type.
--
Bruce Momjian <bruce@momjian.us> http://momjian.us
EnterpriseDB http://enterprisedb.com
+ Everyone has their own god. +
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http://www.postgresql.org/mailpref/pgsql-hackersAttachments:mxid-age.diff (text/x-diff, 4.3K) downloaddiff --git a/doc/src/sgml/maintenance.sgml b/doc/src/sgml/maintenance.sgmlnew file mode 100644index cf174f0..d692308
*** a/doc/src/sgml/maintenance.sgml
--- b/doc/src/sgml/maintenance.sgml
*************** HINT: Stop the postmaster and vacuum th
*** 640,646 ****
possible multixact ID still appearing in any tuple of that table.
If this value is older than
<xref linkend="guc-vacuum-multixact-freeze-table-age">, a whole-table
! scan is forced. Whole-table <command>VACUUM</> scans, regardless of
what causes them, enable advancing the value for that table.
Eventually, as all tables in all databases are scanned and their
oldest multixact values are advanced, on-disk storage for older
--- 640,651 ----
possible multixact ID still appearing in any tuple of that table.
If this value is older than
<xref linkend="guc-vacuum-multixact-freeze-table-age">, a whole-table
! scan is forced. <function>mxid_age()</> can be used on
! <structname>pg_class</>.<structfield>relminmxid</> to find its age.
! </para>
!
! <para>
! Whole-table <command>VACUUM</> scans, regardless of
what causes them, enable advancing the value for that table.
Eventually, as all tables in all databases are scanned and their
oldest multixact values are advanced, on-disk storage for older
diff --git a/src/backend/utils/adt/xid.c b/src/backend/utils/adt/xid.cnew file mode 100644index 602a9e5..ecb3cf5
*** a/src/backend/utils/adt/xid.c
--- b/src/backend/utils/adt/xid.c
***************
*** 16,21 ****
--- 16,22 ----
#include <limits.h>
+ #include "access/multixact.h"
#include "access/transam.h"
#include "access/xact.h"
#include "libpq/pqformat.h"
*************** xid_age(PG_FUNCTION_ARGS)
*** 100,105 ****
--- 101,121 ----
PG_RETURN_INT32(INT_MAX);
PG_RETURN_INT32((int32) (now - xid));
+ }+ + /*+ * mxid_age - compute age of a multi XID (relative to latest stable mxid)+ */+ Datum+ mxid_age(PG_FUNCTION_ARGS)+ {+ TransactionId xid = PG_GETARG_TRANSACTIONID(0);+ MultiXactId now = ReadNextMultiXactId();+ + if (!MultiXactIdIsValid(xid))+ PG_RETURN_INT32(INT_MAX);+ + PG_RETURN_INT32((int32) (now - xid));
}
/*
diff --git a/src/include/catalog/catversion.h b/src/include/catalog/catversion.hnew file mode 100644index e1b62a5..e0875b7
*** a/src/include/catalog/catversion.h
--- b/src/include/catalog/catversion.h
***************
*** 53,58 ****
*/
/* yyyymmddN */
! #define CATALOG_VERSION_NO 201408281
#endif
--- 53,58 ----
*/
/* yyyymmddN */
! #define CATALOG_VERSION_NO 201409021
#endif
diff --git a/src/include/catalog/pg_proc.h b/src/include/catalog/pg_proc.hnew file mode 100644index 5176ed0..09e138b
*** a/src/include/catalog/pg_proc.h
--- b/src/include/catalog/pg_proc.h
*************** DATA(insert OID = 1180 ( abstime PG
*** 1277,1282 ****
--- 1277,1284 ----
DESCR("convert timestamp with time zone to abstime");
DATA(insert OID = 1181 ( age PGNSP PGUID 12 1 0 0 0 f f f f t f s 1 0 23 "28" _null_ _null_ _null_ _null_ xid_age _null_ _null_ _null_ ));
DESCR("age of a transaction ID, in transactions before current transaction");
+ DATA(insert OID = 3218 ( mxid_age PGNSP PGUID 12 1 0 0 0 f f f f t f s 1 0 23 "28" _null_ _null_ _null_ _null_ mxid_age _null_ _null_ _null_ ));+ DESCR("age of a multi-transaction ID, in multi-transactions before current multi-transaction");
DATA(insert OID = 1188 ( timestamptz_mi PGNSP PGUID 12 1 0 0 0 f f f f t f i 2 0 1186 "1184 1184" _null_ _null_ _null_ _null_ timestamp_mi _null_ _null_ _null_ ));
DATA(insert OID = 1189 ( timestamptz_pl_interval PGNSP PGUID 12 1 0 0 0 f f f f t f s 2 0 1184 "1184 1186" _null_ _null_ _null_ _null_ timestamptz_pl_interval _null_ _null_ _null_ ));
diff --git a/src/include/utils/builtins.h b/src/include/utils/builtins.hnew file mode 100644index 78cc0a0..d88e7a3
*** a/src/include/utils/builtins.h
--- b/src/include/utils/builtins.h
*************** extern Datum xidrecv(PG_FUNCTION_ARGS);
*** 845,850 ****
--- 845,851 ----
extern Datum xidsend(PG_FUNCTION_ARGS);
extern Datum xideq(PG_FUNCTION_ARGS);
extern Datum xid_age(PG_FUNCTION_ARGS);
+ extern Datum mxid_age(PG_FUNCTION_ARGS);
extern int xidComparator(const void *arg1, const void *arg2);
extern Datum cidin(PG_FUNCTION_ARGS);
extern Datum cidout(PG_FUNCTION_ARGS);
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To: pgsql-hackers@postgresql.org
Cc: bruce@momjian.us, robertmhaas@gmail.com, josh@agliodbs.com, alvherre@2ndquadrant.com
Subject: Re: Need Multixact Freezing Docs
In-Reply-To: <20140905233936.GA20146@momjian.us>
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