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Implement mxid_age() to compute multi-xid age 

Report by Josh Berkus
This commit is contained in:
Bruce Momjian 2014-09-10 17:13:04 -04:00
parent 84aa8ba128
commit 36ad1a87a3
5 changed files with 26 additions and 2 deletions
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7
doc/src/sgml/maintenance.sgml
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@ -640,7 +640,12 @@ HINT: Stop the postmaster and vacuum that database in single-user mode.
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
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

16
src/backend/utils/adt/xid.c
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@ -16,6 +16,7 @@
#include <limits.h>
#include "access/multixact.h"
#include "access/transam.h"
#include "access/xact.h"
#include "libpq/pqformat.h"
@ -102,6 +103,21 @@ xid_age(PG_FUNCTION_ARGS)
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));
}
/*
* xidComparator
* qsort comparison function for XIDs

2
src/include/catalog/catversion.h
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@ -53,6 +53,6 @@
*/
/* yyyymmddN */
#define CATALOG_VERSION_NO 201409091
#define CATALOG_VERSION_NO 201409101
#endif

2
src/include/catalog/pg_proc.h
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@ -1279,6 +1279,8 @@ DATA(insert OID = 1180 ( abstime PGNSP PGUID 12 1 0 0 0 f f f f t f i 1 0 7
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 = 3939 ( 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_ ));

1
src/include/utils/builtins.h
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@ -845,6 +845,7 @@ extern Datum xidrecv(PG_FUNCTION_ARGS);
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);