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Add VACUUM (DISABLE_PAGE_SKIPPING) for emergencies.

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If you really want to vacuum every single page in the relation,
regardless of apparent visibility status or anything else, you can use
this option.  In previous releases, this behavior could be achieved
using VACUUM (FREEZE), but because we can now recognize all-frozen
pages as not needing to be frozen again, that no longer works.  There
should be no need for routine use of this option, but maybe bugs or
disaster recovery will necessitate its use.

Patch by me, reviewed by Andres Freund.
This commit is contained in:
Robert Haas
2016-06-17 15:48:57 -04:00
parent 20eb2731b7
commit ede62e56fb
7 changed files with 97 additions and 46 deletions
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21
doc/src/sgml/ref/vacuum.sgml
View File

@ -21,7 +21,7 @@ PostgreSQL documentation
<refsynopsisdiv>
<synopsis>
VACUUM [ ( { FULL | FREEZE | VERBOSE | ANALYZE } [, ...] ) ] [ <replaceable class="PARAMETER">table_name</replaceable> [ (<replaceable class="PARAMETER">column_name</replaceable> [, ...] ) ] ]
VACUUM [ ( { FULL | FREEZE | VERBOSE | ANALYZE | DISABLE_PAGE_SKIPPING } [, ...] ) ] [ <replaceable class="PARAMETER">table_name</replaceable> [ (<replaceable class="PARAMETER">column_name</replaceable> [, ...] ) ] ]
VACUUM [ FULL ] [ FREEZE ] [ VERBOSE ] [ <replaceable class="PARAMETER">table_name</replaceable> ]
VACUUM [ FULL ] [ FREEZE ] [ VERBOSE ] ANALYZE [ <replaceable class="PARAMETER">table_name</replaceable> [ (<replaceable class="PARAMETER">column_name</replaceable> [, ...] ) ] ]
</synopsis>
@ -129,6 +129,25 @@ VACUUM [ FULL ] [ FREEZE ] [ VERBOSE ] ANALYZE [ <replaceable class="PARAMETER">
</listitem>
</varlistentry>
<varlistentry>
<term><literal>DISABLE_PAGE_SKIPPING</literal></term>
<listitem>
<para>
Normally, <command>VACUUM</> will skip pages based on the <link
linkend="vacuum-for-visibility-map">visibility map</>. Pages where
all tuples are known to be frozen can always be skipped, and those
where all tuples are known to be visible to all transactions may be
skipped except when performing an aggressive vacuum. Furthermore,
except when performing an aggressive vacuum, some pages may be skipped
in order to avoid waiting for other sessions to finish using them.
This option disables all page-skipping behavior, and is intended to
be used only the contents of the visibility map are thought to
be suspect, which should happen only if there is a hardware or software
issue causing database corruption.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><replaceable class="PARAMETER">table_name</replaceable></term>
<listitem>

9
src/backend/commands/vacuum.c
View File

@ -185,6 +185,15 @@ vacuum(int options, RangeVar *relation, Oid relid, VacuumParams *params,
errmsg("%s cannot be executed from VACUUM or ANALYZE",
stmttype)));
/*
* Sanity check DISABLE_PAGE_SKIPPING option.
*/
if ((options & VACOPT_FULL) != 0 &&
(options & VACOPT_DISABLE_PAGE_SKIPPING) != 0)
ereport(ERROR,
(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
errmsg("VACUUM option DISABLE_PAGE_SKIPPING cannot be used with FULL")));
/*
* Send info about dead objects to the statistics collector, unless we are
* in autovacuum --- autovacuum.c does this for itself.

37
src/backend/commands/vacuumlazy.c
View File

@ -137,8 +137,9 @@ static BufferAccessStrategy vac_strategy;
/* non-export function prototypes */
static void lazy_scan_heap(Relation onerel, LVRelStats *vacrelstats,
Relation *Irel, int nindexes, bool aggressive);
static void lazy_scan_heap(Relation onerel, int options,
LVRelStats *vacrelstats, Relation *Irel, int nindexes,
bool aggressive);
static void lazy_vacuum_heap(Relation onerel, LVRelStats *vacrelstats);
static bool lazy_check_needs_freeze(Buffer buf, bool *hastup);
static void lazy_vacuum_index(Relation indrel,
@ -223,15 +224,17 @@ lazy_vacuum_rel(Relation onerel, int options, VacuumParams *params,
&MultiXactCutoff, &mxactFullScanLimit);
/*
* We request an aggressive scan if either the table's frozen Xid is now
* older than or equal to the requested Xid full-table scan limit; or if
* the table's minimum MultiXactId is older than or equal to the requested
* mxid full-table scan limit.
* We request an aggressive scan if the table's frozen Xid is now older
* than or equal to the requested Xid full-table scan limit; or if the
* table's minimum MultiXactId is older than or equal to the requested
* mxid full-table scan limit; or if DISABLE_PAGE_SKIPPING was specified.
*/
aggressive = TransactionIdPrecedesOrEquals(onerel->rd_rel->relfrozenxid,
xidFullScanLimit);
aggressive |= MultiXactIdPrecedesOrEquals(onerel->rd_rel->relminmxid,
mxactFullScanLimit);
if (options & VACOPT_DISABLE_PAGE_SKIPPING)
aggressive = true;
vacrelstats = (LVRelStats *) palloc0(sizeof(LVRelStats));
@ -246,7 +249,7 @@ lazy_vacuum_rel(Relation onerel, int options, VacuumParams *params,
vacrelstats->hasindex = (nindexes > 0);
/* Do the vacuuming */
lazy_scan_heap(onerel, vacrelstats, Irel, nindexes, aggressive);
lazy_scan_heap(onerel, options, vacrelstats, Irel, nindexes, aggressive);
/* Done with indexes */
vac_close_indexes(nindexes, Irel, NoLock);
@ -441,7 +444,7 @@ vacuum_log_cleanup_info(Relation rel, LVRelStats *vacrelstats)
* reference them have been killed.
*/
static void
lazy_scan_heap(Relation onerel, LVRelStats *vacrelstats,
lazy_scan_heap(Relation onerel, int options, LVRelStats *vacrelstats,
Relation *Irel, int nindexes, bool aggressive)
{
BlockNumber nblocks,
@ -542,9 +545,10 @@ lazy_scan_heap(Relation onerel, LVRelStats *vacrelstats,
* the last page. This is worth avoiding mainly because such a lock must
* be replayed on any hot standby, where it can be disruptive.
*/
for (next_unskippable_block = 0;
next_unskippable_block < nblocks;
next_unskippable_block++)
next_unskippable_block = 0;
if ((options & VACOPT_DISABLE_PAGE_SKIPPING) == 0)
{
while (next_unskippable_block < nblocks)
{
uint8 vmstatus;
@ -561,6 +565,8 @@ lazy_scan_heap(Relation onerel, LVRelStats *vacrelstats,
break;
}
vacuum_delay_point();
next_unskippable_block++;
}
}
if (next_unskippable_block >= SKIP_PAGES_THRESHOLD)
@ -594,9 +600,10 @@ lazy_scan_heap(Relation onerel, LVRelStats *vacrelstats,
if (blkno == next_unskippable_block)
{
/* Time to advance next_unskippable_block */
for (next_unskippable_block++;
next_unskippable_block < nblocks;
next_unskippable_block++)
next_unskippable_block++;
if ((options & VACOPT_DISABLE_PAGE_SKIPPING) == 0)
{
while (next_unskippable_block < nblocks)
{
uint8 vmskipflags;
@ -614,6 +621,8 @@ lazy_scan_heap(Relation onerel, LVRelStats *vacrelstats,
break;
}
vacuum_delay_point();
next_unskippable_block++;
}
}
/*

10
src/backend/parser/gram.y
View File

@ -9370,6 +9370,16 @@ vacuum_option_elem:
| VERBOSE { $$ = VACOPT_VERBOSE; }
| FREEZE { $$ = VACOPT_FREEZE; }
| FULL { $$ = VACOPT_FULL; }
| IDENT
{
if (strcmp($1, "disable_page_skipping") == 0)
$$ = VACOPT_DISABLE_PAGE_SKIPPING;
else
ereport(ERROR,
(errcode(ERRCODE_SYNTAX_ERROR),
errmsg("unrecognized VACUUM option \"%s\"", $1),
parser_errposition(@1)));
}
;
AnalyzeStmt:

3
src/include/nodes/parsenodes.h
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@ -2822,7 +2822,8 @@ typedef enum VacuumOption
VACOPT_FREEZE = 1 << 3, /* FREEZE option */
VACOPT_FULL = 1 << 4, /* FULL (non-concurrent) vacuum */
VACOPT_NOWAIT = 1 << 5, /* don't wait to get lock (autovacuum only) */
VACOPT_SKIPTOAST = 1 << 6 /* don't process the TOAST table, if any */
VACOPT_SKIPTOAST = 1 << 6, /* don't process the TOAST table, if any */
VACOPT_DISABLE_PAGE_SKIPPING = 1 << 7 /* don't skip any pages */
} VacuumOption;
typedef struct VacuumStmt

1
src/test/regress/expected/vacuum.out
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@ -79,5 +79,6 @@ ERROR: ANALYZE cannot be executed from VACUUM or ANALYZE
CONTEXT: SQL function "do_analyze" statement 1
SQL function "wrap_do_analyze" statement 1
VACUUM FULL vactst;
VACUUM (DISABLE_PAGE_SKIPPING) vaccluster;
DROP TABLE vaccluster;
DROP TABLE vactst;

2
src/test/regress/sql/vacuum.sql
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@ -60,5 +60,7 @@ VACUUM FULL pg_database;
VACUUM FULL vaccluster;
VACUUM FULL vactst;
VACUUM (DISABLE_PAGE_SKIPPING) vaccluster;
DROP TABLE vaccluster;
DROP TABLE vactst;