Gregory Stark wrote:
Heikki Linnakangas <[EMAIL PROTECTED]> writes:
Gregory Stark wrote:
Heikki Linnakangas <[EMAIL PROTECTED]> writes:
Hmm. It just occurred to me that I think this circumvented the anti-wraparound
vacuuming: a normal vacuum doesn't advance relfrozenxid anymore. We'll need to
disable the skipping when autovacuum is triggered to prevent wraparound. VACUUM
FREEZE does that already, but it's unnecessarily aggressive in freezing.
FWIW, it seems the omission is actually the other way 'round. Autovacuum always
forces a full-scanning vacuum, making the visibility map useless for
autovacuum. This obviously needs to be fixed.
How does it do that? Is there some option in the VacStmt to control this? Do
we just need a syntax to set that option?
The way it works now is that if VacuumStmt->freeze_min_age is not -1
(which means "use the default"), the visibility map is not used and the
whole table is scanned. Autovacuum always sets freeze_min_age, so it's
never using the visibility map. Attached is a patch I'm considering to
fix that.
How easy is it to tell what percentage of the table needs to be vacuumed? If
it's > 50% perhaps it would make sense to scan the whole table? (Hm. Not
really if it's a contiguous 50% though...)
Hmm. You could scan the visibility map to see how much you could skip by
using it. You could account for contiguity.
Another idea: Perhaps each page of the visibility map should have a frozenxid
(or multiple frozenxids?). Then if an individual page of the visibility map is
old we could force scanning all the heap pages covered by that map page and
update it. I'm not sure we can do that safely though without locking issues --
or is it ok because it's vacuum doing the updating?
We discussed that a while ago:
http://archives.postgresql.org/message-id/[EMAIL PROTECTED]
Tom was concerned about making the visibility map not just a hint but
critical data. Rightly so. This is certainly 8.5 stuff; perhaps it would
be more palatable after we get the index-only-scans working using the
visibility map, since the map would be critical data anyway.
--
Heikki Linnakangas
EnterpriseDB http://www.enterprisedb.com
diff --git a/src/backend/commands/vacuumlazy.c b/src/backend/commands/vacuumlazy.c
index fd2429a..3e3cb9d 100644
--- a/src/backend/commands/vacuumlazy.c
+++ b/src/backend/commands/vacuumlazy.c
@@ -171,10 +171,7 @@ lazy_vacuum_rel(Relation onerel, VacuumStmt *vacstmt,
vacrelstats->hasindex = (nindexes > 0);
/* Should we use the visibility map or scan all pages? */
- if (vacstmt->freeze_min_age != -1)
- scan_all = true;
- else
- scan_all = false;
+ scan_all = vacstmt->scan_all;
/* Do the vacuuming */
lazy_scan_heap(onerel, vacrelstats, Irel, nindexes, scan_all);
diff --git a/src/backend/nodes/copyfuncs.c b/src/backend/nodes/copyfuncs.c
index eb7ab4d..2781f6e 100644
--- a/src/backend/nodes/copyfuncs.c
+++ b/src/backend/nodes/copyfuncs.c
@@ -2771,6 +2771,7 @@ _copyVacuumStmt(VacuumStmt *from)
COPY_SCALAR_FIELD(analyze);
COPY_SCALAR_FIELD(verbose);
COPY_SCALAR_FIELD(freeze_min_age);
+ COPY_SCALAR_FIELD(scan_all));
COPY_NODE_FIELD(relation);
COPY_NODE_FIELD(va_cols);
diff --git a/src/backend/nodes/equalfuncs.c b/src/backend/nodes/equalfuncs.c
index d4c57bb..86a032f 100644
--- a/src/backend/nodes/equalfuncs.c
+++ b/src/backend/nodes/equalfuncs.c
@@ -1436,6 +1436,7 @@ _equalVacuumStmt(VacuumStmt *a, VacuumStmt *b)
COMPARE_SCALAR_FIELD(analyze);
COMPARE_SCALAR_FIELD(verbose);
COMPARE_SCALAR_FIELD(freeze_min_age);
+ COMPARE_SCALAR_FIELD(scan_all);
COMPARE_NODE_FIELD(relation);
COMPARE_NODE_FIELD(va_cols);
diff --git a/src/backend/parser/gram.y b/src/backend/parser/gram.y
index 85f4616..1aab75c 100644
--- a/src/backend/parser/gram.y
+++ b/src/backend/parser/gram.y
@@ -5837,6 +5837,7 @@ VacuumStmt: VACUUM opt_full opt_freeze opt_verbose
n->analyze = false;
n->full = $2;
n->freeze_min_age = $3 ? 0 : -1;
+ n->scan_all = $3;
n->verbose = $4;
n->relation = NULL;
n->va_cols = NIL;
@@ -5849,6 +5850,7 @@ VacuumStmt: VACUUM opt_full opt_freeze opt_verbose
n->analyze = false;
n->full = $2;
n->freeze_min_age = $3 ? 0 : -1;
+ n->scan_all = $3;
n->verbose = $4;
n->relation = $5;
n->va_cols = NIL;
@@ -5860,6 +5862,7 @@ VacuumStmt: VACUUM opt_full opt_freeze opt_verbose
n->vacuum = true;
n->full = $2;
n->freeze_min_age = $3 ? 0 : -1;
+ n->scan_all = $3;
n->verbose |= $4;
$$ = (Node *)n;
}
diff --git a/src/backend/postmaster/autovacuum.c b/src/backend/postmaster/autovacuum.c
index 8d8947f..2c68779 100644
--- a/src/backend/postmaster/autovacuum.c
+++ b/src/backend/postmaster/autovacuum.c
@@ -2649,6 +2649,7 @@ autovacuum_do_vac_analyze(autovac_table *tab,
vacstmt.full = false;
vacstmt.analyze = tab->at_doanalyze;
vacstmt.freeze_min_age = tab->at_freeze_min_age;
+ vacstmt.scan_all = tab->at_wraparound;
vacstmt.verbose = false;
vacstmt.relation = NULL; /* not used since we pass a relid */
vacstmt.va_cols = NIL;
diff --git a/src/include/nodes/parsenodes.h b/src/include/nodes/parsenodes.h
index bb71ac1..df19f7e 100644
--- a/src/include/nodes/parsenodes.h
+++ b/src/include/nodes/parsenodes.h
@@ -1966,6 +1966,7 @@ typedef struct VacuumStmt
bool full; /* do FULL (non-concurrent) vacuum */
bool analyze; /* do ANALYZE step */
bool verbose; /* print progress info */
+ bool scan_all; /* force scan of all pages */
int freeze_min_age; /* min freeze age, or -1 to use default */
RangeVar *relation; /* single table to process, or NULL */
List *va_cols; /* list of column names, or NIL for all */
--
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