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Don't vacuum all-frozen pages.

Browse Source 
Commit a892234f83 gave us enough
infrastructure to avoid vacuuming pages where every tuple on the
page is already frozen.  So, replace the notion of a scan_all or
whole-table vacuum with the less onerous notion of an "aggressive"
vacuum, which will pages that are all-visible, but still skip those
that are all-frozen.

This should greatly reduce the cost of anti-wraparound vacuuming
on large clusters where the majority of data is never touched
between one cycle and the next, because we'll no longer have to
read all of those pages only to find out that we don't need to
do anything with them.

Patch by me, reviewed by Masahiko Sawada.
pull/11/head
Robert Haas 10 years ago
parent 364a9f47ab
commit fd31cd2651
3 changed files with 196 additions and 119 deletions
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  1. 20
      doc/src/sgml/config.sgml
  2. 86
      doc/src/sgml/maintenance.sgml
  3. 209
      src/backend/commands/vacuumlazy.c

20
doc/src/sgml/config.sgml
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@ -5984,12 +5984,15 @@ COPY postgres_log FROM '/full/path/to/logfile.csv' WITH csv;
</term>
<listitem>
<para>
<command>VACUUM</> performs a whole-table scan if the table's
<command>VACUUM</> performs an aggressive scan if the table's
<structname>pg_class</>.<structfield>relfrozenxid</> field has reached
the age specified by this setting. The default is 150 million
transactions. Although users can set this value anywhere from zero to
two billions, <command>VACUUM</> will silently limit the effective value
to 95% of <xref linkend="guc-autovacuum-freeze-max-age">, so that a
the age specified by this setting. An aggressive scan differs from
a regular <command>VACUUM</> in that it visits every page that might
contain unfrozen XIDs or MXIDs, not just those that might contain dead
tuples. The default is 150 million transactions. Although users can
set this value anywhere from zero to two billions, <command>VACUUM</>
will silently limit the effective value to 95% of
<xref linkend="guc-autovacuum-freeze-max-age">, so that a
periodical manual <command>VACUUM</> has a chance to run before an
anti-wraparound autovacuum is launched for the table. For more
information see
@ -6028,9 +6031,12 @@ COPY postgres_log FROM '/full/path/to/logfile.csv' WITH csv;
</term>
<listitem>
<para>
<command>VACUUM</> performs a whole-table scan if the table's
<command>VACUUM</> performs an aggressive scan if the table's
<structname>pg_class</>.<structfield>relminmxid</> field has reached
the age specified by this setting. The default is 150 million multixacts.
the age specified by this setting. An aggressive scan differs from
a regular <command>VACUUM</> in that it visits every page that might
contain unfrozen XIDs or MXIDs, not just those that might contain dead
tuples. The default is 150 million multixacts.
Although users can set this value anywhere from zero to two billions,
<command>VACUUM</> will silently limit the effective value to 95% of
<xref linkend="guc-autovacuum-multixact-freeze-max-age">, so that a

86
doc/src/sgml/maintenance.sgml
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@ -438,22 +438,27 @@
</para>
<para>
<command>VACUUM</> normally skips pages that don't have any dead row
versions, but those pages might still have row versions with old XID
values. To ensure all old row versions have been frozen, a
scan of the whole table is needed.
<xref linkend="guc-vacuum-freeze-table-age"> controls when
<command>VACUUM</> does that: a whole table sweep is forced if
the table hasn't been fully scanned for <varname>vacuum_freeze_table_age</>
minus <varname>vacuum_freeze_min_age</> transactions. Setting it to 0
forces <command>VACUUM</> to always scan all pages, effectively ignoring
the visibility map.
<command>VACUUM</> uses the <link linkend="storage-vm">visibility map</>
to determine which pages of a relation must be scanned. Normally, it
will skips pages that don't have any dead row versions even if those pages
might still have row versions with old XID values. Therefore, normal
scans won't succeed in freezing every row version in the table.
Periodically, <command>VACUUM</> will perform an <firstterm>aggressive
vacuum</>, skipping only those pages which contain neither dead rows nor
any unfrozen XID or MXID values.
<xref linkend="guc-vacuum-freeze-table-age">
controls when <command>VACUUM</> does that: all-visible but not all-frozen
pages are scanned if the number of transactions that have passed since the
last such scan is greater than <varname>vacuum_freeze_table_age</> minus
<varname>vacuum_freeze_min_age</>. Setting
<varname>vacuum_freeze_table_age</> to 0 forces <command>VACUUM</> to
use this more aggressive strategy for all scans.
</para>
<para>
The maximum time that a table can go unvacuumed is two billion
transactions minus the <varname>vacuum_freeze_min_age</> value at
the time <command>VACUUM</> last scanned the whole table. If it were to go
the time of the last aggressive vacuum. If it were to go
unvacuumed for longer than
that, data loss could result. To ensure that this does not happen,
autovacuum is invoked on any table that might contain unfrozen rows with
@ -491,7 +496,7 @@
normal delete and update activity is run in that window. Setting it too
close could lead to anti-wraparound autovacuums, even though the table
was recently vacuumed to reclaim space, whereas lower values lead to more
frequent whole-table scans.
frequent aggressive vacuuming.
</para>
<para>
@ -527,7 +532,7 @@
<structname>pg_database</>. In particular,
the <structfield>relfrozenxid</> column of a table's
<structname>pg_class</> row contains the freeze cutoff XID that was used
by the last whole-table <command>VACUUM</> for that table. All rows
by the last aggressive <command>VACUUM</> for that table. All rows
inserted by transactions with XIDs older than this cutoff XID are
guaranteed to have been frozen. Similarly,
the <structfield>datfrozenxid</> column of a database's
@ -552,20 +557,23 @@ SELECT datname, age(datfrozenxid) FROM pg_database;
</para>
<para>
<command>VACUUM</> normally
only scans pages that have been modified since the last vacuum, but
<structfield>relfrozenxid</> can only be advanced when the whole table is
scanned. The whole table is scanned when <structfield>relfrozenxid</> is
more than <varname>vacuum_freeze_table_age</> transactions old, when
<command>VACUUM</>'s <literal>FREEZE</> option is used, or when all pages
happen to
<command>VACUUM</> normally only scans pages that have been modified
since the last vacuum, but <structfield>relfrozenxid</> can only be
advanced when every page of the table
that might contain unfrozen XIDs is scanned. This happens when
<structfield>relfrozenxid</> is more than
<varname>vacuum_freeze_table_age</> transactions old, when
<command>VACUUM</>'s <literal>FREEZE</> option is used, or when all
pages that are not already all-frozen happen to
require vacuuming to remove dead row versions. When <command>VACUUM</>
scans the whole table, after it's finished <literal>age(relfrozenxid)</>
should be a little more than the <varname>vacuum_freeze_min_age</> setting
that was used (more by the number of transactions started since the
<command>VACUUM</> started). If no whole-table-scanning <command>VACUUM</>
is issued on the table until <varname>autovacuum_freeze_max_age</> is
reached, an autovacuum will soon be forced for the table.
scans every page in the table that is not already all-frozen, it should
set <literal>age(relfrozenxid)</> to a value just a little more than the
<varname>vacuum_freeze_min_age</> setting
that was used (more by the number of transcations started since the
<command>VACUUM</> started). If no <structfield>relfrozenxid</>-advancing
<command>VACUUM</> is issued on the table until
<varname>autovacuum_freeze_max_age</> is reached, an autovacuum will soon
be forced for the table.
</para>
<para>
@ -634,21 +642,23 @@ HINT: Stop the postmaster and vacuum that database in single-user mode.
</para>
<para>
During a <command>VACUUM</> table scan, either partial or of the whole
table, any multixact ID older than
Whenever <command>VACUUM</> scans any part of a table, it will replace
any multixact ID it encounters which is older than
<xref linkend="guc-vacuum-multixact-freeze-min-age">
is replaced by a different value, which can be the zero value, a single
by a different value, which can be the zero value, a single
transaction ID, or a newer multixact ID. For each table,
<structname>pg_class</>.<structfield>relminmxid</> stores the oldest
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
<xref linkend="guc-vacuum-multixact-freeze-table-age">, an aggressive
vacuum is forced. As discussed in the previous section, an aggressive
vacuum means that only those pages which are known to be all-frozen will
be skipped. <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
Aggressive <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
@ -656,13 +666,13 @@ HINT: Stop the postmaster and vacuum that database in single-user mode.
</para>
<para>
As a safety device, a whole-table vacuum scan will occur for any table
As a safety device, an aggressive vacuum scan will occur for any table
whose multixact-age is greater than
<xref linkend="guc-autovacuum-multixact-freeze-max-age">. Whole-table
<xref linkend="guc-autovacuum-multixact-freeze-max-age">. Aggressive
vacuum scans will also occur progressively for all tables, starting with
those that have the oldest multixact-age, if the amount of used member
storage space exceeds the amount 50% of the addressable storage space.
Both of these kinds of whole-table scans will occur even if autovacuum is
Both of these kinds of aggressive scans will occur even if autovacuum is
nominally disabled.
</para>
</sect3>
@ -743,9 +753,9 @@ vacuum threshold = vacuum base threshold + vacuum scale factor * number of tuple
<command>UPDATE</command> and <command>DELETE</command> operation. (It
is only semi-accurate because some information might be lost under heavy
load.) If the <structfield>relfrozenxid</> value of the table is more
than <varname>vacuum_freeze_table_age</> transactions old, the whole
table is scanned to freeze old tuples and advance
<structfield>relfrozenxid</>, otherwise only pages that have been modified
than <varname>vacuum_freeze_table_age</> transactions old, an aggressive
vacuum is performed to freeze old tuples and advance
<structfield>relfrozenxid</>; otherwise, only pages that have been modified
since the last vacuum are scanned.
</para>

209
src/backend/commands/vacuumlazy.c
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@ -106,6 +106,7 @@ typedef struct LVRelStats
BlockNumber rel_pages; /* total number of pages */
BlockNumber scanned_pages; /* number of pages we examined */
BlockNumber pinskipped_pages; /* # of pages we skipped due to a pin */
BlockNumber frozenskipped_pages; /* # of frozen pages we skipped */
double scanned_tuples; /* counts only tuples on scanned pages */
double old_rel_tuples; /* previous value of pg_class.reltuples */
double new_rel_tuples; /* new estimated total # of tuples */
@ -136,7 +137,7 @@ static BufferAccessStrategy vac_strategy;
/* non-export function prototypes */
static void lazy_scan_heap(Relation onerel, LVRelStats *vacrelstats,
Relation *Irel, int nindexes, bool scan_all);
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,
@ -182,8 +183,8 @@ lazy_vacuum_rel(Relation onerel, int options, VacuumParams *params,
int usecs;
double read_rate,
write_rate;
bool scan_all; /* should we scan all pages? */
bool scanned_all; /* did we actually scan all pages? */
bool aggressive; /* should we scan all unfrozen pages? */
bool scanned_all_unfrozen; /* actually scanned all such pages? */
TransactionId xidFullScanLimit;
MultiXactId mxactFullScanLimit;
BlockNumber new_rel_pages;
@ -221,15 +222,15 @@ lazy_vacuum_rel(Relation onerel, int options, VacuumParams *params,
&MultiXactCutoff, &mxactFullScanLimit);
/*
* We request a full 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
* 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.
*/
scan_all = TransactionIdPrecedesOrEquals(onerel->rd_rel->relfrozenxid,
xidFullScanLimit);
scan_all |= MultiXactIdPrecedesOrEquals(onerel->rd_rel->relminmxid,
mxactFullScanLimit);
aggressive = TransactionIdPrecedesOrEquals(onerel->rd_rel->relfrozenxid,
xidFullScanLimit);
aggressive |= MultiXactIdPrecedesOrEquals(onerel->rd_rel->relminmxid,
mxactFullScanLimit);
vacrelstats = (LVRelStats *) palloc0(sizeof(LVRelStats));
@ -244,7 +245,7 @@ lazy_vacuum_rel(Relation onerel, int options, VacuumParams *params,
vacrelstats->hasindex = (nindexes > 0);
/* Do the vacuuming */
lazy_scan_heap(onerel, vacrelstats, Irel, nindexes, scan_all);
lazy_scan_heap(onerel, vacrelstats, Irel, nindexes, aggressive);
/* Done with indexes */
vac_close_indexes(nindexes, Irel, NoLock);
@ -256,13 +257,14 @@ lazy_vacuum_rel(Relation onerel, int options, VacuumParams *params,
* NB: We need to check this before truncating the relation, because that
* will change ->rel_pages.
*/
if (vacrelstats->scanned_pages < vacrelstats->rel_pages)
if ((vacrelstats->scanned_pages + vacrelstats->frozenskipped_pages)
< vacrelstats->rel_pages)
{
Assert(!scan_all);
scanned_all = false;
Assert(!aggressive);
scanned_all_unfrozen = false;
}
else
scanned_all = true;
scanned_all_unfrozen = true;
/*
* Optionally truncate the relation.
@ -302,8 +304,8 @@ lazy_vacuum_rel(Relation onerel, int options, VacuumParams *params,
if (new_rel_allvisible > new_rel_pages)
new_rel_allvisible = new_rel_pages;
new_frozen_xid = scanned_all ? FreezeLimit : InvalidTransactionId;
new_min_multi = scanned_all ? MultiXactCutoff : InvalidMultiXactId;
new_frozen_xid = scanned_all_unfrozen ? FreezeLimit : InvalidTransactionId;
new_min_multi = scanned_all_unfrozen ? MultiXactCutoff : InvalidMultiXactId;
vac_update_relstats(onerel,
new_rel_pages,
@ -358,10 +360,11 @@ lazy_vacuum_rel(Relation onerel, int options, VacuumParams *params,
get_namespace_name(RelationGetNamespace(onerel)),
RelationGetRelationName(onerel),
vacrelstats->num_index_scans);
appendStringInfo(&buf, _("pages: %u removed, %u remain, %u skipped due to pins\n"),
appendStringInfo(&buf, _("pages: %u removed, %u remain, %u skipped due to pins, %u skipped frozen\n"),
vacrelstats->pages_removed,
vacrelstats->rel_pages,
vacrelstats->pinskipped_pages);
vacrelstats->pinskipped_pages,
vacrelstats->frozenskipped_pages);
appendStringInfo(&buf,
_("tuples: %.0f removed, %.0f remain, %.0f are dead but not yet removable\n"),
vacrelstats->tuples_deleted,
@ -434,7 +437,7 @@ vacuum_log_cleanup_info(Relation rel, LVRelStats *vacrelstats)
*/
static void
lazy_scan_heap(Relation onerel, LVRelStats *vacrelstats,
Relation *Irel, int nindexes, bool scan_all)
Relation *Irel, int nindexes, bool aggressive)
{
BlockNumber nblocks,
blkno;
@ -450,8 +453,8 @@ lazy_scan_heap(Relation onerel, LVRelStats *vacrelstats,
int i;
PGRUsage ru0;
Buffer vmbuffer = InvalidBuffer;
BlockNumber next_not_all_visible_block;
bool skipping_all_visible_blocks;
BlockNumber next_unskippable_block;
bool skipping_blocks;
xl_heap_freeze_tuple *frozen;
StringInfoData buf;
@ -479,35 +482,39 @@ lazy_scan_heap(Relation onerel, LVRelStats *vacrelstats,
frozen = palloc(sizeof(xl_heap_freeze_tuple) * MaxHeapTuplesPerPage);
/*
* We want to skip pages that don't require vacuuming according to the
* visibility map, but only when we can skip at least SKIP_PAGES_THRESHOLD
* consecutive pages. Since we're reading sequentially, the OS should be
* doing readahead for us, so there's no gain in skipping a page now and
* then; that's likely to disable readahead and so be counterproductive.
* Also, skipping even a single page means that we can't update
* relfrozenxid, so we only want to do it if we can skip a goodly number
* of pages.
* Except when aggressive is set, we want to skip pages that are
* all-visible according to the visibility map, but only when we can skip
* at least SKIP_PAGES_THRESHOLD consecutive pages. Since we're reading
* sequentially, the OS should be doing readahead for us, so there's no
* gain in skipping a page now and then; that's likely to disable
* readahead and so be counterproductive. Also, skipping even a single
* page means that we can't update relfrozenxid, so we only want to do it
* if we can skip a goodly number of pages.
*
* Before entering the main loop, establish the invariant that
* next_not_all_visible_block is the next block number >= blkno that's not
* all-visible according to the visibility map, or nblocks if there's no
* such block. Also, we set up the skipping_all_visible_blocks flag,
* which is needed because we need hysteresis in the decision: once we've
* started skipping blocks, we may as well skip everything up to the next
* not-all-visible block.
* When aggressive is set, we can't skip pages just because they are
* all-visible, but we can still skip pages that are all-frozen, since
* such pages do not need freezing and do not affect the value that we can
* safely set for relfrozenxid or relminmxid.
*
* Note: if scan_all is true, we won't actually skip any pages; but we
* maintain next_not_all_visible_block anyway, so as to set up the
* all_visible_according_to_vm flag correctly for each page.
* Before entering the main loop, establish the invariant that
* next_unskippable_block is the next block number >= blkno that's not we
* can't skip based on the visibility map, either all-visible for a
* regular scan or all-frozen for an aggressive scan. We set it to
* nblocks if there's no such block. We also set up the skipping_blocks
* flag correctly at this stage.
*
* Note: The value returned by visibilitymap_get_status could be slightly
* out-of-date, since we make this test before reading the corresponding
* heap page or locking the buffer. This is OK. If we mistakenly think
* that the page is all-visible when in fact the flag's just been cleared,
* we might fail to vacuum the page. But it's OK to skip pages when
* scan_all is not set, so no great harm done; the next vacuum will find
* them. If we make the reverse mistake and vacuum a page unnecessarily,
* it'll just be a no-op.
* that the page is all-visible or all-frozen when in fact the flag's just
* been cleared, we might fail to vacuum the page. It's easy to see that
* skipping a page when aggressive is not set is not a very big deal; we
* might leave some dead tuples lying around, but the next vacuum will
* find them. But even when aggressive *is* set, it's still OK if we miss
* a page whose all-frozen marking has just been cleared. Any new XIDs
* just added to that page are necessarily newer than the GlobalXmin we
* computed, so they'll have no effect on the value to which we can safely
* set relfrozenxid. A similar argument applies for MXIDs and relminmxid.
*
* We will scan the table's last page, at least to the extent of
* determining whether it has tuples or not, even if it should be skipped
@ -518,18 +525,31 @@ 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_not_all_visible_block = 0;
next_not_all_visible_block < nblocks;
next_not_all_visible_block++)
for (next_unskippable_block = 0;
next_unskippable_block < nblocks;
next_unskippable_block++)
{
if (!VM_ALL_VISIBLE(onerel, next_not_all_visible_block, &vmbuffer))
break;
uint8 vmstatus;
vmstatus = visibilitymap_get_status(onerel, next_unskippable_block,
&vmbuffer);
if (aggressive)
{
if ((vmstatus & VISIBILITYMAP_ALL_FROZEN) == 0)
break;
}
else
{
if ((vmstatus & VISIBILITYMAP_ALL_VISIBLE) == 0)
break;
}
vacuum_delay_point();
}
if (next_not_all_visible_block >= SKIP_PAGES_THRESHOLD)
skipping_all_visible_blocks = true;
if (next_unskippable_block >= SKIP_PAGES_THRESHOLD)
skipping_blocks = true;
else
skipping_all_visible_blocks = false;
skipping_blocks = false;
for (blkno = 0; blkno < nblocks; blkno++)
{
@ -542,7 +562,7 @@ lazy_scan_heap(Relation onerel, LVRelStats *vacrelstats,
int prev_dead_count;
int nfrozen;
Size freespace;
bool all_visible_according_to_vm;
bool all_visible_according_to_vm = false;
bool all_visible;
bool all_frozen = true; /* provided all_visible is also true */
bool has_dead_tuples;
@ -552,15 +572,28 @@ lazy_scan_heap(Relation onerel, LVRelStats *vacrelstats,
#define FORCE_CHECK_PAGE() \
(blkno == nblocks - 1 && should_attempt_truncation(vacrelstats))
if (blkno == next_not_all_visible_block)
if (blkno == next_unskippable_block)
{
/* Time to advance next_not_all_visible_block */
for (next_not_all_visible_block++;
next_not_all_visible_block < nblocks;
next_not_all_visible_block++)
/* Time to advance next_unskippable_block */
for (next_unskippable_block++;
next_unskippable_block < nblocks;
next_unskippable_block++)
{
if (!VM_ALL_VISIBLE(onerel, next_not_all_visible_block, &vmbuffer))
break;
uint8 vmskipflags;
vmskipflags = visibilitymap_get_status(onerel,
next_unskippable_block,
&vmbuffer);
if (aggressive)
{
if ((vmskipflags & VISIBILITYMAP_ALL_FROZEN) == 0)
break;
}
else
{
if ((vmskipflags & VISIBILITYMAP_ALL_VISIBLE) == 0)
break;
}
vacuum_delay_point();
}
@ -569,17 +602,44 @@ lazy_scan_heap(Relation onerel, LVRelStats *vacrelstats,
* skipping_all_visible_blocks to do the right thing at the
* following blocks.
*/
if (next_not_all_visible_block - blkno > SKIP_PAGES_THRESHOLD)
skipping_all_visible_blocks = true;
if (next_unskippable_block - blkno > SKIP_PAGES_THRESHOLD)
skipping_blocks = true;
else
skipping_all_visible_blocks = false;
all_visible_according_to_vm = false;
skipping_blocks = false;
/*
* Normally, the fact that we can't skip this block must mean that
* it's not all-visible. But in an aggressive vacuum we know only
* that it's not all-frozen, so it might still be all-visible.
*/
if (aggressive && VM_ALL_VISIBLE(onerel, blkno, &vmbuffer))
all_visible_according_to_vm = true;
}
else
{
/* Current block is all-visible */
if (skipping_all_visible_blocks && !scan_all && !FORCE_CHECK_PAGE())
/*
* The current block is potentially skippable; if we've seen a
* long enough run of skippable blocks to justify skipping it, and
* we're not forced to check it, then go ahead and skip.
* Otherwise, the page must be at least all-visible if not
* all-frozen, so we can set all_visible_according_to_vm = true.
*/
if (skipping_blocks && !FORCE_CHECK_PAGE())
{
/*
* Tricky, tricky. If this is in aggressive vacuum, the page
* must have been all-frozen at the time we checked whether it
* was skippable, but it might not be any more. We must be
* careful to count it as a skipped all-frozen page in that
* case, or else we'll think we can't update relfrozenxid and
* relminmxid. If it's not an aggressive vacuum, we don't
* know whether it was all-frozen, so we have to recheck; but
* in this case an approximate answer is OK.
*/
if (aggressive || VM_ALL_FROZEN(onerel, blkno, &vmbuffer))
vacrelstats->frozenskipped_pages++;
continue;
}
all_visible_according_to_vm = true;
}
@ -628,9 +688,10 @@ lazy_scan_heap(Relation onerel, LVRelStats *vacrelstats,
* Pin the visibility map page in case we need to mark the page
* all-visible. In most cases this will be very cheap, because we'll
* already have the correct page pinned anyway. However, it's
* possible that (a) next_not_all_visible_block is covered by a
* different VM page than the current block or (b) we released our pin
* and did a cycle of index vacuuming.
* possible that (a) next_unskippable_block is covered by a different
* VM page than the current block or (b) we released our pin and did a
* cycle of index vacuuming.
*
*/
visibilitymap_pin(onerel, blkno, &vmbuffer);
@ -641,12 +702,12 @@ lazy_scan_heap(Relation onerel, LVRelStats *vacrelstats,
if (!ConditionalLockBufferForCleanup(buf))
{
/*
* If we're not scanning the whole relation to guard against XID
* If we're not performing an aggressive scan to guard against XID
* wraparound, and we don't want to forcibly check the page, then
* it's OK to skip vacuuming pages we get a lock conflict on. They
* will be dealt with in some future vacuum.
*/
if (!scan_all && !FORCE_CHECK_PAGE())
if (!aggressive && !FORCE_CHECK_PAGE())
{
ReleaseBuffer(buf);
vacrelstats->pinskipped_pages++;
@ -663,7 +724,7 @@ lazy_scan_heap(Relation onerel, LVRelStats *vacrelstats,
* ourselves for multiple buffers and then service whichever one
* is received first. For now, this seems good enough.
*
* If we get here with scan_all false, then we're just forcibly
* If we get here with aggressive false, then we're just forcibly
* checking the page, and so we don't want to insist on getting
* the lock; we only need to know if the page contains tuples, so
* that we can update nonempty_pages correctly. It's convenient
@ -679,7 +740,7 @@ lazy_scan_heap(Relation onerel, LVRelStats *vacrelstats,
vacrelstats->nonempty_pages = blkno + 1;
continue;
}
if (!scan_all)
if (!aggressive)
{
/*
* Here, we must not advance scanned_pages; that would amount

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