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robertmhaasrobertmhaas
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Move VM update code from lazy_scan_heap() to lazy_scan_prune().
Most of the output parameters of lazy_scan_prune() were being used to update the VM in lazy_scan_heap(). Moving that code into lazy_scan_prune() simplifies lazy_scan_heap() and requires less communication between the two. This change permits some further code simplification, but that is left for a separate commit. Melanie Plageman, reviewed by me. Discussion: http://postgr.es/m/CAAKRu_aM=OL85AOr-80wBsCr=vLVzhnaavqkVPRkFBtD0zsuLQ@mail.gmail.com
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‎src/backend/access/heap/vacuumlazy.c

Lines changed: 115 additions & 111 deletions
Original file line numberDiff line numberDiff line change
@@ -249,6 +249,7 @@ static bool lazy_scan_new_or_empty(LVRelState *vacrel, Buffer buf,
249249
bool sharelock, Buffer vmbuffer);
250250
static void lazy_scan_prune(LVRelState *vacrel, Buffer buf,
251251
BlockNumber blkno, Page page,
252+
Buffer vmbuffer, bool all_visible_according_to_vm,
252253
LVPagePruneState *prunestate);
253254
static bool lazy_scan_noprune(LVRelState *vacrel, Buffer buf,
254255
BlockNumber blkno, Page page,
@@ -1032,117 +1033,9 @@ lazy_scan_heap(LVRelState *vacrel)
10321033
* tuple headers of remaining items with storage. It also determines
10331034
* if truncating this block is safe.
10341035
*/
1035-
lazy_scan_prune(vacrel, buf, blkno, page, &prunestate);
1036-
1037-
Assert(!prunestate.all_visible || !prunestate.has_lpdead_items);
1038-
1039-
/*
1040-
* Handle setting visibility map bit based on information from the VM
1041-
* (as of last lazy_scan_skip() call), and from prunestate
1042-
*/
1043-
if (!all_visible_according_to_vm && prunestate.all_visible)
1044-
{
1045-
uint8 flags = VISIBILITYMAP_ALL_VISIBLE;
1046-
1047-
if (prunestate.all_frozen)
1048-
{
1049-
Assert(!TransactionIdIsValid(prunestate.visibility_cutoff_xid));
1050-
flags |= VISIBILITYMAP_ALL_FROZEN;
1051-
}
1052-
1053-
/*
1054-
* It should never be the case that the visibility map page is set
1055-
* while the page-level bit is clear, but the reverse is allowed
1056-
* (if checksums are not enabled). Regardless, set both bits so
1057-
* that we get back in sync.
1058-
*
1059-
* NB: If the heap page is all-visible but the VM bit is not set,
1060-
* we don't need to dirty the heap page. However, if checksums
1061-
* are enabled, we do need to make sure that the heap page is
1062-
* dirtied before passing it to visibilitymap_set(), because it
1063-
* may be logged. Given that this situation should only happen in
1064-
* rare cases after a crash, it is not worth optimizing.
1065-
*/
1066-
PageSetAllVisible(page);
1067-
MarkBufferDirty(buf);
1068-
visibilitymap_set(vacrel->rel, blkno, buf, InvalidXLogRecPtr,
1069-
vmbuffer, prunestate.visibility_cutoff_xid,
1070-
flags);
1071-
}
1072-
1073-
/*
1074-
* As of PostgreSQL 9.2, the visibility map bit should never be set if
1075-
* the page-level bit is clear. However, it's possible that the bit
1076-
* got cleared after lazy_scan_skip() was called, so we must recheck
1077-
* with buffer lock before concluding that the VM is corrupt.
1078-
*/
1079-
else if (all_visible_according_to_vm && !PageIsAllVisible(page) &&
1080-
visibilitymap_get_status(vacrel->rel, blkno, &vmbuffer) != 0)
1081-
{
1082-
elog(WARNING, "page is not marked all-visible but visibility map bit is set in relation \"%s\" page %u",
1083-
vacrel->relname, blkno);
1084-
visibilitymap_clear(vacrel->rel, blkno, vmbuffer,
1085-
VISIBILITYMAP_VALID_BITS);
1086-
}
1087-
1088-
/*
1089-
* It's possible for the value returned by
1090-
* GetOldestNonRemovableTransactionId() to move backwards, so it's not
1091-
* wrong for us to see tuples that appear to not be visible to
1092-
* everyone yet, while PD_ALL_VISIBLE is already set. The real safe
1093-
* xmin value never moves backwards, but
1094-
* GetOldestNonRemovableTransactionId() is conservative and sometimes
1095-
* returns a value that's unnecessarily small, so if we see that
1096-
* contradiction it just means that the tuples that we think are not
1097-
* visible to everyone yet actually are, and the PD_ALL_VISIBLE flag
1098-
* is correct.
1099-
*
1100-
* There should never be LP_DEAD items on a page with PD_ALL_VISIBLE
1101-
* set, however.
1102-
*/
1103-
else if (prunestate.has_lpdead_items && PageIsAllVisible(page))
1104-
{
1105-
elog(WARNING, "page containing LP_DEAD items is marked as all-visible in relation \"%s\" page %u",
1106-
vacrel->relname, blkno);
1107-
PageClearAllVisible(page);
1108-
MarkBufferDirty(buf);
1109-
visibilitymap_clear(vacrel->rel, blkno, vmbuffer,
1110-
VISIBILITYMAP_VALID_BITS);
1111-
}
1112-
1113-
/*
1114-
* If the all-visible page is all-frozen but not marked as such yet,
1115-
* mark it as all-frozen. Note that all_frozen is only valid if
1116-
* all_visible is true, so we must check both prunestate fields.
1117-
*/
1118-
else if (all_visible_according_to_vm && prunestate.all_visible &&
1119-
prunestate.all_frozen &&
1120-
!VM_ALL_FROZEN(vacrel->rel, blkno, &vmbuffer))
1121-
{
1122-
/*
1123-
* Avoid relying on all_visible_according_to_vm as a proxy for the
1124-
* page-level PD_ALL_VISIBLE bit being set, since it might have
1125-
* become stale -- even when all_visible is set in prunestate
1126-
*/
1127-
if (!PageIsAllVisible(page))
1128-
{
1129-
PageSetAllVisible(page);
1130-
MarkBufferDirty(buf);
1131-
}
1132-
1133-
/*
1134-
* Set the page all-frozen (and all-visible) in the VM.
1135-
*
1136-
* We can pass InvalidTransactionId as our visibility_cutoff_xid,
1137-
* since a snapshotConflictHorizon sufficient to make everything
1138-
* safe for REDO was logged when the page's tuples were frozen.
1139-
*/
1140-
Assert(!TransactionIdIsValid(prunestate.visibility_cutoff_xid));
1141-
visibilitymap_set(vacrel->rel, blkno, buf, InvalidXLogRecPtr,
1142-
vmbuffer, InvalidTransactionId,
1143-
VISIBILITYMAP_ALL_VISIBLE |
1144-
VISIBILITYMAP_ALL_FROZEN);
1145-
}
1036+
lazy_scan_prune(vacrel, buf, blkno, page,
1037+
vmbuffer, all_visible_according_to_vm,
1038+
&prunestate);
11461039

11471040
/*
11481041
* Final steps for block: drop cleanup lock, record free space in the
@@ -1496,6 +1389,8 @@ lazy_scan_prune(LVRelState *vacrel,
14961389
Buffer buf,
14971390
BlockNumber blkno,
14981391
Page page,
1392+
Buffer vmbuffer,
1393+
bool all_visible_according_to_vm,
14991394
LVPagePruneState *prunestate)
15001395
{
15011396
Relation rel = vacrel->rel;
@@ -1880,6 +1775,115 @@ lazy_scan_prune(LVRelState *vacrel,
18801775
/* Can't truncate this page */
18811776
if (hastup)
18821777
vacrel->nonempty_pages = blkno + 1;
1778+
1779+
Assert(!prunestate->all_visible || !prunestate->has_lpdead_items);
1780+
1781+
/*
1782+
* Handle setting visibility map bit based on information from the VM (as
1783+
* of last lazy_scan_skip() call), and from prunestate
1784+
*/
1785+
if (!all_visible_according_to_vm && prunestate->all_visible)
1786+
{
1787+
uint8 flags = VISIBILITYMAP_ALL_VISIBLE;
1788+
1789+
if (prunestate->all_frozen)
1790+
{
1791+
Assert(!TransactionIdIsValid(prunestate->visibility_cutoff_xid));
1792+
flags |= VISIBILITYMAP_ALL_FROZEN;
1793+
}
1794+
1795+
/*
1796+
* It should never be the case that the visibility map page is set
1797+
* while the page-level bit is clear, but the reverse is allowed (if
1798+
* checksums are not enabled). Regardless, set both bits so that we
1799+
* get back in sync.
1800+
*
1801+
* NB: If the heap page is all-visible but the VM bit is not set, we
1802+
* don't need to dirty the heap page. However, if checksums are
1803+
* enabled, we do need to make sure that the heap page is dirtied
1804+
* before passing it to visibilitymap_set(), because it may be logged.
1805+
* Given that this situation should only happen in rare cases after a
1806+
* crash, it is not worth optimizing.
1807+
*/
1808+
PageSetAllVisible(page);
1809+
MarkBufferDirty(buf);
1810+
visibilitymap_set(vacrel->rel, blkno, buf, InvalidXLogRecPtr,
1811+
vmbuffer, prunestate->visibility_cutoff_xid,
1812+
flags);
1813+
}
1814+
1815+
/*
1816+
* As of PostgreSQL 9.2, the visibility map bit should never be set if the
1817+
* page-level bit is clear. However, it's possible that the bit got
1818+
* cleared after lazy_scan_skip() was called, so we must recheck with
1819+
* buffer lock before concluding that the VM is corrupt.
1820+
*/
1821+
else if (all_visible_according_to_vm && !PageIsAllVisible(page) &&
1822+
visibilitymap_get_status(vacrel->rel, blkno, &vmbuffer) != 0)
1823+
{
1824+
elog(WARNING, "page is not marked all-visible but visibility map bit is set in relation \"%s\" page %u",
1825+
vacrel->relname, blkno);
1826+
visibilitymap_clear(vacrel->rel, blkno, vmbuffer,
1827+
VISIBILITYMAP_VALID_BITS);
1828+
}
1829+
1830+
/*
1831+
* It's possible for the value returned by
1832+
* GetOldestNonRemovableTransactionId() to move backwards, so it's not
1833+
* wrong for us to see tuples that appear to not be visible to everyone
1834+
* yet, while PD_ALL_VISIBLE is already set. The real safe xmin value
1835+
* never moves backwards, but GetOldestNonRemovableTransactionId() is
1836+
* conservative and sometimes returns a value that's unnecessarily small,
1837+
* so if we see that contradiction it just means that the tuples that we
1838+
* think are not visible to everyone yet actually are, and the
1839+
* PD_ALL_VISIBLE flag is correct.
1840+
*
1841+
* There should never be LP_DEAD items on a page with PD_ALL_VISIBLE set,
1842+
* however.
1843+
*/
1844+
else if (prunestate->has_lpdead_items && PageIsAllVisible(page))
1845+
{
1846+
elog(WARNING, "page containing LP_DEAD items is marked as all-visible in relation \"%s\" page %u",
1847+
vacrel->relname, blkno);
1848+
PageClearAllVisible(page);
1849+
MarkBufferDirty(buf);
1850+
visibilitymap_clear(vacrel->rel, blkno, vmbuffer,
1851+
VISIBILITYMAP_VALID_BITS);
1852+
}
1853+
1854+
/*
1855+
* If the all-visible page is all-frozen but not marked as such yet, mark
1856+
* it as all-frozen. Note that all_frozen is only valid if all_visible is
1857+
* true, so we must check both prunestate fields.
1858+
*/
1859+
else if (all_visible_according_to_vm && prunestate->all_visible &&
1860+
prunestate->all_frozen &&
1861+
!VM_ALL_FROZEN(vacrel->rel, blkno, &vmbuffer))
1862+
{
1863+
/*
1864+
* Avoid relying on all_visible_according_to_vm as a proxy for the
1865+
* page-level PD_ALL_VISIBLE bit being set, since it might have become
1866+
* stale -- even when all_visible is set in prunestate
1867+
*/
1868+
if (!PageIsAllVisible(page))
1869+
{
1870+
PageSetAllVisible(page);
1871+
MarkBufferDirty(buf);
1872+
}
1873+
1874+
/*
1875+
* Set the page all-frozen (and all-visible) in the VM.
1876+
*
1877+
* We can pass InvalidTransactionId as our visibility_cutoff_xid,
1878+
* since a snapshotConflictHorizon sufficient to make everything safe
1879+
* for REDO was logged when the page's tuples were frozen.
1880+
*/
1881+
Assert(!TransactionIdIsValid(prunestate->visibility_cutoff_xid));
1882+
visibilitymap_set(vacrel->rel, blkno, buf, InvalidXLogRecPtr,
1883+
vmbuffer, InvalidTransactionId,
1884+
VISIBILITYMAP_ALL_VISIBLE |
1885+
VISIBILITYMAP_ALL_FROZEN);
1886+
}
18831887
}
18841888

18851889
/*

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