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Optimize vacuuming of relations with no indexes.

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If there are no indexes on a relation, items can be marked LP_UNUSED
instead of LP_DEAD when pruning. This significantly reduces WAL
volume, since we no longer need to emit one WAL record for pruning
and a second to change the LP_DEAD line pointers thus created to
LP_UNUSED.

Melanie Plageman, reviewed by Andres Freund, Peter Geoghegan, and me

Discussion: https://postgr.es/m/CAAKRu_bgvb_k0gKOXWzNKWHt560R0smrGe3E8zewKPs8fiMKkw%40mail.gmail.com
This commit is contained in:
Robert Haas
2024-01-18 10:03:42 -05:00
parent 7b1dbf0a8d
commit c120550edb
3 changed files with 108 additions and 102 deletions
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129
src/backend/access/heap/vacuumlazy.c
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@ -1036,69 +1036,6 @@ lazy_scan_heap(LVRelState *vacrel)
Assert(!prunestate.all_visible || !prunestate.has_lpdead_items);
if (vacrel->nindexes == 0)
{
/*
* Consider the need to do page-at-a-time heap vacuuming when
* using the one-pass strategy now.
*
* The one-pass strategy will never call lazy_vacuum(). The steps
* performed here can be thought of as the one-pass equivalent of
* a call to lazy_vacuum().
*/
if (prunestate.has_lpdead_items)
{
Size freespace;
lazy_vacuum_heap_page(vacrel, blkno, buf, 0, vmbuffer);
/* Forget the LP_DEAD items that we just vacuumed */
dead_items->num_items = 0;
/*
* Now perform FSM processing for blkno, and move on to next
* page.
*
* Our call to lazy_vacuum_heap_page() will have considered if
* it's possible to set all_visible/all_frozen independently
* of lazy_scan_prune(). Note that prunestate was invalidated
* by lazy_vacuum_heap_page() call.
*/
freespace = PageGetHeapFreeSpace(page);
UnlockReleaseBuffer(buf);
RecordPageWithFreeSpace(vacrel->rel, blkno, freespace);
/*
* Periodically perform FSM vacuuming to make newly-freed
* space visible on upper FSM pages. FreeSpaceMapVacuumRange()
* vacuums the portion of the freespace map covering heap
* pages from start to end - 1. Include the block we just
* vacuumed by passing it blkno + 1. Overflow isn't an issue
* because MaxBlockNumber + 1 is InvalidBlockNumber which
* causes FreeSpaceMapVacuumRange() to vacuum freespace map
* pages covering the remainder of the relation.
*/
if (blkno - next_fsm_block_to_vacuum >= VACUUM_FSM_EVERY_PAGES)
{
FreeSpaceMapVacuumRange(vacrel->rel, next_fsm_block_to_vacuum,
blkno + 1);
next_fsm_block_to_vacuum = blkno + 1;
}
continue;
}
/*
* There was no call to lazy_vacuum_heap_page() because pruning
* didn't encounter/create any LP_DEAD items that needed to be
* vacuumed. Prune state has not been invalidated, so proceed
* with prunestate-driven visibility map and FSM steps (just like
* the two-pass strategy).
*/
Assert(dead_items->num_items == 0);
}
/*
* Handle setting visibility map bit based on information from the VM
* (as of last lazy_scan_skip() call), and from prunestate
@ -1209,38 +1146,45 @@ lazy_scan_heap(LVRelState *vacrel)
/*
* Final steps for block: drop cleanup lock, record free space in the
* FSM
* FSM.
*
* If we will likely do index vacuuming, wait until
* lazy_vacuum_heap_rel() to save free space. This doesn't just save
* us some cycles; it also allows us to record any additional free
* space that lazy_vacuum_heap_page() will make available in cases
* where it's possible to truncate the page's line pointer array.
*
* Note: It's not in fact 100% certain that we really will call
* lazy_vacuum_heap_rel() -- lazy_vacuum() might yet opt to skip index
* vacuuming (and so must skip heap vacuuming). This is deemed okay
* because it only happens in emergencies, or when there is very
* little free space anyway. (Besides, we start recording free space
* in the FSM once index vacuuming has been abandoned.)
*/
if (prunestate.has_lpdead_items && vacrel->do_index_vacuuming)
{
/*
* Wait until lazy_vacuum_heap_rel() to save free space. This
* doesn't just save us some cycles; it also allows us to record
* any additional free space that lazy_vacuum_heap_page() will
* make available in cases where it's possible to truncate the
* page's line pointer array.
*
* Note: It's not in fact 100% certain that we really will call
* lazy_vacuum_heap_rel() -- lazy_vacuum() might yet opt to skip
* index vacuuming (and so must skip heap vacuuming). This is
* deemed okay because it only happens in emergencies, or when
* there is very little free space anyway. (Besides, we start
* recording free space in the FSM once index vacuuming has been
* abandoned.)
*
* Note: The one-pass (no indexes) case is only supposed to make
* it this far when there were no LP_DEAD items during pruning.
*/
Assert(vacrel->nindexes > 0);
UnlockReleaseBuffer(buf);
}
else
if (vacrel->nindexes == 0
|| !vacrel->do_index_vacuuming
|| !prunestate.has_lpdead_items)
{
Size freespace = PageGetHeapFreeSpace(page);
UnlockReleaseBuffer(buf);
RecordPageWithFreeSpace(vacrel->rel, blkno, freespace);
/*
* Periodically perform FSM vacuuming to make newly-freed space
* visible on upper FSM pages. This is done after vacuuming if the
* table has indexes.
*/
if (vacrel->nindexes == 0 && prunestate.has_lpdead_items &&
blkno - next_fsm_block_to_vacuum >= VACUUM_FSM_EVERY_PAGES)
{
FreeSpaceMapVacuumRange(vacrel->rel, next_fsm_block_to_vacuum,
blkno);
next_fsm_block_to_vacuum = blkno;
}
}
else
UnlockReleaseBuffer(buf);
}
vacrel->blkno = InvalidBlockNumber;
@ -1596,8 +1540,13 @@ lazy_scan_prune(LVRelState *vacrel,
* in presult.ndeleted. It should not be confused with lpdead_items;
* lpdead_items's final value can be thought of as the number of tuples
* that were deleted from indexes.
*
* If the relation has no indexes, we can immediately mark would-be dead
* items LP_UNUSED, so mark_unused_now should be true if no indexes and
* false otherwise.
*/
heap_page_prune(rel, buf, vacrel->vistest, &presult, &vacrel->offnum);
heap_page_prune(rel, buf, vacrel->vistest, vacrel->nindexes == 0,
&presult, &vacrel->offnum);
/*
* Now scan the page to collect LP_DEAD items and check for tuples
@ -2520,7 +2469,7 @@ lazy_vacuum_heap_page(LVRelState *vacrel, BlockNumber blkno, Buffer buffer,
bool all_frozen;
LVSavedErrInfo saved_err_info;
Assert(vacrel->nindexes == 0 || vacrel->do_index_vacuuming);
Assert(vacrel->do_index_vacuuming);
pgstat_progress_update_param(PROGRESS_VACUUM_HEAP_BLKS_VACUUMED, blkno);