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Avoid creation of the free space map for small heap relations.

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Previously, all heaps had FSMs. For very small tables, this means that the
FSM took up more space than the heap did. This is wasteful, so now we
refrain from creating the FSM for heaps with 4 pages or fewer. If the last
known target block has insufficient space, we still try to insert into some
other page before giving up and extending the relation, since doing
otherwise leads to table bloat. Testing showed that trying every page
penalized performance slightly, so we compromise and try every other page.
This way, we visit at most two pages. Any pages with wasted free space
become visible at next relation extension, so we still control table bloat.
As a bonus, directly attempting one or two pages can even be faster than
consulting the FSM would have been.

Once the FSM is created for a heap we don't remove it even if somebody
deletes all the rows from the corresponding relation.  We don't think it is
a useful optimization as it is quite likely that relation will again grow
to the same size.

Author: John Naylor with design inputs and some code contribution by Amit Kapila
Reviewed-by: Amit Kapila
Tested-by: Mithun C Y
Discussion: https://www.postgresql.org/message-id/CAJVSVGWvB13PzpbLEecFuGFc5V2fsO736BsdTakPiPAcdMM5tQ@mail.gmail.com
This commit is contained in:
Amit Kapila
2019-01-28 08:14:06 +05:30
parent d66e3664b8
commit ac88d2962a
16 changed files with 576 additions and 102 deletions
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17
src/backend/access/heap/vacuumlazy.c
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@@ -153,7 +153,7 @@ static BufferAccessStrategy vac_strategy;
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 void lazy_vacuum_heap(Relation onerel, LVRelStats *vacrelstats, BlockNumber nblocks);
static bool lazy_check_needs_freeze(Buffer buf, bool *hastup);
static void lazy_vacuum_index(Relation indrel,
IndexBulkDeleteResult **stats,
@@ -758,7 +758,7 @@ lazy_scan_heap(Relation onerel, int options, LVRelStats *vacrelstats,
pgstat_progress_update_multi_param(2, hvp_index, hvp_val);
/* Remove tuples from heap */
lazy_vacuum_heap(onerel, vacrelstats);
lazy_vacuum_heap(onerel, vacrelstats, nblocks);
/*
* Forget the now-vacuumed tuples, and press on, but be careful
@@ -896,7 +896,7 @@ lazy_scan_heap(Relation onerel, int options, LVRelStats *vacrelstats,
MarkBufferDirty(buf);
UnlockReleaseBuffer(buf);
RecordPageWithFreeSpace(onerel, blkno, freespace);
RecordPageWithFreeSpace(onerel, blkno, freespace, nblocks);
continue;
}
@@ -935,7 +935,7 @@ lazy_scan_heap(Relation onerel, int options, LVRelStats *vacrelstats,
}
UnlockReleaseBuffer(buf);
RecordPageWithFreeSpace(onerel, blkno, freespace);
RecordPageWithFreeSpace(onerel, blkno, freespace, nblocks);
continue;
}
@@ -1332,7 +1332,7 @@ lazy_scan_heap(Relation onerel, int options, LVRelStats *vacrelstats,
* taken if there are no indexes.)
*/
if (vacrelstats->num_dead_tuples == prev_dead_count)
RecordPageWithFreeSpace(onerel, blkno, freespace);
RecordPageWithFreeSpace(onerel, blkno, freespace, nblocks);
}
/* report that everything is scanned and vacuumed */
@@ -1394,7 +1394,7 @@ lazy_scan_heap(Relation onerel, int options, LVRelStats *vacrelstats,
/* Remove tuples from heap */
pgstat_progress_update_param(PROGRESS_VACUUM_PHASE,
PROGRESS_VACUUM_PHASE_VACUUM_HEAP);
lazy_vacuum_heap(onerel, vacrelstats);
lazy_vacuum_heap(onerel, vacrelstats, nblocks);
vacrelstats->num_index_scans++;
}
@@ -1465,9 +1465,10 @@ lazy_scan_heap(Relation onerel, int options, LVRelStats *vacrelstats,
* Note: the reason for doing this as a second pass is we cannot remove
* the tuples until we've removed their index entries, and we want to
* process index entry removal in batches as large as possible.
* Note: nblocks is passed as an optimization for RecordPageWithFreeSpace().
*/
static void
lazy_vacuum_heap(Relation onerel, LVRelStats *vacrelstats)
lazy_vacuum_heap(Relation onerel, LVRelStats *vacrelstats, BlockNumber nblocks)
{
int tupindex;
int npages;
@@ -1504,7 +1505,7 @@ lazy_vacuum_heap(Relation onerel, LVRelStats *vacrelstats)
freespace = PageGetHeapFreeSpace(page);
UnlockReleaseBuffer(buf);
RecordPageWithFreeSpace(onerel, tblk, freespace);
RecordPageWithFreeSpace(onerel, tblk, freespace, nblocks);
npages++;
}