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Avoid creation of the free space map for small heap relations, take 2.

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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, 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
2019-02-04 07:49:15 +05:30
parent be12aa47e6
commit b0eaa4c51b
16 changed files with 543 additions and 102 deletions
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2
src/backend/access/brin/brin.c
View File

@@ -1150,7 +1150,7 @@ terminate_brin_buildstate(BrinBuildState *state)
freespace = PageGetFreeSpace(page);
blk = BufferGetBlockNumber(state->bs_currentInsertBuf);
ReleaseBuffer(state->bs_currentInsertBuf);
RecordPageWithFreeSpace(state->bs_irel, blk, freespace);
RecordPageWithFreeSpace(state->bs_irel, blk, freespace, InvalidBlockNumber);
FreeSpaceMapVacuumRange(state->bs_irel, blk, blk + 1);
}

10
src/backend/access/brin/brin_pageops.c
View File

@@ -310,7 +310,7 @@ brin_doupdate(Relation idxrel, BlockNumber pagesPerRange,
if (extended)
{
RecordPageWithFreeSpace(idxrel, newblk, freespace);
RecordPageWithFreeSpace(idxrel, newblk, freespace, InvalidBlockNumber);
FreeSpaceMapVacuumRange(idxrel, newblk, newblk + 1);
}
@@ -461,7 +461,7 @@ brin_doinsert(Relation idxrel, BlockNumber pagesPerRange,
if (extended)
{
RecordPageWithFreeSpace(idxrel, blk, freespace);
RecordPageWithFreeSpace(idxrel, blk, freespace, InvalidBlockNumber);
FreeSpaceMapVacuumRange(idxrel, blk, blk + 1);
}
@@ -654,7 +654,7 @@ brin_page_cleanup(Relation idxrel, Buffer buf)
/* Measure free space and record it */
RecordPageWithFreeSpace(idxrel, BufferGetBlockNumber(buf),
br_page_get_freespace(page));
br_page_get_freespace(page), InvalidBlockNumber);
}
/*
@@ -703,7 +703,7 @@ brin_getinsertbuffer(Relation irel, Buffer oldbuf, Size itemsz,
/* Choose initial target page, re-using existing target if known */
newblk = RelationGetTargetBlock(irel);
if (newblk == InvalidBlockNumber)
newblk = GetPageWithFreeSpace(irel, itemsz);
newblk = GetPageWithFreeSpace(irel, itemsz, true);
/*
* Loop until we find a page with sufficient free space. By the time we
@@ -895,7 +895,7 @@ brin_initialize_empty_new_buffer(Relation idxrel, Buffer buffer)
* pages whose FSM records were forgotten in a crash.
*/
RecordPageWithFreeSpace(idxrel, BufferGetBlockNumber(buffer),
br_page_get_freespace(page));
br_page_get_freespace(page), InvalidBlockNumber);
}