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Commit0ff8bbd

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Accept slightly-filled pages for tuples larger than fillfactor.
We always inserted a larger-than-fillfactor tuple into a newly-extendedpage, even when existing pages were empty or contained nothing but anunused line pointer. This was unnecessary relation extension. Starttolerating page usage up to 1/8 the maximum space that could be taken upby line pointers. This is somewhat arbitrary, but it should allow morecases to reuse pages. This has no effect on tables with fillfactor=100(the default).John Naylor and Floris van Nee. Reviewed by Matthias van de Meent.Reported by Floris van Nee.Discussion:https://postgr.es/m/6e263217180649339720afe2176c50aa@opammb0562.comp.optiver.com
1 parent7ef64e7 commit0ff8bbd

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4 files changed

+74
-18
lines changed

4 files changed

+74
-18
lines changed

‎src/backend/access/heap/hio.c

Lines changed: 26 additions & 17 deletions
Original file line numberDiff line numberDiff line change
@@ -317,10 +317,10 @@ RelationAddExtraBlocks(Relation relation, BulkInsertState bistate)
317317
*BULKWRITE buffer selection strategy object to the buffer manager.
318318
*Passing NULL for bistate selects the default behavior.
319319
*
320-
*Wealways try to avoid fillingexisting pages further than the fillfactor.
321-
*This is OK since this routine is not consulted when updating a tuple and
322-
*keeping it on the same page, which is the scenario fillfactor is meant
323-
*to reserve space for.
320+
*Wedon't fillexisting pages further than the fillfactor, except for large
321+
*tuples in nearly-empty pages.This is OK since this routine is not
322+
*consulted when updating a tuple andkeeping it on the same page, which is
323+
*the scenario fillfactor is meantto reserve space for.
324324
*
325325
*ereport(ERROR) is allowed here, so this routine *must* be called
326326
*before any (unlogged) changes are made in buffer pool.
@@ -334,8 +334,10 @@ RelationGetBufferForTuple(Relation relation, Size len,
334334
booluse_fsm= !(options&HEAP_INSERT_SKIP_FSM);
335335
Bufferbuffer=InvalidBuffer;
336336
Pagepage;
337-
SizepageFreeSpace=0,
338-
saveFreeSpace=0;
337+
SizenearlyEmptyFreeSpace,
338+
pageFreeSpace=0,
339+
saveFreeSpace=0,
340+
targetFreeSpace=0;
339341
BlockNumbertargetBlock,
340342
otherBlock;
341343
boolneedLock;
@@ -358,6 +360,19 @@ RelationGetBufferForTuple(Relation relation, Size len,
358360
saveFreeSpace=RelationGetTargetPageFreeSpace(relation,
359361
HEAP_DEFAULT_FILLFACTOR);
360362

363+
/*
364+
* Since pages without tuples can still have line pointers, we consider
365+
* pages "empty" when the unavailable space is slight. This threshold is
366+
* somewhat arbitrary, but it should prevent most unnecessary relation
367+
* extensions while inserting large tuples into low-fillfactor tables.
368+
*/
369+
nearlyEmptyFreeSpace=MaxHeapTupleSize-
370+
(MaxHeapTuplesPerPage /8*sizeof(ItemIdData));
371+
if (len+saveFreeSpace>nearlyEmptyFreeSpace)
372+
targetFreeSpace=Max(len,nearlyEmptyFreeSpace);
373+
else
374+
targetFreeSpace=len+saveFreeSpace;
375+
361376
if (otherBuffer!=InvalidBuffer)
362377
otherBlock=BufferGetBlockNumber(otherBuffer);
363378
else
@@ -376,13 +391,7 @@ RelationGetBufferForTuple(Relation relation, Size len,
376391
* When use_fsm is false, we either put the tuple onto the existing target
377392
* page or extend the relation.
378393
*/
379-
if (len+saveFreeSpace>MaxHeapTupleSize)
380-
{
381-
/* can't fit, don't bother asking FSM */
382-
targetBlock=InvalidBlockNumber;
383-
use_fsm= false;
384-
}
385-
elseif (bistate&&bistate->current_buf!=InvalidBuffer)
394+
if (bistate&&bistate->current_buf!=InvalidBuffer)
386395
targetBlock=BufferGetBlockNumber(bistate->current_buf);
387396
else
388397
targetBlock=RelationGetTargetBlock(relation);
@@ -393,7 +402,7 @@ RelationGetBufferForTuple(Relation relation, Size len,
393402
* We have no cached target page, so ask the FSM for an initial
394403
* target.
395404
*/
396-
targetBlock=GetPageWithFreeSpace(relation,len+saveFreeSpace);
405+
targetBlock=GetPageWithFreeSpace(relation,targetFreeSpace);
397406
}
398407

399408
/*
@@ -517,7 +526,7 @@ RelationGetBufferForTuple(Relation relation, Size len,
517526
}
518527

519528
pageFreeSpace=PageGetHeapFreeSpace(page);
520-
if (len+saveFreeSpace <=pageFreeSpace)
529+
if (targetFreeSpace <=pageFreeSpace)
521530
{
522531
/* use this page as future insert target, too */
523532
RelationSetTargetBlock(relation,targetBlock);
@@ -550,7 +559,7 @@ RelationGetBufferForTuple(Relation relation, Size len,
550559
targetBlock=RecordAndGetPageWithFreeSpace(relation,
551560
targetBlock,
552561
pageFreeSpace,
553-
len+saveFreeSpace);
562+
targetFreeSpace);
554563
}
555564

556565
/*
@@ -582,7 +591,7 @@ RelationGetBufferForTuple(Relation relation, Size len,
582591
* Check if some other backend has extended a block for us while
583592
* we were waiting on the lock.
584593
*/
585-
targetBlock=GetPageWithFreeSpace(relation,len+saveFreeSpace);
594+
targetBlock=GetPageWithFreeSpace(relation,targetFreeSpace);
586595

587596
/*
588597
* If some other waiter has already extended the relation, we

‎src/backend/access/heap/rewriteheap.c

Lines changed: 5 additions & 1 deletion
Original file line numberDiff line numberDiff line change
@@ -676,7 +676,11 @@ raw_heap_insert(RewriteState state, HeapTuple tup)
676676

677677
if (len+saveFreeSpace>pageFreeSpace)
678678
{
679-
/* Doesn't fit, so write out the existing page */
679+
/*
680+
* Doesn't fit, so write out the existing page. It always
681+
* contains a tuple. Hence, unlike RelationGetBufferForTuple(),
682+
* enforce saveFreeSpace unconditionally.
683+
*/
680684

681685
/* XLOG stuff */
682686
if (RelationNeedsWAL(state->rs_new_rel))

‎src/test/regress/expected/insert.out

Lines changed: 21 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -82,6 +82,27 @@ select col1, col2, char_length(col3) from inserttest;
8282

8383
drop table inserttest;
8484
--
85+
-- tuple larger than fillfactor
86+
--
87+
CREATE TABLE large_tuple_test (a int, b text) WITH (fillfactor = 10);
88+
ALTER TABLE large_tuple_test ALTER COLUMN b SET STORAGE plain;
89+
-- create page w/ free space in range [nearlyEmptyFreeSpace, MaxHeapTupleSize)
90+
INSERT INTO large_tuple_test (select 1, NULL);
91+
-- should still fit on the page
92+
INSERT INTO large_tuple_test (select 2, repeat('a', 1000));
93+
SELECT pg_size_pretty(pg_relation_size('large_tuple_test'::regclass, 'main'));
94+
pg_size_pretty
95+
----------------
96+
8192 bytes
97+
(1 row)
98+
99+
-- add small record to the second page
100+
INSERT INTO large_tuple_test (select 3, NULL);
101+
-- now this tuple won't fit on the second page, but the insert should
102+
-- still succeed by extending the relation
103+
INSERT INTO large_tuple_test (select 4, repeat('a', 8126));
104+
DROP TABLE large_tuple_test;
105+
--
85106
-- check indirection (field/array assignment), cf bug #14265
86107
--
87108
-- these tests are aware that transformInsertStmt has 3 separate code paths

‎src/test/regress/sql/insert.sql

Lines changed: 22 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -37,6 +37,28 @@ select col1, col2, char_length(col3) from inserttest;
3737

3838
droptable inserttest;
3939

40+
--
41+
-- tuple larger than fillfactor
42+
--
43+
CREATETABLElarge_tuple_test (aint, btext) WITH (fillfactor=10);
44+
ALTERTABLE large_tuple_test ALTER COLUMN bSET STORAGE plain;
45+
46+
-- create page w/ free space in range [nearlyEmptyFreeSpace, MaxHeapTupleSize)
47+
INSERT INTO large_tuple_test (select1,NULL);
48+
49+
-- should still fit on the page
50+
INSERT INTO large_tuple_test (select2, repeat('a',1000));
51+
SELECT pg_size_pretty(pg_relation_size('large_tuple_test'::regclass,'main'));
52+
53+
-- add small record to the second page
54+
INSERT INTO large_tuple_test (select3,NULL);
55+
56+
-- now this tuple won't fit on the second page, but the insert should
57+
-- still succeed by extending the relation
58+
INSERT INTO large_tuple_test (select4, repeat('a',8126));
59+
60+
DROPTABLE large_tuple_test;
61+
4062
--
4163
-- check indirection (field/array assignment), cf bug #14265
4264
--

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