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Commitfaeedbc

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Introduce PG_IO_ALIGN_SIZE and align all I/O buffers.
In order to have the option to use O_DIRECT/FILE_FLAG_NO_BUFFERING in alater commit, we need the addresses of user space buffers to be wellaligned. The exact requirements vary by OS and file system (typicallysectors and/or memory pages). The address alignment size is set to4096, which is enough for currently known systems: it matches modernsectors and common memory page size. There is no standard governingO_DIRECT's requirements so we might eventually have to reconsider thiswith more information from the field or future systems.Aligning I/O buffers on memory pages is also known to improve regularbuffered I/O performance.Three classes of I/O buffers for regular data pages are adjusted:(1) Heap buffers are now allocated with the new palloc_aligned() orMemoryContextAllocAligned() functions introduced by commit439f617.(2) Stack buffers now use a new struct PGIOAlignedBlock to respectPG_IO_ALIGN_SIZE, if possible with this compiler. (3) The bufferpool is also aligned in shared memory.WAL buffers were already aligned on XLOG_BLCKSZ. It's possible forXLOG_BLCKSZ to be configured smaller than PG_IO_ALIGNED_SIZE and thusfor O_DIRECT WAL writes to fail to be well aligned, but that's apre-existing condition and will be addressed by a later commit.BufFiles are not yet addressed (there's no current plan to use O_DIRECTfor those, but they could potentially get some incidental speedup evenin plain buffered I/O operations through better alignment).If we can't align stack objects suitably using the compiler extensionswe know about, we disable the use of O_DIRECT by setting PG_O_DIRECT to0. This avoids the need to consider systems that have O_DIRECT butcan't align stack objects the way we want; such systems could in theorybe supported with more work but we don't currently know of any suchmachines, so it's easier to pretend there is no O_DIRECT supportinstead. That's an existing and tested class of system.Add assertions that all buffers passed into smgrread(), smgrwrite() andsmgrextend() are correctly aligned, unless PG_O_DIRECT is 0 (= stackalignment tricks may be unavailable) or the block size has been set toosmall to allow arrays of buffers to be all aligned.Author: Thomas Munro <thomas.munro@gmail.com>Author: Andres Freund <andres@anarazel.de>Reviewed-by: Justin Pryzby <pryzby@telsasoft.com>Discussion:https://postgr.es/m/CA+hUKGK1X532hYqJ_MzFWt0n1zt8trz980D79WbjwnT-yYLZpg@mail.gmail.com
1 parentd73c285 commitfaeedbc

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26 files changed

+108
-45
lines changed

26 files changed

+108
-45
lines changed

‎contrib/bloom/blinsert.c

Lines changed: 1 addition & 1 deletion
Original file line numberDiff line numberDiff line change
@@ -166,7 +166,7 @@ blbuildempty(Relation index)
166166
Pagemetapage;
167167

168168
/* Construct metapage. */
169-
metapage= (Page)palloc(BLCKSZ);
169+
metapage= (Page)palloc_aligned(BLCKSZ,PG_IO_ALIGN_SIZE,0);
170170
BloomFillMetapage(index,metapage);
171171

172172
/*

‎contrib/pg_prewarm/pg_prewarm.c

Lines changed: 1 addition & 1 deletion
Original file line numberDiff line numberDiff line change
@@ -36,7 +36,7 @@ typedef enum
3636
PREWARM_BUFFER
3737
}PrewarmType;
3838

39-
staticPGAlignedBlockblockbuffer;
39+
staticPGIOAlignedBlockblockbuffer;
4040

4141
/*
4242
* pg_prewarm(regclass, mode text, fork text,

‎src/backend/access/gist/gistbuild.c

Lines changed: 5 additions & 4 deletions
Original file line numberDiff line numberDiff line change
@@ -415,7 +415,7 @@ gist_indexsortbuild(GISTBuildState *state)
415415
* Write an empty page as a placeholder for the root page. It will be
416416
* replaced with the real root page at the end.
417417
*/
418-
page=palloc0(BLCKSZ);
418+
page=palloc_aligned(BLCKSZ,PG_IO_ALIGN_SIZE,MCXT_ALLOC_ZERO);
419419
smgrextend(RelationGetSmgr(state->indexrel),MAIN_FORKNUM,GIST_ROOT_BLKNO,
420420
page, true);
421421
state->pages_allocated++;
@@ -509,7 +509,8 @@ gist_indexsortbuild_levelstate_add(GISTBuildState *state,
509509
levelstate->current_page++;
510510

511511
if (levelstate->pages[levelstate->current_page]==NULL)
512-
levelstate->pages[levelstate->current_page]=palloc(BLCKSZ);
512+
levelstate->pages[levelstate->current_page]=
513+
palloc_aligned(BLCKSZ,PG_IO_ALIGN_SIZE,0);
513514

514515
newPage=levelstate->pages[levelstate->current_page];
515516
gistinitpage(newPage,old_page_flags);
@@ -579,7 +580,7 @@ gist_indexsortbuild_levelstate_flush(GISTBuildState *state,
579580

580581
/* Create page and copy data */
581582
data= (char*) (dist->list);
582-
target=palloc0(BLCKSZ);
583+
target=palloc_aligned(BLCKSZ,PG_IO_ALIGN_SIZE,MCXT_ALLOC_ZERO);
583584
gistinitpage(target,isleaf ?F_LEAF :0);
584585
for (inti=0;i<dist->block.num;i++)
585586
{
@@ -630,7 +631,7 @@ gist_indexsortbuild_levelstate_flush(GISTBuildState *state,
630631
if (parent==NULL)
631632
{
632633
parent=palloc0(sizeof(GistSortedBuildLevelState));
633-
parent->pages[0]= (Page)palloc(BLCKSZ);
634+
parent->pages[0]= (Page)palloc_aligned(BLCKSZ,PG_IO_ALIGN_SIZE,0);
634635
parent->parent=NULL;
635636
gistinitpage(parent->pages[0],0);
636637

‎src/backend/access/hash/hashpage.c

Lines changed: 1 addition & 1 deletion
Original file line numberDiff line numberDiff line change
@@ -992,7 +992,7 @@ static bool
992992
_hash_alloc_buckets(Relationrel,BlockNumberfirstblock,uint32nblocks)
993993
{
994994
BlockNumberlastblock;
995-
PGAlignedBlockzerobuf;
995+
PGIOAlignedBlockzerobuf;
996996
Pagepage;
997997
HashPageOpaqueovflopaque;
998998

‎src/backend/access/heap/rewriteheap.c

Lines changed: 1 addition & 1 deletion
Original file line numberDiff line numberDiff line change
@@ -255,7 +255,7 @@ begin_heap_rewrite(Relation old_heap, Relation new_heap, TransactionId oldest_xm
255255

256256
state->rs_old_rel=old_heap;
257257
state->rs_new_rel=new_heap;
258-
state->rs_buffer= (Page)palloc(BLCKSZ);
258+
state->rs_buffer= (Page)palloc_aligned(BLCKSZ,PG_IO_ALIGN_SIZE,0);
259259
/* new_heap needn't be empty, just locked */
260260
state->rs_blockno=RelationGetNumberOfBlocks(new_heap);
261261
state->rs_buffer_valid= false;

‎src/backend/access/nbtree/nbtree.c

Lines changed: 1 addition & 1 deletion
Original file line numberDiff line numberDiff line change
@@ -154,7 +154,7 @@ btbuildempty(Relation index)
154154
Pagemetapage;
155155

156156
/* Construct metapage. */
157-
metapage= (Page)palloc(BLCKSZ);
157+
metapage= (Page)palloc_aligned(BLCKSZ,PG_IO_ALIGN_SIZE,0);
158158
_bt_initmetapage(metapage,P_NONE,0,_bt_allequalimage(index, false));
159159

160160
/*

‎src/backend/access/nbtree/nbtsort.c

Lines changed: 5 additions & 3 deletions
Original file line numberDiff line numberDiff line change
@@ -619,7 +619,7 @@ _bt_blnewpage(uint32 level)
619619
Pagepage;
620620
BTPageOpaqueopaque;
621621

622-
page= (Page)palloc(BLCKSZ);
622+
page= (Page)palloc_aligned(BLCKSZ,PG_IO_ALIGN_SIZE,0);
623623

624624
/* Zero the page and set up standard page header info */
625625
_bt_pageinit(page,BLCKSZ);
@@ -660,7 +660,9 @@ _bt_blwritepage(BTWriteState *wstate, Page page, BlockNumber blkno)
660660
while (blkno>wstate->btws_pages_written)
661661
{
662662
if (!wstate->btws_zeropage)
663-
wstate->btws_zeropage= (Page)palloc0(BLCKSZ);
663+
wstate->btws_zeropage= (Page)palloc_aligned(BLCKSZ,
664+
PG_IO_ALIGN_SIZE,
665+
MCXT_ALLOC_ZERO);
664666
/* don't set checksum for all-zero page */
665667
smgrextend(RelationGetSmgr(wstate->index),MAIN_FORKNUM,
666668
wstate->btws_pages_written++,
@@ -1170,7 +1172,7 @@ _bt_uppershutdown(BTWriteState *wstate, BTPageState *state)
11701172
* set to point to "P_NONE"). This changes the index to the "valid" state
11711173
* by filling in a valid magic number in the metapage.
11721174
*/
1173-
metapage= (Page)palloc(BLCKSZ);
1175+
metapage= (Page)palloc_aligned(BLCKSZ,PG_IO_ALIGN_SIZE,0);
11741176
_bt_initmetapage(metapage,rootblkno,rootlevel,
11751177
wstate->inskey->allequalimage);
11761178
_bt_blwritepage(wstate,metapage,BTREE_METAPAGE);

‎src/backend/access/spgist/spginsert.c

Lines changed: 1 addition & 1 deletion
Original file line numberDiff line numberDiff line change
@@ -158,7 +158,7 @@ spgbuildempty(Relation index)
158158
Pagepage;
159159

160160
/* Construct metapage. */
161-
page= (Page)palloc(BLCKSZ);
161+
page= (Page)palloc_aligned(BLCKSZ,PG_IO_ALIGN_SIZE,0);
162162
SpGistInitMetapage(page);
163163

164164
/*

‎src/backend/access/transam/generic_xlog.c

Lines changed: 9 additions & 4 deletions
Original file line numberDiff line numberDiff line change
@@ -58,14 +58,17 @@ typedef struct
5858
chardelta[MAX_DELTA_SIZE];/* delta between page images */
5959
}PageData;
6060

61-
/* State of generic xlog record construction */
61+
/*
62+
* State of generic xlog record construction. Must be allocated at an I/O
63+
* aligned address.
64+
*/
6265
structGenericXLogState
6366
{
67+
/* Page images (properly aligned, must be first) */
68+
PGIOAlignedBlockimages[MAX_GENERIC_XLOG_PAGES];
6469
/* Info about each page, see above */
6570
PageDatapages[MAX_GENERIC_XLOG_PAGES];
6671
boolisLogged;
67-
/* Page images (properly aligned) */
68-
PGAlignedBlockimages[MAX_GENERIC_XLOG_PAGES];
6972
};
7073

7174
staticvoidwriteFragment(PageData*pageData,OffsetNumberoffset,
@@ -269,7 +272,9 @@ GenericXLogStart(Relation relation)
269272
GenericXLogState*state;
270273
inti;
271274

272-
state= (GenericXLogState*)palloc(sizeof(GenericXLogState));
275+
state= (GenericXLogState*)palloc_aligned(sizeof(GenericXLogState),
276+
PG_IO_ALIGN_SIZE,
277+
0);
273278
state->isLogged=RelationNeedsWAL(relation);
274279

275280
for (i=0;i<MAX_GENERIC_XLOG_PAGES;i++)

‎src/backend/access/transam/xlog.c

Lines changed: 1 addition & 1 deletion
Original file line numberDiff line numberDiff line change
@@ -4506,7 +4506,7 @@ XLOGShmemSize(void)
45064506
/* xlblocks array */
45074507
size=add_size(size,mul_size(sizeof(XLogRecPtr),XLOGbuffers));
45084508
/* extra alignment padding for XLOG I/O buffers */
4509-
size=add_size(size,XLOG_BLCKSZ);
4509+
size=add_size(size,Max(XLOG_BLCKSZ,PG_IO_ALIGN_SIZE));
45104510
/* and the buffers themselves */
45114511
size=add_size(size,mul_size(XLOG_BLCKSZ,XLOGbuffers));
45124512

‎src/backend/catalog/storage.c

Lines changed: 1 addition & 1 deletion
Original file line numberDiff line numberDiff line change
@@ -451,7 +451,7 @@ void
451451
RelationCopyStorage(SMgrRelationsrc,SMgrRelationdst,
452452
ForkNumberforkNum,charrelpersistence)
453453
{
454-
PGAlignedBlockbuf;
454+
PGIOAlignedBlockbuf;
455455
Pagepage;
456456
booluse_wal;
457457
boolcopying_initfork;

‎src/backend/storage/buffer/buf_init.c

Lines changed: 7 additions & 3 deletions
Original file line numberDiff line numberDiff line change
@@ -78,9 +78,12 @@ InitBufferPool(void)
7878
NBuffers*sizeof(BufferDescPadded),
7979
&foundDescs);
8080

81+
/* Align buffer pool on IO page size boundary. */
8182
BufferBlocks= (char*)
82-
ShmemInitStruct("Buffer Blocks",
83-
NBuffers* (Size)BLCKSZ,&foundBufs);
83+
TYPEALIGN(PG_IO_ALIGN_SIZE,
84+
ShmemInitStruct("Buffer Blocks",
85+
NBuffers* (Size)BLCKSZ+PG_IO_ALIGN_SIZE,
86+
&foundBufs));
8487

8588
/* Align condition variables to cacheline boundary. */
8689
BufferIOCVArray= (ConditionVariableMinimallyPadded*)
@@ -163,7 +166,8 @@ BufferShmemSize(void)
163166
/* to allow aligning buffer descriptors */
164167
size=add_size(size,PG_CACHE_LINE_SIZE);
165168

166-
/* size of data pages */
169+
/* size of data pages, plus alignment padding */
170+
size=add_size(size,PG_IO_ALIGN_SIZE);
167171
size=add_size(size,mul_size(NBuffers,BLCKSZ));
168172

169173
/* size of stuff controlled by freelist.c */

‎src/backend/storage/buffer/bufmgr.c

Lines changed: 1 addition & 1 deletion
Original file line numberDiff line numberDiff line change
@@ -4250,7 +4250,7 @@ RelationCopyStorageUsingBuffer(RelFileLocator srclocator,
42504250
booluse_wal;
42514251
BlockNumbernblocks;
42524252
BlockNumberblkno;
4253-
PGAlignedBlockbuf;
4253+
PGIOAlignedBlockbuf;
42544254
BufferAccessStrategybstrategy_src;
42554255
BufferAccessStrategybstrategy_dst;
42564256

‎src/backend/storage/buffer/localbuf.c

Lines changed: 5 additions & 2 deletions
Original file line numberDiff line numberDiff line change
@@ -744,8 +744,11 @@ GetLocalBufferStorage(void)
744744
/* And don't overflow MaxAllocSize, either */
745745
num_bufs=Min(num_bufs,MaxAllocSize /BLCKSZ);
746746

747-
cur_block= (char*)MemoryContextAlloc(LocalBufferContext,
748-
num_bufs*BLCKSZ);
747+
/* Buffers should be I/O aligned. */
748+
cur_block= (char*)
749+
TYPEALIGN(PG_IO_ALIGN_SIZE,
750+
MemoryContextAlloc(LocalBufferContext,
751+
num_bufs*BLCKSZ+PG_IO_ALIGN_SIZE));
749752
next_buf_in_block=0;
750753
num_bufs_in_block=num_bufs;
751754
}

‎src/backend/storage/file/buffile.c

Lines changed: 6 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -95,6 +95,12 @@ struct BufFile
9595
off_tcurOffset;/* offset part of current pos */
9696
intpos;/* next read/write position in buffer */
9797
intnbytes;/* total # of valid bytes in buffer */
98+
99+
/*
100+
* XXX Should ideally us PGIOAlignedBlock, but might need a way to avoid
101+
* wasting per-file alignment padding when some users create many
102+
* files.
103+
*/
98104
PGAlignedBlockbuffer;
99105
};
100106

‎src/backend/storage/page/bufpage.c

Lines changed: 4 additions & 1 deletion
Original file line numberDiff line numberDiff line change
@@ -1522,7 +1522,10 @@ PageSetChecksumCopy(Page page, BlockNumber blkno)
15221522
* and second to avoid wasting space in processes that never call this.
15231523
*/
15241524
if (pageCopy==NULL)
1525-
pageCopy=MemoryContextAlloc(TopMemoryContext,BLCKSZ);
1525+
pageCopy=MemoryContextAllocAligned(TopMemoryContext,
1526+
BLCKSZ,
1527+
PG_IO_ALIGN_SIZE,
1528+
0);
15261529

15271530
memcpy(pageCopy, (char*)page,BLCKSZ);
15281531
((PageHeader)pageCopy)->pd_checksum=pg_checksum_page(pageCopy,blkno);

‎src/backend/storage/smgr/md.c

Lines changed: 14 additions & 1 deletion
Original file line numberDiff line numberDiff line change
@@ -453,6 +453,10 @@ mdextend(SMgrRelation reln, ForkNumber forknum, BlockNumber blocknum,
453453
intnbytes;
454454
MdfdVec*v;
455455

456+
/* If this build supports direct I/O, the buffer must be I/O aligned. */
457+
if (PG_O_DIRECT!=0&&PG_IO_ALIGN_SIZE <=BLCKSZ)
458+
Assert((uintptr_t)buffer==TYPEALIGN(PG_IO_ALIGN_SIZE,buffer));
459+
456460
/* This assert is too expensive to have on normally ... */
457461
#ifdefCHECK_WRITE_VS_EXTEND
458462
Assert(blocknum >=mdnblocks(reln,forknum));
@@ -783,6 +787,10 @@ mdread(SMgrRelation reln, ForkNumber forknum, BlockNumber blocknum,
783787
intnbytes;
784788
MdfdVec*v;
785789

790+
/* If this build supports direct I/O, the buffer must be I/O aligned. */
791+
if (PG_O_DIRECT!=0&&PG_IO_ALIGN_SIZE <=BLCKSZ)
792+
Assert((uintptr_t)buffer==TYPEALIGN(PG_IO_ALIGN_SIZE,buffer));
793+
786794
TRACE_POSTGRESQL_SMGR_MD_READ_START(forknum,blocknum,
787795
reln->smgr_rlocator.locator.spcOid,
788796
reln->smgr_rlocator.locator.dbOid,
@@ -848,6 +856,10 @@ mdwrite(SMgrRelation reln, ForkNumber forknum, BlockNumber blocknum,
848856
intnbytes;
849857
MdfdVec*v;
850858

859+
/* If this build supports direct I/O, the buffer must be I/O aligned. */
860+
if (PG_O_DIRECT!=0&&PG_IO_ALIGN_SIZE <=BLCKSZ)
861+
Assert((uintptr_t)buffer==TYPEALIGN(PG_IO_ALIGN_SIZE,buffer));
862+
851863
/* This assert is too expensive to have on normally ... */
852864
#ifdefCHECK_WRITE_VS_EXTEND
853865
Assert(blocknum<mdnblocks(reln,forknum));
@@ -1429,7 +1441,8 @@ _mdfd_getseg(SMgrRelation reln, ForkNumber forknum, BlockNumber blkno,
14291441
*/
14301442
if (nblocks< ((BlockNumber)RELSEG_SIZE))
14311443
{
1432-
char*zerobuf=palloc0(BLCKSZ);
1444+
char*zerobuf=palloc_aligned(BLCKSZ,PG_IO_ALIGN_SIZE,
1445+
MCXT_ALLOC_ZERO);
14331446

14341447
mdextend(reln,forknum,
14351448
nextsegno* ((BlockNumber)RELSEG_SIZE)-1,

‎src/backend/utils/sort/logtape.c

Lines changed: 1 addition & 1 deletion
Original file line numberDiff line numberDiff line change
@@ -252,7 +252,7 @@ ltsWriteBlock(LogicalTapeSet *lts, long blocknum, const void *buffer)
252252
*/
253253
while (blocknum>lts->nBlocksWritten)
254254
{
255-
PGAlignedBlockzerobuf;
255+
PGIOAlignedBlockzerobuf;
256256

257257
MemSet(zerobuf.data,0,sizeof(zerobuf));
258258

‎src/bin/pg_checksums/pg_checksums.c

Lines changed: 1 addition & 1 deletion
Original file line numberDiff line numberDiff line change
@@ -183,7 +183,7 @@ skipfile(const char *fn)
183183
staticvoid
184184
scan_file(constchar*fn,intsegmentno)
185185
{
186-
PGAlignedBlockbuf;
186+
PGIOAlignedBlockbuf;
187187
PageHeaderheader= (PageHeader)buf.data;
188188
intf;
189189
BlockNumberblockno;

‎src/bin/pg_rewind/local_source.c

Lines changed: 2 additions & 2 deletions
Original file line numberDiff line numberDiff line change
@@ -77,7 +77,7 @@ static void
7777
local_queue_fetch_file(rewind_source*source,constchar*path,size_tlen)
7878
{
7979
constchar*datadir= ((local_source*)source)->datadir;
80-
PGAlignedBlockbuf;
80+
PGIOAlignedBlockbuf;
8181
charsrcpath[MAXPGPATH];
8282
intsrcfd;
8383
size_twritten_len;
@@ -129,7 +129,7 @@ local_queue_fetch_range(rewind_source *source, const char *path, off_t off,
129129
size_tlen)
130130
{
131131
constchar*datadir= ((local_source*)source)->datadir;
132-
PGAlignedBlockbuf;
132+
PGIOAlignedBlockbuf;
133133
charsrcpath[MAXPGPATH];
134134
intsrcfd;
135135
off_tbegin=off;

‎src/bin/pg_upgrade/file.c

Lines changed: 2 additions & 2 deletions
Original file line numberDiff line numberDiff line change
@@ -178,8 +178,8 @@ rewriteVisibilityMap(const char *fromfile, const char *tofile,
178178
{
179179
intsrc_fd;
180180
intdst_fd;
181-
PGAlignedBlockbuffer;
182-
PGAlignedBlocknew_vmbuf;
181+
PGIOAlignedBlockbuffer;
182+
PGIOAlignedBlocknew_vmbuf;
183183
ssize_ttotalBytesRead=0;
184184
ssize_tsrc_filesize;
185185
intrewriteVmBytesPerPage;

‎src/common/file_utils.c

Lines changed: 2 additions & 2 deletions
Original file line numberDiff line numberDiff line change
@@ -540,8 +540,8 @@ pg_pwritev_with_retry(int fd, const struct iovec *iov, int iovcnt, off_t offset)
540540
ssize_t
541541
pg_pwrite_zeros(intfd,size_tsize,off_toffset)
542542
{
543-
staticconstPGAlignedBlockzbuffer= {{0}};/* worth BLCKSZ */
544-
void*zerobuf_addr=unconstify(PGAlignedBlock*,&zbuffer)->data;
543+
staticconstPGIOAlignedBlockzbuffer= {{0}};/* worth BLCKSZ */
544+
void*zerobuf_addr=unconstify(PGIOAlignedBlock*,&zbuffer)->data;
545545
structioveciov[PG_IOV_MAX];
546546
size_tremaining_size=size;
547547
ssize_ttotal_written=0;

‎src/include/c.h

Lines changed: 26 additions & 8 deletions
Original file line numberDiff line numberDiff line change
@@ -1119,14 +1119,11 @@ extern void ExceptionalCondition(const char *conditionName,
11191119

11201120
/*
11211121
* Use this, not "char buf[BLCKSZ]", to declare a field or local variable
1122-
* holding a page buffer, if that page might be accessed as a page and not
1123-
* just a string of bytes. Otherwise the variable might be under-aligned,
1124-
* causing problems on alignment-picky hardware. (In some places, we use
1125-
* this to declare buffers even though we only pass them to read() and
1126-
* write(), because copying to/from aligned buffers is usually faster than
1127-
* using unaligned buffers.) We include both "double" and "int64" in the
1128-
* union to ensure that the compiler knows the value must be MAXALIGN'ed
1129-
* (cf. configure's computation of MAXIMUM_ALIGNOF).
1122+
* holding a page buffer, if that page might be accessed as a page. Otherwise
1123+
* the variable might be under-aligned, causing problems on alignment-picky
1124+
* hardware. We include both "double" and "int64" in the union to ensure that
1125+
* the compiler knows the value must be MAXALIGN'ed (cf. configure's
1126+
* computation of MAXIMUM_ALIGNOF).
11301127
*/
11311128
typedefunionPGAlignedBlock
11321129
{
@@ -1135,9 +1132,30 @@ typedef union PGAlignedBlock
11351132
int64force_align_i64;
11361133
}PGAlignedBlock;
11371134

1135+
/*
1136+
* Use this to declare a field or local variable holding a page buffer, if that
1137+
* page might be accessed as a page or passed to an SMgr I/O function. If
1138+
* allocating using the MemoryContext API, the aligned allocation functions
1139+
* should be used with PG_IO_ALIGN_SIZE. This alignment may be more efficient
1140+
* for I/O in general, but may be strictly required on some platforms when
1141+
* using direct I/O.
1142+
*/
1143+
typedefunionPGIOAlignedBlock
1144+
{
1145+
#ifdefpg_attribute_aligned
1146+
pg_attribute_aligned(PG_IO_ALIGN_SIZE)
1147+
#endif
1148+
chardata[BLCKSZ];
1149+
doubleforce_align_d;
1150+
int64force_align_i64;
1151+
}PGIOAlignedBlock;
1152+
11381153
/* Same, but for an XLOG_BLCKSZ-sized buffer */
11391154
typedefunionPGAlignedXLogBlock
11401155
{
1156+
#ifdefpg_attribute_aligned
1157+
pg_attribute_aligned(PG_IO_ALIGN_SIZE)
1158+
#endif
11411159
chardata[XLOG_BLCKSZ];
11421160
doubleforce_align_d;
11431161
int64force_align_i64;

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