]> git.ipfire.org Git - thirdparty/postgresql.git/commitdiff
Avoid using potentially-under-aligned page buffers.
authorTom Lane <tgl@sss.pgh.pa.us>
Sat, 1 Sep 2018 19:27:13 +0000 (15:27 -0400)
committerTom Lane <tgl@sss.pgh.pa.us>
Sat, 1 Sep 2018 19:27:13 +0000 (15:27 -0400)
There's a project policy against using plain "char buf[BLCKSZ]" local
or static variables as page buffers; preferred style is to palloc or
malloc each buffer to ensure it is MAXALIGN'd.  However, that policy's
been ignored in an increasing number of places.  We've apparently got
away with it so far, probably because (a) relatively few people use
platforms on which misalignment causes core dumps and/or (b) the
variables chance to be sufficiently aligned anyway.  But this is not
something to rely on.  Moreover, even if we don't get a core dump,
we might be paying a lot of cycles for misaligned accesses.

To fix, invent new union types PGAlignedBlock and PGAlignedXLogBlock
that the compiler must allocate with sufficient alignment, and use
those in place of plain char arrays.

I used these types even for variables where there's no risk of a
misaligned access, since ensuring proper alignment should make
kernel data transfers faster.  I also changed some places where
we had been palloc'ing short-lived buffers, for coding style
uniformity and to save palloc/pfree overhead.

Since this seems to be a live portability hazard (despite the lack
of field reports), back-patch to all supported versions.

Patch by me; thanks to Michael Paquier for review.

Discussion: https://postgr.es/m/1535618100.1286.3.camel@credativ.de

21 files changed:
contrib/bloom/blinsert.c
contrib/pg_prewarm/pg_prewarm.c
src/backend/access/gin/ginentrypage.c
src/backend/access/gin/ginfast.c
src/backend/access/hash/hashpage.c
src/backend/access/heap/heapam.c
src/backend/access/heap/visibilitymap.c
src/backend/access/transam/generic_xlog.c
src/backend/access/transam/xlog.c
src/backend/access/transam/xloginsert.c
src/backend/access/transam/xlogreader.c
src/backend/commands/tablecmds.c
src/backend/replication/walsender.c
src/backend/storage/file/buffile.c
src/backend/storage/freespace/freespace.c
src/backend/utils/sort/logtape.c
src/bin/pg_basebackup/walmethods.c
src/bin/pg_resetwal/pg_resetwal.c
src/bin/pg_rewind/copy_fetch.c
src/bin/pg_upgrade/file.c
src/include/c.h

index 28c6c0ba6fc783419f699ed7923673aa3aca8b75..0039c4785fecbb37c259237c88bacb7b41065f14 100644 (file)
@@ -36,7 +36,7 @@ typedef struct
        int64           indtuples;              /* total number of tuples indexed */
        MemoryContext tmpCtx;           /* temporary memory context reset after each
                                                                 * tuple */
-       char            data[BLCKSZ];   /* cached page */
+       PGAlignedBlock data;            /* cached page */
        int                     count;                  /* number of tuples in cached page */
 } BloomBuildState;
 
@@ -52,7 +52,7 @@ flushCachedPage(Relation index, BloomBuildState *buildstate)
 
        state = GenericXLogStart(index);
        page = GenericXLogRegisterBuffer(state, buffer, GENERIC_XLOG_FULL_IMAGE);
-       memcpy(page, buildstate->data, BLCKSZ);
+       memcpy(page, buildstate->data.data, BLCKSZ);
        GenericXLogFinish(state);
        UnlockReleaseBuffer(buffer);
 }
@@ -63,8 +63,8 @@ flushCachedPage(Relation index, BloomBuildState *buildstate)
 static void
 initCachedPage(BloomBuildState *buildstate)
 {
-       memset(buildstate->data, 0, BLCKSZ);
-       BloomInitPage(buildstate->data, 0);
+       memset(buildstate->data.data, 0, BLCKSZ);
+       BloomInitPage(buildstate->data.data, 0);
        buildstate->count = 0;
 }
 
@@ -84,7 +84,7 @@ bloomBuildCallback(Relation index, HeapTuple htup, Datum *values,
        itup = BloomFormTuple(&buildstate->blstate, &htup->t_self, values, isnull);
 
        /* Try to add next item to cached page */
-       if (BloomPageAddItem(&buildstate->blstate, buildstate->data, itup))
+       if (BloomPageAddItem(&buildstate->blstate, buildstate->data.data, itup))
        {
                /* Next item was added successfully */
                buildstate->count++;
@@ -98,7 +98,7 @@ bloomBuildCallback(Relation index, HeapTuple htup, Datum *values,
 
                initCachedPage(buildstate);
 
-               if (!BloomPageAddItem(&buildstate->blstate, buildstate->data, itup))
+               if (!BloomPageAddItem(&buildstate->blstate, buildstate->data.data, itup))
                {
                        /* We shouldn't be here since we're inserting to the empty page */
                        elog(ERROR, "could not add new bloom tuple to empty page");
index fec62b1a5422369c5073f9551aba5f507e358712..d071402512790e779b4744ba3d88daacedc41c30 100644 (file)
@@ -37,7 +37,7 @@ typedef enum
        PREWARM_BUFFER
 } PrewarmType;
 
-static char blockbuffer[BLCKSZ];
+static PGAlignedBlock blockbuffer;
 
 /*
  * pg_prewarm(regclass, mode text, fork text,
@@ -179,7 +179,7 @@ pg_prewarm(PG_FUNCTION_ARGS)
                for (block = first_block; block <= last_block; ++block)
                {
                        CHECK_FOR_INTERRUPTS();
-                       smgrread(rel->rd_smgr, forkNumber, block, blockbuffer);
+                       smgrread(rel->rd_smgr, forkNumber, block, blockbuffer.data);
                        ++blocks_done;
                }
        }
index d5cc70258ac7a0d6d4744e5a749d01d1e29575f9..264f219d357d7d9e033615a6f0bcf7ceb6b2bac7 100644 (file)
@@ -616,7 +616,7 @@ entrySplitPage(GinBtree btree, Buffer origbuf,
        Page            lpage = PageGetTempPageCopy(BufferGetPage(origbuf));
        Page            rpage = PageGetTempPageCopy(BufferGetPage(origbuf));
        Size            pageSize = PageGetPageSize(lpage);
-       char            tupstore[2 * BLCKSZ];
+       PGAlignedBlock tupstore[2]; /* could need 2 pages' worth of tuples */
 
        entryPreparePage(btree, lpage, off, insertData, updateblkno);
 
@@ -625,7 +625,7 @@ entrySplitPage(GinBtree btree, Buffer origbuf,
         * one after another in a temporary workspace.
         */
        maxoff = PageGetMaxOffsetNumber(lpage);
-       ptr = tupstore;
+       ptr = tupstore[0].data;
        for (i = FirstOffsetNumber; i <= maxoff; i++)
        {
                if (i == off)
@@ -658,7 +658,7 @@ entrySplitPage(GinBtree btree, Buffer origbuf,
        GinInitPage(rpage, GinPageGetOpaque(lpage)->flags, pageSize);
        GinInitPage(lpage, GinPageGetOpaque(rpage)->flags, pageSize);
 
-       ptr = tupstore;
+       ptr = tupstore[0].data;
        maxoff++;
        lsize = 0;
 
index ff610ef218439c8e03dbdf3ab720cc62881cf6f7..144ca8b8e774287b33e64d14f3a451a1f1295143 100644 (file)
@@ -63,18 +63,15 @@ writeListPage(Relation index, Buffer buffer,
                                size = 0;
        OffsetNumber l,
                                off;
-       char       *workspace;
+       PGAlignedBlock workspace;
        char       *ptr;
 
-       /* workspace could be a local array; we use palloc for alignment */
-       workspace = palloc(BLCKSZ);
-
        START_CRIT_SECTION();
 
        GinInitBuffer(buffer, GIN_LIST);
 
        off = FirstOffsetNumber;
-       ptr = workspace;
+       ptr = workspace.data;
 
        for (i = 0; i < ntuples; i++)
        {
@@ -126,7 +123,7 @@ writeListPage(Relation index, Buffer buffer,
                XLogRegisterData((char *) &data, sizeof(ginxlogInsertListPage));
 
                XLogRegisterBuffer(0, buffer, REGBUF_WILL_INIT);
-               XLogRegisterBufData(0, workspace, size);
+               XLogRegisterBufData(0, workspace.data, size);
 
                recptr = XLogInsert(RM_GIN_ID, XLOG_GIN_INSERT_LISTPAGE);
                PageSetLSN(page, recptr);
@@ -139,8 +136,6 @@ writeListPage(Relation index, Buffer buffer,
 
        END_CRIT_SECTION();
 
-       pfree(workspace);
-
        return freesize;
 }
 
index 7b2906b0ca90476042706192133f3d67f5193c44..bbf98de35ac256d02de11bfd172f7ce0d58d3ce2 100644 (file)
@@ -998,7 +998,7 @@ static bool
 _hash_alloc_buckets(Relation rel, BlockNumber firstblock, uint32 nblocks)
 {
        BlockNumber lastblock;
-       char            zerobuf[BLCKSZ];
+       PGAlignedBlock zerobuf;
        Page            page;
        HashPageOpaque ovflopaque;
 
@@ -1011,7 +1011,7 @@ _hash_alloc_buckets(Relation rel, BlockNumber firstblock, uint32 nblocks)
        if (lastblock < firstblock || lastblock == InvalidBlockNumber)
                return false;
 
-       page = (Page) zerobuf;
+       page = (Page) zerobuf.data;
 
        /*
         * Initialize the page.  Just zeroing the page won't work; see
@@ -1032,11 +1032,11 @@ _hash_alloc_buckets(Relation rel, BlockNumber firstblock, uint32 nblocks)
                log_newpage(&rel->rd_node,
                                        MAIN_FORKNUM,
                                        lastblock,
-                                       zerobuf,
+                                       zerobuf.data,
                                        true);
 
        RelationOpenSmgr(rel);
-       smgrextend(rel->rd_smgr, MAIN_FORKNUM, lastblock, zerobuf, false);
+       smgrextend(rel->rd_smgr, MAIN_FORKNUM, lastblock, zerobuf.data, false);
 
        return true;
 }
index 608dc5a77f06c67f2a1e7aad8b5bdf3f7baecf6f..44d150f706f67787ec93351f07a1c0612da4986f 100644 (file)
@@ -2662,7 +2662,7 @@ heap_multi_insert(Relation relation, HeapTuple *tuples, int ntuples,
        HeapTuple  *heaptuples;
        int                     i;
        int                     ndone;
-       char       *scratch = NULL;
+       PGAlignedBlock scratch;
        Page            page;
        bool            needwal;
        Size            saveFreeSpace;
@@ -2679,14 +2679,6 @@ heap_multi_insert(Relation relation, HeapTuple *tuples, int ntuples,
                heaptuples[i] = heap_prepare_insert(relation, tuples[i],
                                                                                        xid, cid, options);
 
-       /*
-        * Allocate some memory to use for constructing the WAL record. Using
-        * palloc() within a critical section is not safe, so we allocate this
-        * beforehand.
-        */
-       if (needwal)
-               scratch = palloc(BLCKSZ);
-
        /*
         * We're about to do the actual inserts -- but check for conflict first,
         * to minimize the possibility of having to roll back work we've just
@@ -2779,7 +2771,7 @@ heap_multi_insert(Relation relation, HeapTuple *tuples, int ntuples,
                        uint8           info = XLOG_HEAP2_MULTI_INSERT;
                        char       *tupledata;
                        int                     totaldatalen;
-                       char       *scratchptr = scratch;
+                       char       *scratchptr = scratch.data;
                        bool            init;
                        int                     bufflags = 0;
 
@@ -2838,7 +2830,7 @@ heap_multi_insert(Relation relation, HeapTuple *tuples, int ntuples,
                                scratchptr += datalen;
                        }
                        totaldatalen = scratchptr - tupledata;
-                       Assert((scratchptr - scratch) < BLCKSZ);
+                       Assert((scratchptr - scratch.data) < BLCKSZ);
 
                        if (need_tuple_data)
                                xlrec->flags |= XLH_INSERT_CONTAINS_NEW_TUPLE;
@@ -2865,7 +2857,7 @@ heap_multi_insert(Relation relation, HeapTuple *tuples, int ntuples,
                                bufflags |= REGBUF_KEEP_DATA;
 
                        XLogBeginInsert();
-                       XLogRegisterData((char *) xlrec, tupledata - scratch);
+                       XLogRegisterData((char *) xlrec, tupledata - scratch.data);
                        XLogRegisterBuffer(0, buffer, REGBUF_STANDARD | bufflags);
 
                        XLogRegisterBufData(0, tupledata, totaldatalen);
index fc3ea13b5bd0eeaa961f58ced513ec11f96661c0..aa8cdec3505654169a389d09e25d4237bec10280 100644 (file)
@@ -645,10 +645,9 @@ static void
 vm_extend(Relation rel, BlockNumber vm_nblocks)
 {
        BlockNumber vm_nblocks_now;
-       Page            pg;
+       PGAlignedBlock pg;
 
-       pg = (Page) palloc(BLCKSZ);
-       PageInit(pg, BLCKSZ, 0);
+       PageInit((Page) pg.data, BLCKSZ, 0);
 
        /*
         * We use the relation extension lock to lock out other backends trying to
@@ -679,10 +678,10 @@ vm_extend(Relation rel, BlockNumber vm_nblocks)
        /* Now extend the file */
        while (vm_nblocks_now < vm_nblocks)
        {
-               PageSetChecksumInplace(pg, vm_nblocks_now);
+               PageSetChecksumInplace((Page) pg.data, vm_nblocks_now);
 
                smgrextend(rel->rd_smgr, VISIBILITYMAP_FORKNUM, vm_nblocks_now,
-                                  (char *) pg, false);
+                                  pg.data, false);
                vm_nblocks_now++;
        }
 
@@ -699,6 +698,4 @@ vm_extend(Relation rel, BlockNumber vm_nblocks)
        rel->rd_smgr->smgr_vm_nblocks = vm_nblocks_now;
 
        UnlockRelationForExtension(rel, ExclusiveLock);
-
-       pfree(pg);
 }
index 3adbf7b9494f00889afd0b98375dd15e4d9aa4fd..470ed887ce4ef826b8d93c46408cba6349ebb491 100644 (file)
@@ -61,14 +61,11 @@ typedef struct
 /* State of generic xlog record construction */
 struct GenericXLogState
 {
-       /*
-        * page's images. Should be first in this struct to have MAXALIGN'ed
-        * images addresses, because some code working with pages directly aligns
-        * addresses, not offsets from beginning of page
-        */
-       char            images[MAX_GENERIC_XLOG_PAGES * BLCKSZ];
+       /* Info about each page, see above */
        PageData        pages[MAX_GENERIC_XLOG_PAGES];
        bool            isLogged;
+       /* Page images (properly aligned) */
+       PGAlignedBlock images[MAX_GENERIC_XLOG_PAGES];
 };
 
 static void writeFragment(PageData *pageData, OffsetNumber offset,
@@ -251,12 +248,12 @@ computeDelta(PageData *pageData, Page curpage, Page targetpage)
 #ifdef WAL_DEBUG
        if (XLOG_DEBUG)
        {
-               char            tmp[BLCKSZ];
+               PGAlignedBlock tmp;
 
-               memcpy(tmp, curpage, BLCKSZ);
-               applyPageRedo(tmp, pageData->delta, pageData->deltaLen);
-               if (memcmp(tmp, targetpage, targetLower) != 0 ||
-                       memcmp(tmp + targetUpper, targetpage + targetUpper,
+               memcpy(tmp.data, curpage, BLCKSZ);
+               applyPageRedo(tmp.data, pageData->delta, pageData->deltaLen);
+               if (memcmp(tmp.data, targetpage, targetLower) != 0 ||
+                       memcmp(tmp.data + targetUpper, targetpage + targetUpper,
                                   BLCKSZ - targetUpper) != 0)
                        elog(ERROR, "result of generic xlog apply does not match");
        }
@@ -277,7 +274,7 @@ GenericXLogStart(Relation relation)
 
        for (i = 0; i < MAX_GENERIC_XLOG_PAGES; i++)
        {
-               state->pages[i].image = state->images + BLCKSZ * i;
+               state->pages[i].image = state->images[i].data;
                state->pages[i].buffer = InvalidBuffer;
        }
 
index e9a66aa70622f63b61e8c950512e9a1279c56fc5..651b0f3a84d96466c3d713f735a5ac71820c8765 100644 (file)
@@ -3182,8 +3182,7 @@ XLogFileInit(XLogSegNo logsegno, bool *use_existent, bool use_lock)
 {
        char            path[MAXPGPATH];
        char            tmppath[MAXPGPATH];
-       char            zbuffer_raw[XLOG_BLCKSZ + MAXIMUM_ALIGNOF];
-       char       *zbuffer;
+       PGAlignedXLogBlock zbuffer;
        XLogSegNo       installed_segno;
        XLogSegNo       max_segno;
        int                     fd;
@@ -3237,17 +3236,13 @@ XLogFileInit(XLogSegNo logsegno, bool *use_existent, bool use_lock)
         * fsync below) that all the indirect blocks are down on disk.  Therefore,
         * fdatasync(2) or O_DSYNC will be sufficient to sync future writes to the
         * log file.
-        *
-        * Note: ensure the buffer is reasonably well-aligned; this may save a few
-        * cycles transferring data to the kernel.
         */
-       zbuffer = (char *) MAXALIGN(zbuffer_raw);
-       memset(zbuffer, 0, XLOG_BLCKSZ);
+       memset(zbuffer.data, 0, XLOG_BLCKSZ);
        for (nbytes = 0; nbytes < XLogSegSize; nbytes += XLOG_BLCKSZ)
        {
                errno = 0;
                pgstat_report_wait_start(WAIT_EVENT_WAL_INIT_WRITE);
-               if ((int) write(fd, zbuffer, XLOG_BLCKSZ) != (int) XLOG_BLCKSZ)
+               if ((int) write(fd, zbuffer.data, XLOG_BLCKSZ) != (int) XLOG_BLCKSZ)
                {
                        int                     save_errno = errno;
 
@@ -3355,7 +3350,7 @@ XLogFileCopy(XLogSegNo destsegno, TimeLineID srcTLI, XLogSegNo srcsegno,
 {
        char            path[MAXPGPATH];
        char            tmppath[MAXPGPATH];
-       char            buffer[XLOG_BLCKSZ];
+       PGAlignedXLogBlock buffer;
        int                     srcfd;
        int                     fd;
        int                     nbytes;
@@ -3399,7 +3394,7 @@ XLogFileCopy(XLogSegNo destsegno, TimeLineID srcTLI, XLogSegNo srcsegno,
                 * zeros.
                 */
                if (nread < sizeof(buffer))
-                       memset(buffer, 0, sizeof(buffer));
+                       memset(buffer.data, 0, sizeof(buffer));
 
                if (nread > 0)
                {
@@ -3407,7 +3402,7 @@ XLogFileCopy(XLogSegNo destsegno, TimeLineID srcTLI, XLogSegNo srcsegno,
                                nread = sizeof(buffer);
                        errno = 0;
                        pgstat_report_wait_start(WAIT_EVENT_WAL_COPY_READ);
-                       if (read(srcfd, buffer, nread) != nread)
+                       if (read(srcfd, buffer.data, nread) != nread)
                        {
                                if (errno != 0)
                                        ereport(ERROR,
@@ -3423,7 +3418,7 @@ XLogFileCopy(XLogSegNo destsegno, TimeLineID srcTLI, XLogSegNo srcsegno,
                }
                errno = 0;
                pgstat_report_wait_start(WAIT_EVENT_WAL_COPY_WRITE);
-               if ((int) write(fd, buffer, sizeof(buffer)) != (int) sizeof(buffer))
+               if ((int) write(fd, buffer.data, sizeof(buffer)) != (int) sizeof(buffer))
                {
                        int                     save_errno = errno;
 
@@ -6410,8 +6405,11 @@ StartupXLOG(void)
        xlogreader->system_identifier = ControlFile->system_identifier;
 
        /*
-        * Allocate pages dedicated to WAL consistency checks, those had better be
-        * aligned.
+        * Allocate two page buffers dedicated to WAL consistency checks.  We do
+        * it this way, rather than just making static arrays, for two reasons:
+        * (1) no need to waste the storage in most instantiations of the backend;
+        * (2) a static char array isn't guaranteed to have any particular
+        * alignment, whereas palloc() will provide MAXALIGN'd storage.
         */
        replay_image_masked = (char *) palloc(BLCKSZ);
        master_image_masked = (char *) palloc(BLCKSZ);
index 3af03ecdb122f78cd6957c54a332bd4621bb7c86..1f86c907598be35a4534006e3c4f3e6086b5d9cc 100644 (file)
@@ -809,12 +809,12 @@ XLogCompressBackupBlock(char *page, uint16 hole_offset, uint16 hole_length,
        int32           len;
        int32           extra_bytes = 0;
        char       *source;
-       char            tmp[BLCKSZ];
+       PGAlignedBlock tmp;
 
        if (hole_length != 0)
        {
                /* must skip the hole */
-               source = tmp;
+               source = tmp.data;
                memcpy(source, page, hole_offset);
                memcpy(source + hole_offset,
                           page + (hole_offset + hole_length),
@@ -917,7 +917,7 @@ XLogSaveBufferForHint(Buffer buffer, bool buffer_std)
        if (lsn <= RedoRecPtr)
        {
                int                     flags;
-               char            copied_buffer[BLCKSZ];
+               PGAlignedBlock copied_buffer;
                char       *origdata = (char *) BufferGetBlock(buffer);
                RelFileNode rnode;
                ForkNumber      forkno;
@@ -935,11 +935,11 @@ XLogSaveBufferForHint(Buffer buffer, bool buffer_std)
                        uint16          lower = ((PageHeader) page)->pd_lower;
                        uint16          upper = ((PageHeader) page)->pd_upper;
 
-                       memcpy(copied_buffer, origdata, lower);
-                       memcpy(copied_buffer + upper, origdata + upper, BLCKSZ - upper);
+                       memcpy(copied_buffer.data, origdata, lower);
+                       memcpy(copied_buffer.data + upper, origdata + upper, BLCKSZ - upper);
                }
                else
-                       memcpy(copied_buffer, origdata, BLCKSZ);
+                       memcpy(copied_buffer.data, origdata, BLCKSZ);
 
                XLogBeginInsert();
 
@@ -948,7 +948,7 @@ XLogSaveBufferForHint(Buffer buffer, bool buffer_std)
                        flags |= REGBUF_STANDARD;
 
                BufferGetTag(buffer, &rnode, &forkno, &blkno);
-               XLogRegisterBlock(0, &rnode, forkno, blkno, copied_buffer, flags);
+               XLogRegisterBlock(0, &rnode, forkno, blkno, copied_buffer.data, flags);
 
                recptr = XLogInsert(RM_XLOG_ID, XLOG_FPI_FOR_HINT);
        }
index 8e83de6de5240b4b7c3a05021f0a142c44a3310a..2a2cbfb3fc874096c36efb776d4e3c7a43ef9ae0 100644 (file)
@@ -1404,7 +1404,7 @@ RestoreBlockImage(XLogReaderState *record, uint8 block_id, char *page)
 {
        DecodedBkpBlock *bkpb;
        char       *ptr;
-       char            tmp[BLCKSZ];
+       PGAlignedBlock tmp;
 
        if (!record->blocks[block_id].in_use)
                return false;
@@ -1417,7 +1417,7 @@ RestoreBlockImage(XLogReaderState *record, uint8 block_id, char *page)
        if (bkpb->bimg_info & BKPIMAGE_IS_COMPRESSED)
        {
                /* If a backup block image is compressed, decompress it */
-               if (pglz_decompress(ptr, bkpb->bimg_len, tmp,
+               if (pglz_decompress(ptr, bkpb->bimg_len, tmp.data,
                                                        BLCKSZ - bkpb->hole_length) < 0)
                {
                        report_invalid_record(record, "invalid compressed image at %X/%X, block %d",
@@ -1426,7 +1426,7 @@ RestoreBlockImage(XLogReaderState *record, uint8 block_id, char *page)
                                                                  block_id);
                        return false;
                }
-               ptr = tmp;
+               ptr = tmp.data;
        }
 
        /* generate page, taking into account hole if necessary */
index 6f1a429c7e5e828406ed27d41e0acff724346884..0b518cf6721990ac4c78ed618e12f7b8796eba95 100644 (file)
@@ -10820,21 +10820,14 @@ static void
 copy_relation_data(SMgrRelation src, SMgrRelation dst,
                                   ForkNumber forkNum, char relpersistence)
 {
-       char       *buf;
+       PGAlignedBlock buf;
        Page            page;
        bool            use_wal;
        bool            copying_initfork;
        BlockNumber nblocks;
        BlockNumber blkno;
 
-       /*
-        * palloc the buffer so that it's MAXALIGN'd.  If it were just a local
-        * char[] array, the compiler might align it on any byte boundary, which
-        * can seriously hurt transfer speed to and from the kernel; not to
-        * mention possibly making log_newpage's accesses to the page header fail.
-        */
-       buf = (char *) palloc(BLCKSZ);
-       page = (Page) buf;
+       page = (Page) buf.data;
 
        /*
         * The init fork for an unlogged relation in many respects has to be
@@ -10858,7 +10851,7 @@ copy_relation_data(SMgrRelation src, SMgrRelation dst,
                /* If we got a cancel signal during the copy of the data, quit */
                CHECK_FOR_INTERRUPTS();
 
-               smgrread(src, forkNum, blkno, buf);
+               smgrread(src, forkNum, blkno, buf.data);
 
                if (!PageIsVerified(page, blkno))
                        ereport(ERROR,
@@ -10884,11 +10877,9 @@ copy_relation_data(SMgrRelation src, SMgrRelation dst,
                 * rel, because there's no need for smgr to schedule an fsync for this
                 * write; we'll do it ourselves below.
                 */
-               smgrextend(dst, forkNum, blkno, buf, true);
+               smgrextend(dst, forkNum, blkno, buf.data, true);
        }
 
-       pfree(buf);
-
        /*
         * If the rel is WAL-logged, must fsync before commit.  We use heap_sync
         * to ensure that the toast table gets fsync'd too.  (For a temp or
index 3256db203e09cbe1a7875dea4be672c006edca38..37e44bd7f23ca172c4bf749f95af19800de935b5 100644 (file)
@@ -498,18 +498,18 @@ SendTimeLineHistory(TimeLineHistoryCmd *cmd)
        bytesleft = histfilelen;
        while (bytesleft > 0)
        {
-               char            rbuf[BLCKSZ];
+               PGAlignedBlock rbuf;
                int                     nread;
 
                pgstat_report_wait_start(WAIT_EVENT_WALSENDER_TIMELINE_HISTORY_READ);
-               nread = read(fd, rbuf, sizeof(rbuf));
+               nread = read(fd, rbuf.data, sizeof(rbuf));
                pgstat_report_wait_end();
                if (nread <= 0)
                        ereport(ERROR,
                                        (errcode_for_file_access(),
                                         errmsg("could not read file \"%s\": %m",
                                                        path)));
-               pq_sendbytes(&buf, rbuf, nread);
+               pq_sendbytes(&buf, rbuf.data, nread);
                bytesleft -= nread;
        }
        CloseTransientFile(fd);
index 4ca0ea4f2a343fc1bdd134a96be556252db5a4ca..01546da7cfff4706bc5469f8ea15651e59d16ed4 100644 (file)
@@ -87,7 +87,7 @@ struct BufFile
        off_t           curOffset;              /* offset part of current pos */
        int                     pos;                    /* next read/write position in buffer */
        int                     nbytes;                 /* total # of valid bytes in buffer */
-       char            buffer[BLCKSZ];
+       PGAlignedBlock buffer;
 };
 
 static BufFile *makeBufFile(File firstfile);
@@ -256,7 +256,7 @@ BufFileLoadBuffer(BufFile *file)
         * Read whatever we can get, up to a full bufferload.
         */
        file->nbytes = FileRead(thisfile,
-                                                       file->buffer,
+                                                       file->buffer.data,
                                                        sizeof(file->buffer),
                                                        WAIT_EVENT_BUFFILE_READ);
        if (file->nbytes < 0)
@@ -322,7 +322,7 @@ BufFileDumpBuffer(BufFile *file)
                        file->offsets[file->curFile] = file->curOffset;
                }
                bytestowrite = FileWrite(thisfile,
-                                                                file->buffer + wpos,
+                                                                file->buffer.data + wpos,
                                                                 bytestowrite,
                                                                 WAIT_EVENT_BUFFILE_WRITE);
                if (bytestowrite <= 0)
@@ -392,7 +392,7 @@ BufFileRead(BufFile *file, void *ptr, size_t size)
                        nthistime = size;
                Assert(nthistime > 0);
 
-               memcpy(ptr, file->buffer + file->pos, nthistime);
+               memcpy(ptr, file->buffer.data + file->pos, nthistime);
 
                file->pos += nthistime;
                ptr = (void *) ((char *) ptr + nthistime);
@@ -439,7 +439,7 @@ BufFileWrite(BufFile *file, void *ptr, size_t size)
                        nthistime = size;
                Assert(nthistime > 0);
 
-               memcpy(file->buffer + file->pos, ptr, nthistime);
+               memcpy(file->buffer.data + file->pos, ptr, nthistime);
 
                file->dirty = true;
                file->pos += nthistime;
index 3eee5b31aaa3c61b134b515dc7f4472f9e0f57da..42d2016570ff4db6728690a1d80a54c0dea9ec3d 100644 (file)
@@ -628,10 +628,9 @@ static void
 fsm_extend(Relation rel, BlockNumber fsm_nblocks)
 {
        BlockNumber fsm_nblocks_now;
-       Page            pg;
+       PGAlignedBlock pg;
 
-       pg = (Page) palloc(BLCKSZ);
-       PageInit(pg, BLCKSZ, 0);
+       PageInit((Page) pg.data, BLCKSZ, 0);
 
        /*
         * We use the relation extension lock to lock out other backends trying to
@@ -661,10 +660,10 @@ fsm_extend(Relation rel, BlockNumber fsm_nblocks)
 
        while (fsm_nblocks_now < fsm_nblocks)
        {
-               PageSetChecksumInplace(pg, fsm_nblocks_now);
+               PageSetChecksumInplace((Page) pg.data, fsm_nblocks_now);
 
                smgrextend(rel->rd_smgr, FSM_FORKNUM, fsm_nblocks_now,
-                                  (char *) pg, false);
+                                  pg.data, false);
                fsm_nblocks_now++;
        }
 
@@ -672,8 +671,6 @@ fsm_extend(Relation rel, BlockNumber fsm_nblocks)
        rel->rd_smgr->smgr_fsm_nblocks = fsm_nblocks_now;
 
        UnlockRelationForExtension(rel, ExclusiveLock);
-
-       pfree(pg);
 }
 
 /*
index d454fd1939fc7270533acb882d9214b4ee4d3d7a..4b946e1b496b00ac734545e03a82642e58399c00 100644 (file)
@@ -215,11 +215,11 @@ ltsWriteBlock(LogicalTapeSet *lts, long blocknum, void *buffer)
         */
        while (blocknum > lts->nBlocksWritten)
        {
-               char            zerobuf[BLCKSZ];
+               PGAlignedBlock zerobuf;
 
-               MemSet(zerobuf, 0, sizeof(zerobuf));
+               MemSet(zerobuf.data, 0, sizeof(zerobuf));
 
-               ltsWriteBlock(lts, lts->nBlocksWritten, zerobuf);
+               ltsWriteBlock(lts, lts->nBlocksWritten, zerobuf.data);
        }
 
        /* Write the requested block */
index 870b6d085e813045a2a18abd753226c2be30eac5..2953ba463dde3d96609fbe53464fe4b1cb5ba094 100644 (file)
@@ -115,18 +115,17 @@ dir_open_for_write(const char *pathname, const char *temp_suffix, size_t pad_to_
        /* Do pre-padding on non-compressed files */
        if (pad_to_size && dir_data->compression == 0)
        {
-               char       *zerobuf;
+               PGAlignedXLogBlock zerobuf;
                int                     bytes;
 
-               zerobuf = pg_malloc0(XLOG_BLCKSZ);
+               memset(zerobuf.data, 0, XLOG_BLCKSZ);
                for (bytes = 0; bytes < pad_to_size; bytes += XLOG_BLCKSZ)
                {
                        errno = 0;
-                       if (write(fd, zerobuf, XLOG_BLCKSZ) != XLOG_BLCKSZ)
+                       if (write(fd, zerobuf.data, XLOG_BLCKSZ) != XLOG_BLCKSZ)
                        {
                                int                     save_errno = errno;
 
-                               pg_free(zerobuf);
                                close(fd);
 
                                /*
@@ -136,7 +135,6 @@ dir_open_for_write(const char *pathname, const char *temp_suffix, size_t pad_to_
                                return NULL;
                        }
                }
-               pg_free(zerobuf);
 
                if (lseek(fd, 0, SEEK_SET) != 0)
                {
@@ -512,24 +510,20 @@ tar_write(Walfile f, const void *buf, size_t count)
 static bool
 tar_write_padding_data(TarMethodFile *f, size_t bytes)
 {
-       char       *zerobuf = pg_malloc0(XLOG_BLCKSZ);
+       PGAlignedXLogBlock zerobuf;
        size_t          bytesleft = bytes;
 
+       memset(zerobuf.data, 0, XLOG_BLCKSZ);
        while (bytesleft)
        {
-               size_t          bytestowrite = bytesleft > XLOG_BLCKSZ ? XLOG_BLCKSZ : bytesleft;
-
-               ssize_t         r = tar_write(f, zerobuf, bytestowrite);
+               size_t          bytestowrite = Min(bytesleft, XLOG_BLCKSZ);
+               ssize_t         r = tar_write(f, zerobuf.data, bytestowrite);
 
                if (r < 0)
-               {
-                       pg_free(zerobuf);
                        return false;
-               }
                bytesleft -= r;
        }
 
-       pg_free(zerobuf);
        return true;
 }
 
index ac678317795e82aea2ef783f02209d39588f6083..0e6d790246fc1722ac6696d7bd3ebed26cdf618e 100644 (file)
@@ -1129,7 +1129,7 @@ KillExistingArchiveStatus(void)
 static void
 WriteEmptyXLOG(void)
 {
-       char       *buffer;
+       PGAlignedXLogBlock buffer;
        XLogPageHeader page;
        XLogLongPageHeader longpage;
        XLogRecord *record;
@@ -1139,12 +1139,10 @@ WriteEmptyXLOG(void)
        int                     nbytes;
        char       *recptr;
 
-       /* Use malloc() to ensure buffer is MAXALIGNED */
-       buffer = (char *) pg_malloc(XLOG_BLCKSZ);
-       page = (XLogPageHeader) buffer;
-       memset(buffer, 0, XLOG_BLCKSZ);
+       memset(buffer.data, 0, XLOG_BLCKSZ);
 
        /* Set up the XLOG page header */
+       page = (XLogPageHeader) buffer.data;
        page->xlp_magic = XLOG_PAGE_MAGIC;
        page->xlp_info = XLP_LONG_HEADER;
        page->xlp_tli = ControlFile.checkPointCopy.ThisTimeLineID;
@@ -1190,7 +1188,7 @@ WriteEmptyXLOG(void)
        }
 
        errno = 0;
-       if (write(fd, buffer, XLOG_BLCKSZ) != XLOG_BLCKSZ)
+       if (write(fd, buffer.data, XLOG_BLCKSZ) != XLOG_BLCKSZ)
        {
                /* if write didn't set errno, assume problem is no disk space */
                if (errno == 0)
@@ -1201,11 +1199,11 @@ WriteEmptyXLOG(void)
        }
 
        /* Fill the rest of the file with zeroes */
-       memset(buffer, 0, XLOG_BLCKSZ);
+       memset(buffer.data, 0, XLOG_BLCKSZ);
        for (nbytes = XLOG_BLCKSZ; nbytes < XLogSegSize; nbytes += XLOG_BLCKSZ)
        {
                errno = 0;
-               if (write(fd, buffer, XLOG_BLCKSZ) != XLOG_BLCKSZ)
+               if (write(fd, buffer.data, XLOG_BLCKSZ) != XLOG_BLCKSZ)
                {
                        if (errno == 0)
                                errno = ENOSPC;
index a1b85f7706fbdbe320367b408f5da1e77cf6d338..ad8e407da22bc2e2d836249e7e2666290cc832b7 100644 (file)
@@ -158,7 +158,7 @@ recurse_dir(const char *datadir, const char *parentpath,
 static void
 rewind_copy_file_range(const char *path, off_t begin, off_t end, bool trunc)
 {
-       char            buf[BLCKSZ];
+       PGAlignedBlock buf;
        char            srcpath[MAXPGPATH];
        int                     srcfd;
 
@@ -184,7 +184,7 @@ rewind_copy_file_range(const char *path, off_t begin, off_t end, bool trunc)
                else
                        len = end - begin;
 
-               readlen = read(srcfd, buf, len);
+               readlen = read(srcfd, buf.data, len);
 
                if (readlen < 0)
                        pg_fatal("could not read file \"%s\": %s\n",
@@ -192,7 +192,7 @@ rewind_copy_file_range(const char *path, off_t begin, off_t end, bool trunc)
                else if (readlen == 0)
                        pg_fatal("unexpected EOF while reading file \"%s\"\n", srcpath);
 
-               write_target_range(buf, begin, readlen);
+               write_target_range(buf.data, begin, readlen);
                begin += readlen;
        }
 
index b8be9a5bda022bd98fcfd993a36d33a9e1ae62da..c9fd0316565c15c98ca74445e36d0692ee2888f4 100644 (file)
@@ -131,8 +131,8 @@ rewriteVisibilityMap(const char *fromfile, const char *tofile,
 {
        int                     src_fd;
        int                     dst_fd;
-       char       *buffer;
-       char       *new_vmbuf;
+       PGAlignedBlock buffer;
+       PGAlignedBlock new_vmbuf;
        ssize_t         totalBytesRead = 0;
        ssize_t         src_filesize;
        int                     rewriteVmBytesPerPage;
@@ -158,13 +158,6 @@ rewriteVisibilityMap(const char *fromfile, const char *tofile,
        /* Save old file size */
        src_filesize = statbuf.st_size;
 
-       /*
-        * Malloc the work buffers, rather than making them local arrays, to
-        * ensure adequate alignment.
-        */
-       buffer = (char *) pg_malloc(BLCKSZ);
-       new_vmbuf = (char *) pg_malloc(BLCKSZ);
-
        /*
         * Turn each visibility map page into 2 pages one by one. Each new page
         * has the same page header as the old one.  If the last section of the
@@ -180,7 +173,7 @@ rewriteVisibilityMap(const char *fromfile, const char *tofile,
                PageHeaderData pageheader;
                bool            old_lastblk;
 
-               if ((bytesRead = read(src_fd, buffer, BLCKSZ)) != BLCKSZ)
+               if ((bytesRead = read(src_fd, buffer.data, BLCKSZ)) != BLCKSZ)
                {
                        if (bytesRead < 0)
                                pg_fatal("error while copying relation \"%s.%s\": could not read file \"%s\": %s\n",
@@ -194,7 +187,7 @@ rewriteVisibilityMap(const char *fromfile, const char *tofile,
                old_lastblk = (totalBytesRead == src_filesize);
 
                /* Save the page header data */
-               memcpy(&pageheader, buffer, SizeOfPageHeaderData);
+               memcpy(&pageheader, buffer.data, SizeOfPageHeaderData);
 
                /*
                 * These old_* variables point to old visibility map page. old_cur
@@ -202,8 +195,8 @@ rewriteVisibilityMap(const char *fromfile, const char *tofile,
                 * old block.  old_break is the end+1 position on the old page for the
                 * data that will be transferred to the current new page.
                 */
-               old_cur = buffer + SizeOfPageHeaderData;
-               old_blkend = buffer + bytesRead;
+               old_cur = buffer.data + SizeOfPageHeaderData;
+               old_blkend = buffer.data + bytesRead;
                old_break = old_cur + rewriteVmBytesPerPage;
 
                while (old_break <= old_blkend)
@@ -213,12 +206,12 @@ rewriteVisibilityMap(const char *fromfile, const char *tofile,
                        bool            old_lastpart;
 
                        /* First, copy old page header to new page */
-                       memcpy(new_vmbuf, &pageheader, SizeOfPageHeaderData);
+                       memcpy(new_vmbuf.data, &pageheader, SizeOfPageHeaderData);
 
                        /* Rewriting the last part of the last old page? */
                        old_lastpart = old_lastblk && (old_break == old_blkend);
 
-                       new_cur = new_vmbuf + SizeOfPageHeaderData;
+                       new_cur = new_vmbuf.data + SizeOfPageHeaderData;
 
                        /* Process old page bytes one by one, and turn it into new page. */
                        while (old_cur < old_break)
@@ -252,11 +245,11 @@ rewriteVisibilityMap(const char *fromfile, const char *tofile,
 
                        /* Set new checksum for visibility map page, if enabled */
                        if (new_cluster.controldata.data_checksum_version != 0)
-                               ((PageHeader) new_vmbuf)->pd_checksum =
-                                       pg_checksum_page(new_vmbuf, new_blkno);
+                               ((PageHeader) new_vmbuf.data)->pd_checksum =
+                                       pg_checksum_page(new_vmbuf.data, new_blkno);
 
                        errno = 0;
-                       if (write(dst_fd, new_vmbuf, BLCKSZ) != BLCKSZ)
+                       if (write(dst_fd, new_vmbuf.data, BLCKSZ) != BLCKSZ)
                        {
                                /* if write didn't set errno, assume problem is no disk space */
                                if (errno == 0)
@@ -272,8 +265,6 @@ rewriteVisibilityMap(const char *fromfile, const char *tofile,
        }
 
        /* Clean up */
-       pg_free(buffer);
-       pg_free(new_vmbuf);
        close(dst_fd);
        close(src_fd);
 }
index d9f26fb6d0b0156552c65d571c11b53a4fbd5d09..59b2e18cb7f08543e4d18772d0193d6a55910a67 100644 (file)
@@ -969,6 +969,32 @@ typedef NameData *Name;
  * ----------------------------------------------------------------
  */
 
+/*
+ * Use this, not "char buf[BLCKSZ]", to declare a field or local variable
+ * holding a page buffer, if that page might be accessed as a page and not
+ * just a string of bytes.  Otherwise the variable might be under-aligned,
+ * causing problems on alignment-picky hardware.  (In some places, we use
+ * this to declare buffers even though we only pass them to read() and
+ * write(), because copying to/from aligned buffers is usually faster than
+ * using unaligned buffers.)  We include both "double" and "int64" in the
+ * union to ensure that the compiler knows the value must be MAXALIGN'ed
+ * (cf. configure's computation of MAXIMUM_ALIGNOF).
+ */
+typedef union PGAlignedBlock
+{
+       char            data[BLCKSZ];
+       double          force_align_d;
+       int64           force_align_i64;
+} PGAlignedBlock;
+
+/* Same, but for an XLOG_BLCKSZ-sized buffer */
+typedef union PGAlignedXLogBlock
+{
+       char            data[XLOG_BLCKSZ];
+       double          force_align_d;
+       int64           force_align_i64;
+} PGAlignedXLogBlock;
+
 /* msb for char */
 #define HIGHBIT                                        (0x80)
 #define IS_HIGHBIT_SET(ch)             ((unsigned char)(ch) & HIGHBIT)