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smgrzeroextend() uses FileFallocate() to efficiently extend files by multiple blocks. When extending by a small number of blocks, use FileZero() instead, as using posix_fallocate() for small numbers of blocks is inefficient for some file systems / operating systems. FileZero() is also used as the fallback for FileFallocate() on platforms / filesystems that don't support fallocate. A big advantage of using posix_fallocate() is that it typically won't cause dirty buffers in the kernel pagecache. So far the most common pattern in our code is that we smgrextend() a page full of zeroes and put the corresponding page into shared buffers, from where we later write out the actual contents of the page. If the kernel, e.g. due to memory pressure or elapsed time, already wrote back the all-zeroes page, this can lead to doubling the amount of writes reaching storage. There are no users of smgrzeroextend() as of this commit. That will follow in future commits. Reviewed-by: Melanie Plageman <melanieplageman@gmail.com> Reviewed-by: Heikki Linnakangas <hlinnaka@iki.fi> Reviewed-by: Kyotaro Horiguchi <horikyota.ntt@gmail.com> Reviewed-by: David Rowley <dgrowleyml@gmail.com> Reviewed-by: John Naylor <john.naylor@enterprisedb.com> Discussion: https://postgr.es/m/20221029025420.eplyow6k7tgu6he3@awork3.anarazel.de
55 lines
2.2 KiB
C
55 lines
2.2 KiB
C
/*-------------------------------------------------------------------------
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*
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* md.h
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* magnetic disk storage manager public interface declarations.
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*
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*
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* Portions Copyright (c) 1996-2023, PostgreSQL Global Development Group
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* Portions Copyright (c) 1994, Regents of the University of California
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*
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* src/include/storage/md.h
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*
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*-------------------------------------------------------------------------
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*/
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#ifndef MD_H
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#define MD_H
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#include "storage/block.h"
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#include "storage/relfilelocator.h"
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#include "storage/smgr.h"
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#include "storage/sync.h"
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/* md storage manager functionality */
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extern void mdinit(void);
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extern void mdopen(SMgrRelation reln);
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extern void mdclose(SMgrRelation reln, ForkNumber forknum);
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extern void mdcreate(SMgrRelation reln, ForkNumber forknum, bool isRedo);
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extern bool mdexists(SMgrRelation reln, ForkNumber forknum);
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extern void mdunlink(RelFileLocatorBackend rlocator, ForkNumber forknum, bool isRedo);
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extern void mdextend(SMgrRelation reln, ForkNumber forknum,
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BlockNumber blocknum, const void *buffer, bool skipFsync);
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extern void mdzeroextend(SMgrRelation reln, ForkNumber forknum,
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BlockNumber blocknum, int nblocks, bool skipFsync);
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extern bool mdprefetch(SMgrRelation reln, ForkNumber forknum,
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BlockNumber blocknum);
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extern void mdread(SMgrRelation reln, ForkNumber forknum, BlockNumber blocknum,
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void *buffer);
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extern void mdwrite(SMgrRelation reln, ForkNumber forknum,
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BlockNumber blocknum, const void *buffer, bool skipFsync);
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extern void mdwriteback(SMgrRelation reln, ForkNumber forknum,
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BlockNumber blocknum, BlockNumber nblocks);
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extern BlockNumber mdnblocks(SMgrRelation reln, ForkNumber forknum);
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extern void mdtruncate(SMgrRelation reln, ForkNumber forknum,
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BlockNumber nblocks);
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extern void mdimmedsync(SMgrRelation reln, ForkNumber forknum);
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extern void ForgetDatabaseSyncRequests(Oid dbid);
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extern void DropRelationFiles(RelFileLocator *delrels, int ndelrels, bool isRedo);
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/* md sync callbacks */
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extern int mdsyncfiletag(const FileTag *ftag, char *path);
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extern int mdunlinkfiletag(const FileTag *ftag, char *path);
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extern bool mdfiletagmatches(const FileTag *ftag, const FileTag *candidate);
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#endif /* MD_H */
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