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Implement prefetching via posix_fadvise() for bitmap index scans. A new

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GUC variable effective_io_concurrency controls how many concurrent block
prefetch requests will be issued.

(The best way to handle this for plain index scans is still under debate,
so that part is not applied yet --- tgl)

Greg Stark
This commit is contained in:
Tom Lane
2009-01-12 05:10:45 +00:00
parent 1a37056a74
commit b7b8f0b609
15 changed files with 422 additions and 17 deletions
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38
src/backend/storage/file/fd.c
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@ -7,7 +7,7 @@
* Portions Copyright (c) 1994, Regents of the University of California
*
* IDENTIFICATION
* $PostgreSQL: pgsql/src/backend/storage/file/fd.c,v 1.146 2009/01/01 17:23:47 momjian Exp $
* $PostgreSQL: pgsql/src/backend/storage/file/fd.c,v 1.147 2009/01/12 05:10:44 tgl Exp $
*
* NOTES:
*
@ -1029,6 +1029,42 @@ FileClose(File file)
FreeVfd(file);
}
/*
* FilePrefetch - initiate asynchronous read of a given range of the file.
* The logical seek position is unaffected.
*
* Currently the only implementation of this function is using posix_fadvise
* which is the simplest standardized interface that accomplishes this.
* We could add an implementation using libaio in the future; but note that
* this API is inappropriate for libaio, which wants to have a buffer provided
* to read into.
*/
int
FilePrefetch(File file, off_t offset, int amount)
{
#if defined(USE_POSIX_FADVISE) && defined(POSIX_FADV_WILLNEED)
int returnCode;
Assert(FileIsValid(file));
DO_DB(elog(LOG, "FilePrefetch: %d (%s) " INT64_FORMAT " %d",
file, VfdCache[file].fileName,
(int64) offset, amount));
returnCode = FileAccess(file);
if (returnCode < 0)
return returnCode;
returnCode = posix_fadvise(VfdCache[file].fd, offset, amount,
POSIX_FADV_WILLNEED);
return returnCode;
#else
Assert(FileIsValid(file));
return 0;
#endif
}
int
FileRead(File file, char *buffer, int amount)
{