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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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76
src/backend/utils/misc/guc.c
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@ -10,7 +10,7 @@
* Written by Peter Eisentraut <peter_e@gmx.net>.
*
* IDENTIFICATION
* $PostgreSQL: pgsql/src/backend/utils/misc/guc.c,v 1.492 2009/01/09 10:13:18 mha Exp $
* $PostgreSQL: pgsql/src/backend/utils/misc/guc.c,v 1.493 2009/01/12 05:10:44 tgl Exp $
*
*--------------------------------------------------------------------
*/
@ -18,6 +18,7 @@
#include <ctype.h>
#include <float.h>
#include <math.h>
#include <limits.h>
#include <unistd.h>
#include <sys/stat.h>
@ -163,8 +164,9 @@ static bool assign_tcp_keepalives_count(int newval, bool doit, GucSource source)
static const char *show_tcp_keepalives_idle(void);
static const char *show_tcp_keepalives_interval(void);
static const char *show_tcp_keepalives_count(void);
static bool assign_autovacuum_max_workers(int newval, bool doit, GucSource source);
static bool assign_maxconnections(int newval, bool doit, GucSource source);
static bool assign_autovacuum_max_workers(int newval, bool doit, GucSource source);
static bool assign_effective_io_concurrency(int newval, bool doit, GucSource source);
static const char *assign_pgstat_temp_directory(const char *newval, bool doit, GucSource source);
static char *config_enum_get_options(struct config_enum *record,
@ -413,6 +415,7 @@ static int segment_size;
static int wal_block_size;
static int wal_segment_size;
static bool integer_datetimes;
static int effective_io_concurrency;
/* should be static, but commands/variable.c needs to get at these */
char *role_string;
@ -1700,6 +1703,20 @@ static struct config_int ConfigureNamesInt[] =
100, 0, 1000, NULL, NULL
},
{
{"effective_io_concurrency", PGC_USERSET, RESOURCES,
gettext_noop("Number of simultaneous requests that can be handled efficiently by the disk subsystem."),
gettext_noop("For RAID arrays, this should be approximately the number of drive spindles in the array.")
},
&effective_io_concurrency,
#ifdef USE_PREFETCH
1, 0, 1000,
#else
0, 0, 0,
#endif
assign_effective_io_concurrency, NULL
},
{
{"log_rotation_age", PGC_SIGHUP, LOGGING_WHERE,
gettext_noop("Automatic log file rotation will occur after N minutes."),
@ -7587,6 +7604,61 @@ assign_autovacuum_max_workers(int newval, bool doit, GucSource source)
return true;
}
static bool
assign_effective_io_concurrency(int newval, bool doit, GucSource source)
{
#ifdef USE_PREFETCH
double new_prefetch_pages = 0.0;
int i;
/*----------
* The user-visible GUC parameter is the number of drives (spindles),
* which we need to translate to a number-of-pages-to-prefetch target.
*
* The expected number of prefetch pages needed to keep N drives busy is:
*
* drives | I/O requests
* -------+----------------
* 1 | 1
* 2 | 2/1 + 2/2 = 3
* 3 | 3/1 + 3/2 + 3/3 = 5 1/2
* 4 | 4/1 + 4/2 + 4/3 + 4/4 = 8 1/3
* n | n * H(n)
*
* This is called the "coupon collector problem" and H(n) is called the
* harmonic series. This could be approximated by n * ln(n), but for
* reasonable numbers of drives we might as well just compute the series.
*
* Alternatively we could set the target to the number of pages necessary
* so that the expected number of active spindles is some arbitrary
* percentage of the total. This sounds the same but is actually slightly
* different. The result ends up being ln(1-P)/ln((n-1)/n) where P is
* that desired fraction.
*
* Experimental results show that both of these formulas aren't aggressive
* enough, but we don't really have any better proposals.
*
* Note that if newval = 0 (disabled), we must set target = 0.
*----------
*/
for (i = 1; i <= newval; i++)
new_prefetch_pages += (double) newval / (double) i;
/* This range check shouldn't fail, but let's be paranoid */
if (new_prefetch_pages >= 0.0 && new_prefetch_pages < (double) INT_MAX)
{
if (doit)
target_prefetch_pages = (int) rint(new_prefetch_pages);
return true;
}
else
return false;
#else
return true;
#endif /* USE_PREFETCH */
}
static const char *
assign_pgstat_temp_directory(const char *newval, bool doit, GucSource source)
{