diff options
Diffstat (limited to 'src/backend/utils/misc/guc.c')
| -rw-r--r-- | src/backend/utils/misc/guc.c | 76 |
1 files changed, 74 insertions, 2 deletions
diff --git a/src/backend/utils/misc/guc.c b/src/backend/utils/misc/guc.c index 8d927ae1387..63e9628a5dc 100644 --- a/src/backend/utils/misc/guc.c +++ b/src/backend/utils/misc/guc.c @@ -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; @@ -1701,6 +1704,20 @@ static struct config_int ConfigureNamesInt[] = }, { + {"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."), NULL, @@ -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) { |