diff options
Diffstat (limited to 'src/backend/storage/buffer/bufmgr.c')
| -rw-r--r-- | src/backend/storage/buffer/bufmgr.c | 74 |
1 files changed, 7 insertions, 67 deletions
diff --git a/src/backend/storage/buffer/bufmgr.c b/src/backend/storage/buffer/bufmgr.c index 58800542454..7a7748b6955 100644 --- a/src/backend/storage/buffer/bufmgr.c +++ b/src/backend/storage/buffer/bufmgr.c @@ -110,6 +110,13 @@ bool zero_damaged_pages = false; int bgwriter_lru_maxpages = 100; double bgwriter_lru_multiplier = 2.0; bool track_io_timing = false; + +/* + * How many buffers PrefetchBuffer callers should try to stay ahead of their + * ReadBuffer calls by. Zero means "never prefetch". This value is only used + * for buffers not belonging to tablespaces that have their + * effective_io_concurrency parameter set. + */ int effective_io_concurrency = 0; /* @@ -120,15 +127,6 @@ int checkpoint_flush_after = 0; int bgwriter_flush_after = 0; int backend_flush_after = 0; -/* - * How many buffers PrefetchBuffer callers should try to stay ahead of their - * ReadBuffer calls by. This is maintained by the assign hook for - * effective_io_concurrency. Zero means "never prefetch". This value is - * only used for buffers not belonging to tablespaces that have their - * effective_io_concurrency parameter set. - */ -int target_prefetch_pages = 0; - /* local state for StartBufferIO and related functions */ static BufferDesc *InProgressBuf = NULL; static bool IsForInput; @@ -462,64 +460,6 @@ static int ts_ckpt_progress_comparator(Datum a, Datum b, void *arg); /* - * ComputeIoConcurrency -- get the number of pages to prefetch for a given - * number of spindles. - */ -bool -ComputeIoConcurrency(int io_concurrency, double *target) -{ - double new_prefetch_pages = 0.0; - int i; - - /* - * Make sure the io_concurrency value is within valid range; it may have - * been forced with a manual pg_tablespace update. - */ - io_concurrency = Min(Max(io_concurrency, 0), MAX_IO_CONCURRENCY); - - /*---------- - * 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 target value is stashed in *extra and then assigned to the actual - * variable by assign_effective_io_concurrency. - * - * 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 io_concurrency = 0 (disabled), we must set target = 0. - *---------- - */ - - for (i = 1; i <= io_concurrency; i++) - new_prefetch_pages += (double) io_concurrency / (double) i; - - *target = new_prefetch_pages; - - /* This range check shouldn't fail, but let's be paranoid */ - return (new_prefetch_pages >= 0.0 && new_prefetch_pages < (double) INT_MAX); -} - -/* * PrefetchBuffer -- initiate asynchronous read of a block of a relation * * This is named by analogy to ReadBuffer but doesn't actually allocate a |