diff options
Diffstat (limited to 'src/backend/access/transam/clog.c')
| -rw-r--r-- | src/backend/access/transam/clog.c | 29 |
1 files changed, 11 insertions, 18 deletions
diff --git a/src/backend/access/transam/clog.c b/src/backend/access/transam/clog.c index 06aff181d8d..263447679b8 100644 --- a/src/backend/access/transam/clog.c +++ b/src/backend/access/transam/clog.c @@ -417,30 +417,23 @@ TransactionIdGetStatus(TransactionId xid, XLogRecPtr *lsn) /* * Number of shared CLOG buffers. * - * Testing during the PostgreSQL 9.2 development cycle revealed that on a - * large multi-processor system, it was possible to have more CLOG page - * requests in flight at one time than the number of CLOG buffers which existed - * at that time, which was hardcoded to 8. Further testing revealed that - * performance dropped off with more than 32 CLOG buffers, possibly because - * the linear buffer search algorithm doesn't scale well. + * On larger multi-processor systems, it is possible to have many CLOG page + * requests in flight at one time which could lead to disk access for CLOG + * page if the required page is not found in memory. Testing revealed that we + * can get the best performance by having 128 CLOG buffers, more than that it + * doesn't improve performance. * - * Unconditionally increasing the number of CLOG buffers to 32 did not seem - * like a good idea, because it would increase the minimum amount of shared - * memory required to start, which could be a problem for people running very - * small configurations. The following formula seems to represent a reasonable + * Unconditionally keeping the number of CLOG buffers to 128 did not seem like + * a good idea, because it would increase the minimum amount of shared memory + * required to start, which could be a problem for people running very small + * configurations. The following formula seems to represent a reasonable * compromise: people with very low values for shared_buffers will get fewer - * CLOG buffers as well, and everyone else will get 32. - * - * It is likely that some further work will be needed here in future releases; - * for example, on a 64-core server, the maximum number of CLOG requests that - * can be simultaneously in flight will be even larger. But that will - * apparently require more than just changing the formula, so for now we take - * the easy way out. + * CLOG buffers as well, and everyone else will get 128. */ Size CLOGShmemBuffers(void) { - return Min(32, Max(4, NBuffers / 512)); + return Min(128, Max(4, NBuffers / 512)); } /* |