Messages in this thread | | | Date | Fri, 26 May 2006 09:19:39 +0800 | From | Wu Fengguang <> | Subject | Re: [PATCH 00/33] Adaptive read-ahead V12 |
| |
On Thu, May 25, 2006 at 08:44:15AM -0700, Andrew Morton wrote: > These are nice-looking numbers, but one wonders. If optimising readahead > makes this much difference to postgresql performance then postgresql should > be doing the readahead itself, rather than relying upon the kernel's > ability to guess what the application will be doing in the future. Because > surely the database can do a better job of that than the kernel. > > That would involve using posix_fadvise(POSIX_FADV_RANDOM) to disable kernel > readahead and then using posix_fadvise(POSIX_FADV_WILLNEED) to launch > application-level readahead. > > Has this been considered or attempted?
There has been many lengthy debates in the postgresql mailing list, and it seems that there has been _strong_ resistance to it.
IMHO, a best scheme would be - leave _obvious_ patterns to the kernel i.e. all kinds of (semi-)sequential reads - do fadvise() for _non-obvious_ patterns on _critical_ points i.e. the index scans
Wu - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
| |