Am Donnerstag, 19. November 2009 13:29:56 schrieb Craig Ringer: > On 19/11/2009 12:22 PM, Scott Carey wrote: > > 3: Have PG wait a half second (configurable) after the checkpoint > > fsync() completes before deleting/ overwriting any WAL segments. This > > would be a trivial "feature" to add to a postgres release, I think. > > How does that help? It doesn't provide any guarantee that the data has > hit main storage - it could lurk in SDD cache for hours. > > > 4: Yet another solution: The drives DO adhere to write barriers > > properly. A filesystem that used these in the process of fsync() would be > > fine too. So XFS without LVM or MD (or the newer versions of those that > > don't ignore barriers) would work too. > > *if* the WAL is also on the SSD. > > If the WAL is on a separate drive, the write barriers do you no good, > because they won't ensure that the data hits the main drive storage > before the WAL recycling hits the WAL disk storage. The two drives > operate independently and the write barriers don't interact. > > You'd need some kind of inter-drive write barrier. > > -- > Craig Ringer Hello ! as i understand this: ssd performace is great, but caching is the problem. questions: 1. what about conventional disks with 32/64 mb cache ? how do they handle the plug test if their caches are on ? 2. what about using seperated power supply for the disks ? it it possible to write back the cache after switching the sata to another machine controller ? 3. what about making a statement about a lacking enterprise feature (aka emergency battery equipped ssd) and submitting this to the producers ? I found that one of them (OCZ) seems to handle suggestions of customers (see write speed discussins on vertex fro example) and another (intel) seems to handle serious problems with his disks in rewriting and sometimes redesigning his products - if you tell them and market dictades to react (see degeneration of performace before 1.11 firmware). perhaps its time to act and not only to complain about the fact. (btw: found funny bonnie++ for my intel 160 gb postville and my samsung pb22 after using the sam for now approx. 3 months+ ... my conclusion: NOT all SSD are equal ...) best regards anton -- ATRSoft GmbH Bivetsweg 12 D 41542 Dormagen Deutschland Tel .: +49(0)2182 8339951 Mobil: +49(0)172 3490817 Geschäftsführer Anton Rommerskirchen Köln HRB 44927 STNR 122/5701 - 2030 USTID DE213791450 -- Sent via pgsql-performance mailing list (pgsql-performance@xxxxxxxxxxxxxx) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-performance
