Re: What exactly is postgres doing during INSERT/UPDATE ?
Aidan Van Dyk <aidan@highrise.ca>
From: Aidan Van Dyk <aidan@highrise.ca>
To: Merlin Moncure <mmoncure@gmail.com>
Cc: Greg Stark <gsstark@mit.edu>, Mark Mielke <mark@mark.mielke.cc>, Scott Marlowe <scott.marlowe@gmail.com>, Luke Koops <luke.koops@entrust.com>, Joseph S <jks@selectacast.net>, "pgsql-performance@postgresql.org" <pgsql-performance@postgresql.org>
Date: 2009-08-31T14:48:09Z
Lists: pgsql-performance
* Merlin Moncure <mmoncure@gmail.com> [090831 10:38]: > I agree, that's good analysis. The main point I was making was that > if you have say a 10 disk raid 5, you don't involve 10 disks, only > two...a very common misconception. I made another mistake that you > didn't catch: you need to read *both* the data drive and the parity > drive before writing, not just the parity drive. > > I wonder if flash SSD are a better fit for raid 5 since the reads are > much cheaper than writes and there is no rotational latency. (also, > $/gb is different, and so are the failure cases). The other thing that scares me about raid-5 is the write-hole, and the possible delayed inconsistency that brings... Again, hopefully mitigated by a dependable controller w/ BBU... -- Aidan Van Dyk Create like a god, aidan@highrise.ca command like a king, http://www.highrise.ca/ work like a slave.