Hi, a little off the general topic but I am just wondering if the “tar -cf - pgdata | wc -c” trick can be used as general trick to pre-warm the cache?
Thanks. On Oct 9, 2014, at 10:55 AM, Jeff Janes <jeff.ja...@gmail.com> wrote: > On Thu, Oct 9, 2014 at 3:52 AM, pinker <pin...@onet.eu> wrote: > Hello All, > I have a brand new machine to tune: > x3750 M4, 4xE5-4640v2 2.2GHz; 512GBRAM (32x16GB), 4x300GB > SAS + SSD (Easy Tier) in RAID 10 > > What's particularly important now is to choose optimal configuration for > write operations. We have discussion about checkpoint_segments and > checkpoint_timeout parameters. Test, which was based on pg_replay, has shown > that the biggest amount of data is written when checkpoint_segments are set > to 10 000 and checkpoint_timeout to 30 min, but I'm worrying about amount of > time needed for crash recovery. > > Since you already have pg_replay running, kill -9 some backend (my favorite > victim is the bgwriter) during the middle of pg_replay, and see how long it > takes to recover. > > You might want to try it with and without clobbering the FS cache, or simply > rebooting the whole machine, depending on what kind of crash you think is > more likely. > > Recovering into a cold cache can be painfully slow. If your database mostly > fits in memory, you can speed it up by using something (like "tar -cf - > pgdata | wc -c" to) read the entire pg data directory in sequential fashion > and hopefully cache it. If you find recovery too slow, you might want to try > to this trick (and put it in your init scripts) rather than lowering > checkpoint_segments. > > Cheers, > > Jeff >
