Curtis Faith wrote: > Good points. > > Now for some surprising news (at least it surprised me). > > I researched the file system source on my system (FreeBSD 4.6) and found > that the behavior was optimized for non-database access to eliminate > unnecessary writes when temp files are created and deleted rapidly. It was > not optimized to get data to the disk in the most efficient manner. > > The syncer on FreeBSD appears to place dirtied filesystem buffers into > work queues that range from 1 to SYNCER_MAXDELAY. Each second the syncer > processes one of the queues and increments a counter syncer_delayno. > > On my system the setting for SYNCER_MAXDELAY is 32. So each second 1/32nd > of the writes that were buffered are processed. If the syncer gets behind > and the writes for a given second exceed one second to process the syncer > does not wait but begins processing the next queue. > > AFAICT this means that there is no opportunity to have writes combined by > the disk since they are processed in buckets based on the time the writes > came in.
This is the trickle syncer. It prevents bursts of disk activity every 30 seconds. It is for non-fsync writes, of course, and I assume if the kernel buffers get low, it starts to flush faster. -- Bruce Momjian | http://candle.pha.pa.us [EMAIL PROTECTED] | (610) 359-1001 + If your life is a hard drive, | 13 Roberts Road + Christ can be your backup. | Newtown Square, Pennsylvania 19073 ---------------------------(end of broadcast)--------------------------- TIP 5: Have you checked our extensive FAQ? http://www.postgresql.org/users-lounge/docs/faq.html
