Hi, On 2017-04-24 21:17:43 -0700, Andres Freund wrote: > I've lately seen more and more installations where the generation of > write-ahead-log (WAL) is one of the primary bottlenecks. I'm curious > whether that's primarily a "sampling error" of mine, or whether that's > indeed more common. > > The primary reason I'm curious is that I'm pondering a few potential > optimizations, and would like to have some guidance which are more and > which are less important. > > Questions (answer as many you can comfortably answer): > - How many MB/s, segments/s do you see on busier servers? > - What generates the bulk of WAL on your servers (9.5+ can use > pg_xlogdump --stats to compute that)? > - Are you seeing WAL writes being a bottleneck?OA > - What kind of backup methods are you using and is the WAL volume a > problem? > - What kind of replication are you using and is the WAL volume a > problem? > - What are your settings for wal_compression, max_wal_size (9.5+) / > checkpoint_segments (< 9.5), checkpoint_timeout and wal_buffers? > - Could you quickly describe your workload? Ok, based on the, few, answers I've got so far, my experience is indeed skewed. A number of the PG users I interacted with over the last couple years had WAL write ranges somewhere in the range of 500MB/s to 2.2GB/s (max I'veseen). At that point WAL insertion became a major bottleneck, even if storage was more than fast enough to keep up. To address these we'd need some changes, but the feedback so far suggest that it's not yet a widespread issue... - Andres -- Sent via pgsql-performance mailing list (pgsql-performance@xxxxxxxxxxxxxx) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-performance
