On Wed, 5 Feb 2020 at 21:36, Kirill Bychik <kirill.byc...@gmail.com> wrote: > > Hello pgsql-hackers, > > Submitting a patch that would enable gathering of per-statement WAL > generation statistics, similar to how it is done for buffer usage. > Collected is the number of records added to WAL and number of WAL > bytes written. > > The data collected was found valuable to analyze update-heavy load, > with WAL generation being the bottleneck. > > The usage data is collected at low level, after compression is done on > WAL record. Data is then exposed via pg_stat_statements, could also be > used in EXPLAIN ANALYZE if needed. Instrumentation is alike to the one > used for buffer stats. I didn't dare to unify both usage metric sets > into single struct, nor rework the way both are passed to parallel > workers. > > Performance impact is (supposed to be) very low, essentially adding > two int operations and memory access on WAL record insert. Additional > efforts to allocate shmem chunk for parallel workers. Parallel workers > shmem usage is increased to fir in a struct of two longs. > > Patch is separated in two parts: core changes and pg_stat_statements > additions. Essentially the extension has its schema updated to allow > two more fields, docs updated to reflect the change. Patch is prepared > against master branch. > > Please provide your comments and/or code findings.
I like the concept, I'm a big fan of anything that affordably improves visibility into Pg's I/O and activity. To date I've been relying on tools like systemtap to do this sort of thing. But that's a bit specialised, and Pg currently lacks useful instrumentation for it so it can be a pain to match up activity by parallel workers and that sort of thing. (I aim to find time to submit a patch for that.) I haven't yet reviewed the patch. -- Craig Ringer http://www.2ndQuadrant.com/ 2ndQuadrant - PostgreSQL Solutions for the Enterprise
