sorry for being so stupid: did you exclude antivirus/firewall related issue?
Le mer. 10 juin 2020 à 21:41, Mikkel Lauritsen <renard@tala.dk> a écrit :
Hi all,
I have a query that runs much slower in Postgres on Windows than on Linux, and I'm so far unable to explain why - the execution plans are identical and the hardware is reasonably the same caliber.
Using explain analyze on the database running on Windows I get
-> Index Scan using event_pkey on event t1 (cost=0.56..0.95 rows=1 width=295) (actual time=0.075..0.075 rows=0 loops=229227)
The server is Postgres 12, and for reasons outside of my control it runs on Windows 2012 on a virtual server. It has 4 cores and 32 GB ram allocated on a Xeon E5 4660 v4, and running winsat shows satisfactory disk and memory bandwidth and CPU performance.
If I copy the database to my laptop running Linux (Postgres 12 on Fedora 32, i7-9750H, 16 GB ram) I get the exact same execution plan. Explain analyze says
-> Index Scan using event_pkey on event t1 (cost=0.56..0.95 rows=1 width=295) (actual time=0.008..0.008 rows=0 loops=229227)
Note that the index scans are more than 9 times faster on my laptop, and the entire query executes about 12 times faster. I realize that each core in the laptop CPU is faster than a server core and that virtualization doesn't help performance, but I wouldn't expect that to make the Windows box 10 times slower.
The table is freshly vacuumed. It has about 10M rows and takes about 2.6G disk space; the index is about 600M. Everything is cached; there's basically no disk I/O happening while the query is executing.
The only Postgres configuration difference between the Windows and Linux environments is shared_buffers, which is 4G on my laptop and 512M on the Windows server, and effective_cache_size which are 8G on the laptop and 16G on the server.
I suspect that something is rotten in for example the provisioning of the virtualization environment, but before I start pestering the operations people I would really appreciate any comments on whether the performance difference is to be expected or if there's some obvious tuning to try.
