On 2016-01-11 14:45:16 +0100, Andres Freund wrote:
I measured it in a different number of cases, both on SSDs and spinning
rust. I just reproduced it with:
-D /srv/temp/pgdev-dev-800/ \
-c maintenance_work_mem=2GB \
-c fsync=on \
-c synchronous_commit=off \
-c shared_buffers=2GB \
-c wal_level=hot_standby \
-c max_wal_senders=10 \
-c max_wal_size=100GB \
What kernel, filesystem and filesystem option did you measure with?
Andres did these measures, not me, so I do not know.
I was/am using ext4, and it turns out that, when abling flushing, the
results are hugely dependant on barriers=on/off, with the latter making
flushing rather advantageous. Additionally data=ordered/writeback makes
measureable difference too.
These are very interesting tests, I'm looking forward to have a look at
The fact that these options change performance is expected. Personnaly the
test I submitted on the thread used ext4 with default mount options plus
If I had a choice, I would tend to take the safest options, because the
point of a database is to keep data safe. That's why I'm not found of the
"synchronous_commit=off" chosen above.
Reading kernel sources trying to understand some more of the performance
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