On 4/25/19 12:47 PM, Martin Kováčik wrote:
As my example shows you don't have to import a lot of rows - 1000 is
enough to make a difference - it all depends on the query. When a
cartesian product is involved only a few records is enough.
I think that stats should be MVCC versioned otherwise the planner is
using wrong statistics and chooses wrong plans.
Then you are looking at moving the choke point to looking up the correct
stats across possibly hundreds/thousands of transactions in flight.
*Martin Kováčik*
/CEO/
*redByte*, s.r.o.
+421 904 236 791
kovacik@xxxxxxxxxx <mailto:kovacik@xxxxxxxxxx>, www.redbyte.eu
<http://redbyte.eu>
On Thu, Apr 25, 2019 at 9:28 PM Michael Lewis <mlewis@xxxxxxxxxxx
<mailto:mlewis@xxxxxxxxxxx>> wrote:
On Thu, Apr 25, 2019, 11:34 AM Martin Kováčik <kovacik@xxxxxxxxxx
<mailto:kovacik@xxxxxxxxxx>> wrote:
Turning off autovacuum for the tests is a valid option and I
will definitely do this as a workaround. Each test pretty much
starts with empty schema and data for it is generated during the
run and rolled back at the end. I have a lot of tests and at the
moment it is not feasible to modify them.
The real workload for the application is different, but there
are some cases, when we import data from remote web service in a
transaction do some work with it and then we do a commit. If
there is an autovacuum during this process I assume there will
be similar problem regarding planner statistics.
Unless you are importing a huge amount of data relative to what is
already there, it seems likely to be significantly less impactful
than adding data to a completely empty table. The stats on a table
with 0 rows and then 5000 rows is going to be night and day, while
the difference between stats on 100,000 rows and 105,000 is not as
impactful. Musing here. I expect others will chime in.
Stats are not versioned with MVCC so it would expected that a commit
in another transaction that is updating stats would influence the
query plan for another transaction that is active.
--
Adrian Klaver
adrian.klaver@xxxxxxxxxxx
