On 2017-02-22 03:05, Petr Jelinek wrote:
So to summarize attached patches:
0001 - Fixes performance issue where we build tons of snapshots that we
don't need which kills CPU.
0002 - Disables the use of ondisk historical snapshots for initial
consistent snapshot export as it may result in corrupt data. This
definitely needs backport.
0003 - Fixes bug where we might never reach snapshot on busy server due
to race condition in xl_running_xacts logging. The original use of
extra
locking does not seem to be enough in practice. Once we have agreed fix
for this it's probably worth backpatching. There are still some
comments
that need updating, this is more of a PoC.
I am not not entirely sure what to expect. Should a server with these 3
patches do initial data copy or not? The sgml seems to imply there is
not inital data copy. But my test does copy something.
Anyway, I have repeated the same old pgbench-test, assuming inital data
copy should be working.
With
0001-Skip-unnecessary-snapshot-builds.patch
0002-Don-t-use-on-disk-snapshots-for-snapshot-export-in-l.patch
0003-Fix-xl_running_xacts-usage-in-snapshot-builder.patch
the consistent (but wrong) end state is always that only one of the four
pgbench tables, pgbench_history, is replicated (always correctly).
Below is the output from the test (I've edited the lines for email)
(below, a,b,t,h stand for: pgbench_accounts, pgbench_branches,
pgbench_tellers, pgbench_history)
(master on port 6972, replica on port 6973.)
port
6972 a,b,t,h: 100000 1 10 347
6973 a,b,t,h: 0 0 0 347
a,b,t,h: a68efc81a 2c27f7ba5 128590a57 1e4070879 master
a,b,t,h: d41d8cd98 d41d8cd98 d41d8cd98 1e4070879 replica NOK
The md5-initstrings are from a md5 of the whole content of each table
(an ordered select *)
I repeated this a few times: of course, the number of rows in
pgbench_history varies a bit but otherwise it is always the same: 3
empty replica tables, pgbench_history replicated correctly.
Something is not right.
thanks,
Erik Rijkers
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