> On Nov 2, 2017, at 9:34 AM, Mark Fletcher <ma...@corp.groups.io> wrote:
>
> Hello,
>
> Running Postgres 9.6.5, we're using logical decoding to take changes to the
> database and propagate them elsewhere in our system. We are using the PGX Go
> Postgres library, at https://github.com/jackc/pgx, and we are using the
> test_decoding plugin to format the changes. We are using 6 slots/have 6
> processes streaming the changes from our database.
>
> This setup works great, except that every 20 hours or so, some or all of the
> processes encounter a problem, all at the same time. They receive an
> unexpected message type 'w'. At this point the processes restart, and when
> they do, they encounter another error: "ERROR: got sequence entry 0 for toast
> chunk 20559160 instead of seq 6935 (SQLSTATE XX000)" (the chunk number/seq
> number varies). This causes them to restart again. They will encounter the
> sequence entry error up to 3 more times, before things magically start to
> work again.
>
> We are also doing standard streaming replication to a slave off this
> database, and that has never seen a problem.
>
> Does this ring a bell for anyone? Do you have any suggestions for how I
> should go about figuring out what's happening?
Where are the errors coming from - your code or pgx? If it's from pgx, what's
the exact error? ('w' is regular replication payload data, so it'd be expected
as a copydata payload message type, but would be an error for a replication
message).
Do you capture the raw data from the replication connection when the error
happens?
(If you're using pgx you might be interested in
https://github.com/wttw/pgoutput - it's support for the pgoutput logical
decoder in PG10, which might be a bit more robust to deal with than the
test_decoding one).
Cheers,
Steve
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