Re: pg_dump's results have quite different size

On Thu, Dec 15, 2016 at 11:18 PM, Mark Kirkwood <
mark(dot)kirkwood(at)catalyst(dot)net(dot)nz> wrote:

> On 14/12/16 22:09, Oleksandr Shulgin wrote:
>
> On Wed, Dec 14, 2016 at 9:29 AM, Kaijiang Chen <chenkaijiang(at)gmail(dot)com
>> <mailto:chenkaijiang(at)gmail(dot)com>> wrote:
>>
>> Yes. The pg_dump quits with the message:
>>
>> pg_dump: Dumping the contents of table "data_histories" failed:
>> PQgetResult() failed.
>> pg_dump: Error message from server: ERROR: canceling statement
>> due to conflict with recovery
>> DETAIL: User query might have needed to see row versions that
>> must be removed.
>> pg_dump: The command was: COPY public.data_histories (id, user_id,
>> user_name, type, type_id, old_data, action, new_data, created_at,
>> updated_at) TO stdout;
>>
>>
>> Ah, then it's just that your backup script is broken: it should have
>> reported the error.
>>
>> Please do not top-post.
>>
>
> Oleksandr - how about a helpful response? E.g suggesting that maybe
> increasing max_standby_streaming_delay might help? Goddamn! folk asking for
> help deserve better than just being told 'it is broken dickhead'...
>

The problem *is* that his backups are broken without him knowing it. Maybe
increasing max_standby_streaming_delay is an answer, but maybe he would
rather have occasional broken backups *which he knows about* then suffer
the consequences of an increased max_standby_streaming_delay.
Maybe hot_standby_feedback would be a better option, or maybe
vacuum_defer_cleanup_age (but that is less likely).

The only thing we actually know with reasonable certainty is that his
backup script is broken, and that this is bad. Randomly changing settings
so that the brokenness is still there but just less obvious is more
dangerous than helpful.

Cheers,

Jeff