Re: max_wal_size

On 27.05.2020 13:16, Andreas Kretschmer wrote:
>
> Am 27.05.20 um 12:11 schrieb Pavel Luzanov:
>> Hello,
>>
>> About parameter max_wal_size the documentation 
>> <https://www.postgresql.org/docs/current/runtime-config-wal.html#GUC-MAX-WAL-SIZE> 
>> says: "Maximum size to let the WAL grow to between automatic WAL 
>> checkpoints."
>> Is it correct?
>>
>> The size between automatic WAL checkpoints or the size of all WAL 
>> files in the pg_wal directory?
>
> size between checkpoints, size of all wal's can be higher, see 
> wal_keep_segments.
>

It is clear that total size can be higher due to wal_keep_segments, 
replications slots, archive_command etc.

But does max_wal_size relate to the (a) two subsequent checkpoints (as 
you may read the wording in the docs) or (b) to the past completed 
checkpoint AND the current yet-uncompleted checkpoint (which together 
may be up to TWO checkpoint intervals)?

If I read CalculateCheckpointSegments() in xlog.c correctly, the answer 
is (b), and hence the documentation is misleading.

Regards,
Egor.