Re: max_slot_wal_keep_size and wal_keep_segments

On 2020/07/17 20:24, David Steele wrote:
>
> On 7/17/20 5:11 AM, Fujii Masao wrote:
>>
>>
>> On 2020/07/14 20:30, David Steele wrote:
>>> On 7/14/20 12:00 AM, Fujii Masao wrote:
>>>>
>>>> The patch was no longer applied cleanly because of recent commit.
>>>> So I updated the patch. Attached.
>>>>
>>>> Barring any objection, I will commit this patch.
>>>
>>> This doesn't look right:
>>>
>>> +   the <xref linkend="guc-wal-keep-size"/> most recent megabytes
>>> +   WAL files plus one WAL file are
>>>
>>> How about:
>>>
>>> +   <xref linkend="guc-wal-keep-size"/> megabytes of
>>> +   WAL files plus one WAL file are
>>
>> Thanks for the comment! Isn't it better to keep "most recent" part?
>> If so, what about either of the followings?
>>
>> 1. <xref linkend="guc-wal-keep-size"/> megabytes of WAL files plus
>>      one WAL file that were most recently generated are kept all time.
>>
>> 2. <xref linkend="guc-wal-keep-size"/> megabytes + <xref linkend="guc-wal-segment-size"> bytes
>>      of WAL files that were most recently generated are kept all time.
>
> "most recent" seemed implied to me, but I see your point.
>
> How about:
>
> +   the most recent <xref linkend="guc-wal-keep-size"/> megabytes of
> +   WAL files plus one additional WAL file are

I adopted this and pushed the patch. Thanks!

Also we need to update the release note for v13. What about adding the following?

------------------------------------
Rename configuration parameter wal_keep_segments to wal_keep_size.

This allows how much WAL files to retain for the standby server, by bytes instead of the number of files.
If you previously used wal_keep_segments, the following formula will give you an approximately equivalent setting:

wal_keep_size = wal_keep_segments * wal_segment_size (typically 16MB)
------------------------------------

Regards,

--
Fujii Masao
Advanced Computing Technology Center
Research and Development Headquarters
NTT DATA CORPORATION