Re: Calculating average block write time

On 11/18/22 09:51, Laurenz Albe wrote:
> On Fri, 2022-11-18 at 11:11 +0100, Thomas Kellerer wrote:
>> Thomas Kellerer schrieb am 04.11.2022 um 10:19:
>>> I can easily calculate the average block read time using
>>> pg_stat_database and divide blk_read_time by blks_read.
>>>
>>> While there is a column blk_write_time, it seems that there is no
>>> cummulative measure for the total number of blocks written.
>>>
>> Any ideas on how to get the equivalent of (blk_read_time / blks_read) for blk_write_time?
>>
>> I thought about using tup_updated + tup_inserted + tup_deleted because each tuple change would require at least one
blockwritten.
 
>> However, a single block write could update multiple tuples so the result of that wouldn't be accurate (too low).
> You cannot get that, because most writes are done by the checkpointer, and
> that does not distinguish between databases.

For a similar reason to why WAL files can't be be "single database" without 
significant rewrite?

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