Hi! Thank you for your interesting for this patch!
I took a very brief look at this and was wondering if it was worth
having a way to make the per-table vacuum statistics opt-in (like a
table storage parameter) in order to decrease the shared memory
footprint of storing the stats.
I'm not sure how users can select tables that enable vacuum statistics
as I think they basically want to have statistics for all tables, but
I see your point. Since the size of PgStat_TableCounts approximately
tripled by this patch (112 bytes to 320 bytes), it might be worth
considering ways to reduce the number of entries or reducing the size
of vacuum statistics.
The main purpose of these statistics is to see abnormal behavior of vacuum in relation to a table or the database as a whole.
For example, there may be a situation where vacuum has started to run more often and spends a lot of resources on processing a certain index, but the size of the index does not change significantly. Moreover, the table in which this index is located can be much smaller in size. This may be because the index is bloated and needs to be reindexed.
This is exactly what vacuum statistics can show - we will see that compared to other objects, vacuum processed more blocks and spent more time on this index.
Perhaps the vacuum parameters for the index should be set more aggressively to avoid this in the future.
I suppose that if we turn off statistics collection for a certain object, we can miss it. In addition, the user may not enable the parameter for the object in time, because he will forget about it.
As for the second option, now I cannot say which statistics can be removed, to be honest. So far, they all seem necessary.
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Regards,
Alena Rybakina
Postgres Professional
