Re: Introduce XID age and inactive timeout based replication slot invalidation

On Wed, Mar 6, 2024 at 2:47 PM Bharath Rupireddy
<bharath(dot)rupireddyforpostgres(at)gmail(dot)com> wrote:
>
> Thanks. v8-0001 is how it looks. Please see the v8 patch set with this change.
>

Commit message says: "Currently postgres has the ability to invalidate
inactive replication slots based on the amount of WAL (set via
max_slot_wal_keep_size GUC) that will be needed for the slots in case
they become active. However, choosing a default value for
max_slot_wal_keep_size is tricky. Because the amount of WAL a customer
generates, and their allocated storage will vary greatly in
production, making it difficult to pin down a one-size-fits-all value.
It is often easy for developers to set an XID age (age of slot's xmin
or catalog_xmin) of say 1 or 1.5 billion, after which the slots get
invalidated."

I don't see how it will be easier for the user to choose the default
value of 'max_slot_xid_age' compared to 'max_slot_wal_keep_size'. But,
I agree similar to 'max_slot_wal_keep_size', 'max_slot_xid_age' can be
another parameter to allow vacuum to proceed removing the rows which
otherwise it wouldn't have been as those would be required by some
slot. Now, if this understanding is correct, we should probably make
this invalidation happen by (auto)vacuum after computing the age based
on this new parameter.

--
With Regards,
Amit Kapila.