MIME-Version: 1.0
References: <CAD21AoAd0BX0L17YxSCbSNbj=3V7dvLVGY0WhwLHAt724rNCZA@mail.gmail.com>
 <ZgulmKzdqxuBuhCU@ip-10-97-1-34.eu-west-3.compute.internal>
 <CAJpy0uBthb-RG=Xg+mM-G6Xy01JLcBsizJuz+xbti08qP_W7AQ@mail.gmail.com>
 <CALj2ACVfDBcbybgyga7ia_KiQPAfEi_3=VDOGf2VU8RkJZSQpw@mail.gmail.com>
 <Zg0QgarM9UlRutLw@ip-10-97-1-34.eu-west-3.compute.internal>
 <CALj2ACUmp-F+irHYfNhmo_9yaCo7aGi7ZB20KQcDR3S9eT56hg@mail.gmail.com>
 <Zg1WqRS/gQrLG2vl@ip-10-97-1-34.eu-west-3.compute.internal>
 <CALj2ACUBiRLHF7VYD-0nYVHSvVBSCQ_5OMbP4tE8Ys_rpvQ--A@mail.gmail.com>
 <Zg2DgfXorAXrC8lw@ip-10-97-1-34.eu-west-3.compute.internal>
 <CALj2ACXbUzp-9tixeUK_dws5k+ARJaXxj8cj9W3adA0XNUS4Hg@mail.gmail.com>
 <Zg+rvmqjL3DfbJdx@ip-10-97-1-34.eu-west-3.compute.internal>
 <CALj2ACW8SYiRL8vGAhez=FdrzxO0W5pVFvN8GF7yKCO8_c=QdQ@mail.gmail.com>
 <CAA4eK1+-ipXB+LuUiDNQ5L+sWJFpzK89k-Oc7xOG37AefrptoQ@mail.gmail.com>
 <CALj2ACWhTY9mRc7sOpuao=GGidRjCVXc0SNtJ_DNman4nh5CcQ@mail.gmail.com>
 <CALj2ACVY+Fd5vC0VjW=5VDK9mmt-Y+PDZxnBp8ngGAZc24Vv9g@mail.gmail.com>
 <CALj2ACX0FVrx9f0c2g19Rb-WAJhm3wdyttde3YQtkotL6bUveA@mail.gmail.com>
 <CALj2ACXQNGXokgx8APwdxrG4MHMF=cOz6XQtUL7EHua9oUfkgA@mail.gmail.com>
 <CAFPTHDZPOc7pY4E0zJ2om0MZLMt+UuiX-VLsJyRO_aSyR8DsnA@mail.gmail.com>
 <CALj2ACVu0EJ+QQ7W0oHbL_+hCtk+p-00MNhE4hfjFcXaMepMfg@mail.gmail.com>
 <CAA4eK1KVbicrQQbMLEQiHEi9=VJpxrErrK7CiMamwaMPfff3WA@mail.gmail.com>
 <CALj2ACXe8+xSNdMXTMaSRWUwX7v61Ad4iddUwnn=djSwx3GLLg@mail.gmail.com>
 <CAHut+PuFzCHPCiZbpoQX59kgZbebuWT0gR0O7rOe4t_sdYu=OA@mail.gmail.com> <CALj2ACUJg2faYd-_Wr3NWoj_GtbW5Bje3G9+o595GyEhcBkbrg@mail.gmail.com>
In-Reply-To: <CALj2ACUJg2faYd-_Wr3NWoj_GtbW5Bje3G9+o595GyEhcBkbrg@mail.gmail.com>
From: shveta malik <shveta.malik@gmail.com>
Date: Tue, 3 Sep 2024 15:01:06 +0530
Message-ID: <CAJpy0uC8Dg-0JS3NRUwVUemgz5Ar2v3_EQQFXyAigWSEQ8U47Q@mail.gmail.com>
Subject: Re: Introduce XID age and inactive timeout based replication slot invalidation
To: Bharath Rupireddy <bharath.rupireddyforpostgres@gmail.com>
Cc: Peter Smith <smithpb2250@gmail.com>, Amit Kapila <amit.kapila16@gmail.com>, 
	Ajin Cherian <itsajin@gmail.com>, Bertrand Drouvot <bertranddrouvot.pg@gmail.com>, 
	Masahiko Sawada <sawada.mshk@gmail.com>, Nathan Bossart <nathandbossart@gmail.com>, 
	PostgreSQL Hackers <pgsql-hackers@lists.postgresql.org>, shveta malik <shveta.malik@gmail.com>
Content-Type: text/plain; charset="UTF-8"
Content-Transfer-Encoding: quoted-printable
Archived-At: <https://www.postgresql.org/message-id/CAJpy0uC8Dg-0JS3NRUwVUemgz5Ar2v3_EQQFXyAigWSEQ8U47Q%40mail.gmail.com>
Precedence: bulk

On Sat, Aug 31, 2024 at 1:45=E2=80=AFPM Bharath Rupireddy
<bharath.rupireddyforpostgres@gmail.com> wrote:
>
> Hi,
>
>
> Please find the attached v44 patch with the above changes. I will
> include the 0002 xid_age based invalidation patch later.
>

Thanks for the patch Bharath. My review and testing is WIP, but please
find few comments and queries:

1)
I see that ReplicationSlotAlter() will error out if the slot is
invalidated due to timeout. I have not tested it myself, but do you
know if  slot-alter errors out for other invalidation causes as well?
Just wanted to confirm that the behaviour is consistent for all
invalidation causes.

2)
When a slot is invalidated, and we try to use that slot, it gives this msg:

ERROR:  can no longer get changes from replication slot "mysubnew1_2"
DETAIL:  The slot became invalid because it was inactive since
2024-09-03 14:23:34.094067+05:30, which is more than 600 seconds ago.
HINT:  You might need to increase "replication_slot_inactive_timeout.".

Isn't HINT misleading? Even if we increase it now, the slot can not be
reused again.


3)
When the slot is invalidated, the' inactive_since' still keeps on
changing when there is a subscriber trying to start replication
continuously. I think ReplicationSlotAcquire() keeps on failing and
thus Release keeps on setting it again and again. Shouldn't we stop
setting/chnaging  'inactive_since' once the slot is invalidated
already, otherwise it will be misleading.

postgres=3D# select failover,synced,inactive_since,invalidation_reason
from pg_replication_slots;

 failover | synced |          inactive_since          | invalidation_reason
----------+--------+----------------------------------+--------------------=
-
 t        | f      | 2024-09-03 14:23:.. | inactive_timeout

after sometime:
 failover | synced |          inactive_since          | invalidation_reason
----------+--------+----------------------------------+--------------------=
-
 t        | f      | 2024-09-03 14:26:..| inactive_timeout


4)
src/sgml/config.sgml:

4a)
+ A value of zero (which is default) disables the timeout mechanism.

Better will be:
A value of zero (which is default) disables the inactive timeout
invalidation mechanism .
or
A value of zero (which is default) disables the slot invalidation due
to the inactive timeout mechanism.

i.e. rephrase to indicate that invalidation is disabled.

4b)
'synced' and inactive_since should point to pg_replication_slots:

example:
<link linkend=3D"view-pg-replication-slots">pg_replication_slots</link>.<st=
ructfield>synced</structfield>

5)
src/sgml/system-views.sgml:
+ ..the slot has been inactive for longer than the duration specified
by replication_slot_inactive_timeout parameter.

Better to have:
..the slot has been inactive for a time longer than the duration
specified by the replication_slot_inactive_timeout parameter.

thanks
Shveta