From: | Amit Kapila <amit(dot)kapila16(at)gmail(dot)com> |
---|---|
To: | Thomas Munro <thomas(dot)munro(at)gmail(dot)com> |
Cc: | Robert Haas <robertmhaas(at)gmail(dot)com>, Andres Freund <andres(at)anarazel(dot)de>, Dilip Kumar <dilipbalaut(at)gmail(dot)com>, Dmitry Dolgov <9erthalion6(at)gmail(dot)com>, Kuntal Ghosh <kuntalghosh(dot)2007(at)gmail(dot)com>, Pg Hackers <pgsql-hackers(at)postgresql(dot)org> |
Subject: | Re: POC: Cleaning up orphaned files using undo logs |
Date: | 2019-07-24 09:32:45 |
Message-ID: | CAA4eK1JSk1kMhfUNePtsX6c9-RQKNMc-3HTiBDq8qkuBTfkSdw@mail.gmail.com |
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Lists: | pgsql-hackers |
On Wed, Jul 24, 2019 at 2:45 PM Amit Kapila <amit(dot)kapila16(at)gmail(dot)com> wrote:
>
> On Thu, Jul 18, 2019 at 5:10 PM Amit Kapila <amit(dot)kapila16(at)gmail(dot)com> wrote:
> >
> > On Mon, Jul 1, 2019 at 1:24 PM Thomas Munro <thomas(dot)munro(at)gmail(dot)com> wrote:
> > > Yep, that was completely wrong. Here's a new version.
>
> 10.
> I think UndoLogAllocate can leak allocation of slots. It first
> allocates the slot for a new log from the free pool in there is no
> existing slot/log, writes a WAL record and then at a later point of
> time it actually creates the required physical space in the log via
> extend_undo_log which also writes a separate WAL. Now, if there is a
> error between these two operations, then we will have a redundant slot
> allocated. What if there are repeated errors for similar thing from
> multiple backends after which system crashes. Now, after restart, we
> will allocate multiple slots for different lognos which don't have any
> actual (physical) logs. This might not be a big problem in practice
> because the chances of error between two operations are less, but
> can't we delay the WAL logging for allocation of a slot for a new log.
>
After sending this email, I was browsing the previous comments raised
by me for this patch and it seems this same point was raised
previously [1] as well and there were few additional questions related
to same (See point-1 in email [1].)
--
With Regards,
Amit Kapila.
EnterpriseDB: http://www.enterprisedb.com
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