From: | Kyotaro Horiguchi <horikyota(dot)ntt(at)gmail(dot)com> |
---|---|
To: | tsunakawa(dot)takay(at)fujitsu(dot)com |
Cc: | amit(dot)kapila16(at)gmail(dot)com, andres(at)anarazel(dot)de, k(dot)jamison(at)fujitsu(dot)com, tgl(at)sss(dot)pgh(dot)pa(dot)us, thomas(dot)munro(at)gmail(dot)com, robertmhaas(at)gmail(dot)com, tomas(dot)vondra(at)2ndquadrant(dot)com, pgsql-hackers(at)postgresql(dot)org |
Subject: | Re: [Patch] Optimize dropping of relation buffers using dlist |
Date: | 2020-12-22 03:00:07 |
Message-ID: | 20201222.120007.256404360834912579.horikyota.ntt@gmail.com |
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Lists: | pgsql-hackers |
At Tue, 22 Dec 2020 02:48:22 +0000, "tsunakawa(dot)takay(at)fujitsu(dot)com" <tsunakawa(dot)takay(at)fujitsu(dot)com> wrote in
> From: Amit Kapila <amit(dot)kapila16(at)gmail(dot)com>
> > Why would all client backends wait for AccessExclusive lock on this
> > relation? Say, a client needs a buffer for some other relation and
> > that might evict this buffer after we release the lock on the
> > partition. In StrategyGetBuffer, it is important to either have a pin
> > on the buffer or the buffer header itself must be locked to avoid
> > getting picked as victim buffer. Am I missing something?
>
> Ouch, right. (The year-end business must be making me crazy...)
>
> So, there are two choices here:
>
> 1) The current patch.
> 2) Acquire the buffer header spinlock before releasing the buffer mapping lwlock, and eliminate the buffer tag comparison as follows:
>
> BufTableLookup();
> LockBufHdr();
> LWLockRelease();
> InvalidateBuffer();
>
> I think both are okay. If I must choose either, I kind of prefer 1), because LWLockRelease() could take longer time to wake up other processes waiting on the lwlock, which is not very good to do while holding a spinlock.
I like, as said before, the current patch.
regareds.
--
Kyotaro Horiguchi
NTT Open Source Software Center
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