| From: | Theodore Ts'o <tytso(at)mit(dot)edu> |
|---|---|
| To: | Jan Kara <jack(at)suse(dot)cz> |
| Cc: | Heikki Linnakangas <hlinnakangas(at)vmware(dot)com>, Andres Freund <andres(at)2ndQuadrant(dot)com>, Josh Berkus <josh(at)agliodbs(dot)com>, Hannu Krosing <hannu(at)2ndQuadrant(dot)com>, Trond Myklebust <trondmy(at)gmail(dot)com>, Kevin Grittner <kgrittn(at)ymail(dot)com>, "pgsql-hackers(at)postgresql(dot)org" <pgsql-hackers(at)postgresql(dot)org>, Dave Chinner <david(at)fromorbit(dot)com>, Joshua Drake <jd(at)commandprompt(dot)com>, Bottomley James <James(dot)Bottomley(at)HansenPartnership(dot)com>, Claudio Freire <klaussfreire(at)gmail(dot)com>, Robert Haas <robertmhaas(at)gmail(dot)com>, Mel Gorman <mgorman(at)suse(dot)de>, Jim Nasby <jim(at)nasby(dot)net>, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>, "lsf-pc(at)lists(dot)linux-foundation(dot)org" <lsf-pc(at)lists(dot)linux-foundation(dot)org>, Magnus Hagander <magnus(at)hagander(dot)net> |
| Subject: | Re: [Lsf-pc] Linux kernel impact on PostgreSQL performance |
| Date: | 2014-01-16 21:10:40 |
| Message-ID: | 20140116211040.GB12104@thunk.org |
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| Lists: | pgsql-hackers |
On Wed, Jan 15, 2014 at 10:35:44AM +0100, Jan Kara wrote:
> Filesystems could in theory provide facility like atomic write (at least up
> to a certain size say in MB range) but it's not so easy and when there are
> no strong usecases fs people are reluctant to make their code more complex
> unnecessarily. OTOH without widespread atomic write support I understand
> application developers have similar stance. So it's kind of chicken and egg
> problem. BTW, e.g. ext3/4 has quite a bit of the infrastructure in place
> due to its data=journal mode so if someone on the PostgreSQL side wanted to
> research on this, knitting some experimental ext4 patches should be doable.
For the record, a researcher (plus is PhD student) at HP Labs actually
implemented a prototype based on ext3 which created an atomic write
facility. It was good up to about 25% of the ext4 journal size (so, a
couple of MB), and it was use to research using persistent memory by
creating a persistent heap using standard in-memory data structures as
a replacement for using a database.
The results of their research work was that showed that ext3 plus
atomic write plus standard Java associative arrays beat using Sqllite.
It was a research prototype, so they didn't handle OOM kill
conditions, and they also didn't try benchmarking against a real
database instead of a toy database such as SqlLite, but if someone
wants to experiment with Atomic write, there are patches against ext3
that we can probably get from HP Labs.
- Ted
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