| From: | Robert Haas <robertmhaas(at)gmail(dot)com> |
|---|---|
| To: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
| Cc: | Stephen Frost <sfrost(at)snowman(dot)net>, Amit Kapila <amit(dot)kapila16(at)gmail(dot)com>, Jesper Pedersen <jesper(dot)pedersen(at)redhat(dot)com>, Jeff Janes <jeff(dot)janes(at)gmail(dot)com>, pgsql-hackers <pgsql-hackers(at)postgresql(dot)org> |
| Subject: | Re: Write Ahead Logging for Hash Indexes |
| Date: | 2017-03-15 15:12:37 |
| Message-ID: | CA+TgmoZtGKo+UTqHN3ySzT5LuynzGAdFQ6FMqKfPXAA1r_PO1A@mail.gmail.com |
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| Lists: | pgsql-hackers |
On Wed, Mar 15, 2017 at 11:02 AM, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
> Robert Haas <robertmhaas(at)gmail(dot)com> writes:
>> That theory seems inconsistent with how mdextend() works. My
>> understanding is that we zero-fill the new blocks before populating
>> them with actual data precisely to avoid running out of disk space due
>> to deferred allocation at the OS level. If we don't care about
>> failures due to deferred allocation at the OS level, we can rip that
>> logic out and improve the performance of relation extension
>> considerably.
>
> See my reply to Stephen. The fact that this fails to guarantee no
> ENOSPC on COW filesystems doesn't mean that it's not worth doing on
> other filesystems. We're reducing the risk, not eliminating it,
> but reducing risk is still a worthwhile activity.
Well, then it would presumably be worth reducing for hash indexes, too.
--
Robert Haas
EnterpriseDB: http://www.enterprisedb.com
The Enterprise PostgreSQL Company
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