| From: | Heikki Linnakangas <hlinnaka(at)iki(dot)fi> |
|---|---|
| To: | Andrey Lepikhov <a(dot)lepikhov(at)postgrespro(dot)ru>, David Steele <david(at)pgmasters(dot)net>, a(dot)lubennikova(at)postgrespro(dot)ru |
| Cc: | Michael Paquier <michael(at)paquier(dot)xyz>, Dmitry Dolgov <9erthalion6(at)gmail(dot)com>, PostgreSQL-development <pgsql-hackers(at)postgresql(dot)org> |
| Subject: | Re: Reduce amount of WAL generated by CREATE INDEX for gist, gin and sp-gist |
| Date: | 2019-03-26 10:59:24 |
| Message-ID: | 43c42b20-c940-6dc1-cab1-caf722fdf403@iki.fi |
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| Lists: | pgsql-hackers |
On 26/03/2019 11:29, Andrey Lepikhov wrote:
> On 25/03/2019 15:21, Heikki Linnakangas wrote:
>> Hmm. When do we create all-zero pages during index build? That seems
>> pretty surprising.
>
> GIST uses buffered pages. During GIST build it is possible (very rarely)
> what no one index tuple was written to the block page before new block
> was allocated. And the page has become an all-zero page.
> You can't have problems in the current GIST code, because it writes into
> the WAL only changed pages.
Looking at the code, I don't see how that could happen. The only place
where the GiST index file is extended is in gistNewBuffer(), and all
callers of that initialize the page immediately after the call. What am
I missing?
- Heikki
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