| From: | Hannu Krosing <hannu(at)2ndQuadrant(dot)com> |
|---|---|
| To: | Andres Freund <andres(at)2ndquadrant(dot)com>, Hannu Krosing <hannu(at)2ndQuadrant(dot)com> |
| Cc: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>, Alvaro Herrera <alvherre(at)2ndquadrant(dot)com>, Greg Stark <stark(at)mit(dot)edu>, Pg Hackers <pgsql-hackers(at)postgresql(dot)org> |
| Subject: | Re: On partitioning |
| Date: | 2014-09-01 17:09:18 |
| Message-ID: | 5404A83E.7010405@2ndQuadrant.com |
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| Lists: | pgsql-hackers |
On 09/01/2014 05:52 PM, Andres Freund wrote:
> On 2014-08-29 20:12:16 +0200, Hannu Krosing wrote:
>> It would need to replace plain tid (pagenr, tupnr) with triple of (partid,
>> pagenr, tupnr).
>>
>> Cross-partition indexes are especially needed if we want to allow putting
>> UNIQUE constraints on non-partition-key columns.
> I actually don't think this is necessary. I'm pretty sure that you can
> build an efficient and correct version of unique constraints with
> several underlying indexes in different partitions each. The way
> exclusion constraints are implemented imo is a good guide.
>
> I personally think that implementing cross partition indexes has a low
> enough cost/benefit ratio that I doubt it's wise to tackle it anytime
> soon.
Also it has the downside of (possibly) making DROP PARTITION either
slow or wasting space until next VACUUM.
So if building composite unique indexes over multiple per-partition
indexes is doable, I would much prefer this.
Cheers
--
Hannu Krosing
PostgreSQL Consultant
Performance, Scalability and High Availability
2ndQuadrant Nordic OÜ
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