| From: | Rajeev rastogi <rajeev(dot)rastogi(at)huawei(dot)com> |
|---|---|
| To: | Joshua Yanovski <pythonesque(at)gmail(dot)com> |
| Cc: | "pgsql-hackers(at)postgresql(dot)org" <pgsql-hackers(at)postgresql(dot)org> |
| Subject: | Re: Proposal: COUNT(*) (and related) speedup |
| Date: | 2014-04-07 13:10:37 |
| Message-ID: | BF2827DCCE55594C8D7A8F7FFD3AB7713DDDF1C3@SZXEML508-MBX.china.huawei.com |
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| Lists: | pgsql-hackers |
On 04 April 2014 18:09, Joshua Yanovski Wrote:
> The counter would be updated only by VACUUM, which would perform the
> same computation performed by the COUNT operation but add it
> permanently to counter just before it set the visible_map bit to 1 (I
> am not certain whether this would require unusual changes to WAL
> replay or not).
I think there is one more disadvantages with this (or maybe I have missed something):
User may not use count(*) or may use just once after creating new kind of index proposed but VACUUM will have to keep performing operation equivalent to iterative count(*), which might degrade performance for VACUUM.
Thanks and Regards,
Kumar Rajeev Rastogi
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