| From: | Jim Nasby <Jim(dot)Nasby(at)BlueTreble(dot)com> |
|---|---|
| To: | Bruce Momjian <bruce(at)momjian(dot)us>, Alvaro Herrera <alvherre(at)2ndquadrant(dot)com> |
| Cc: | Simon Riggs <simon(dot)riggs(at)2ndquadrant(dot)com>, Andres Freund <andres(at)anarazel(dot)de>, Pavan Deolasee <pavan(dot)deolasee(at)gmail(dot)com>, Greg Stark <stark(at)mit(dot)edu>, Simon Riggs <simon(at)2ndquadrant(dot)com>, PostgreSQL-development <pgsql-hackers(at)postgresql(dot)org>, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>, Michael Paquier <michael(dot)paquier(at)gmail(dot)com>, Jeff Janes <jeff(dot)janes(at)gmail(dot)com>, Amit Kapila <amit(dot)kapila16(at)gmail(dot)com>, Peter Eisentraut <peter_e(at)gmx(dot)net>, Robert Haas <robertmhaas(at)gmail(dot)com> |
| Subject: | Re: Turning off HOT/Cleanup sometimes |
| Date: | 2015-04-21 20:45:11 |
| Message-ID: | 5536B6D7.8030904@BlueTreble.com |
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| Lists: | pgsql-hackers |
On 4/21/15 10:04 AM, Bruce Momjian wrote:
> One thing to consider is how we handle pruning of index scans that hit
> multiple heap pages. Do we still write X% of the pages in the table, or
> %X of the heap pages we actually access via SELECT? With the
> write-then-skip approach, we would do X% of the pages we access, while
> with the first-X% approach, we would probably prune all of them as we
> would not be accessing most of the table. I don't think we can do the
> first first-X% of pages and have the percentage based on the number of
> pages accessed as we have no way to know how many heap pages we will
> access from the index.
This comment made me wonder... has anyone considered handing the pruning
work off to a bgworker, at least for SELECTs? That means the selects
themselves wouldn't be burdened by the actual prune work, only in
notifying the bgworker. While that's not going to be free, presumably
it's a lot cheaper...
--
Jim Nasby, Data Architect, Blue Treble Consulting
Data in Trouble? Get it in Treble! http://BlueTreble.com
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