| From: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
|---|---|
| To: | Andres Freund <andres(at)anarazel(dot)de> |
| Cc: | John Naylor <jcnaylor(at)gmail(dot)com>, pgsql-hackers(at)postgresql(dot)org |
| Subject: | Re: reducing the footprint of ScanKeyword (was Re: Large writable variables) |
| Date: | 2018-12-22 18:28:35 |
| Message-ID: | 1645.1545503315@sss.pgh.pa.us |
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| Lists: | pgsql-hackers |
Andres Freund <andres(at)anarazel(dot)de> writes:
> On 2018-12-22 12:20:00 -0500, Tom Lane wrote:
>> I like that idea a *lot*, actually, because it offers the opportunity
>> to decouple this mechanism from all assumptions about what the
>> auxiliary data for a keyword is.
> OTOH, it doubles or triples the number of cachelines accessed when
> encountering a keyword.
Compared to what? The current situation in that regard is a mess.
Also, AFAICS this proposal involves the least amount of data touched
during the lookup phase of anything we've discussed, so I do not even
accept that your criticism is correct. One extra cacheline fetch
to get the aux data for a particular keyword after the search is not
going to tip the scales away from this being a win.
regards, tom lane
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