Re: pglz performance

On Tue, Nov 26, 2019 at 08:17:13PM +0100, Peter Eisentraut wrote:
>On 2019-11-26 10:43, Tomas Vondra wrote:
>>In general, I think the results for both patches seem clearly a win, but
>>maybe patch 1 is  bit better, especially on the newer (xeon) CPU. So I'd
>>probably go with that one.
>
>Patch 1 is also the simpler patch, so it seems clearly preferable.
>

Yeah, although the difference is minimal. We could probably construct a
benchmark where #2 wins, but I think these queries are fairly realistic.
So I'd just go with #1.

Code-wise I think the patches are mostly fine, although the comments
might need some proof-reading.

1) I wasn't really sure what a "nibble" is, but maybe it's just me and
it's a well-known term.

2) First byte use lower -> First byte uses lower

3) nibble contain upper -> nibble contains upper

4) to preven possible uncertanity -> to prevent possible uncertainty

5) I think we should briefly explain why memmove would be incompatible
with pglz, it's not quite clear to me.

6) I'm pretty sure the comment in the 'while (off < len)' branch will be
badly mangled by pgindent.

7) The last change moving "copy" to the next line seems unnecessary.


regards

-- 
Tomas Vondra                  http://www.2ndQuadrant.com
PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services