Re: Optimizing pglz compressor

On 26.06.2013 16:37, Amit Kapila wrote:
> On Wednesday, June 26, 2013 2:15 AM Heikki Linnakangas wrote:
>> Can you also try the attached patch, please? It's the same as before,
>> but in this version, I didn't replace the prev and next pointers in
>> PGLZ_HistEntry struct with int16s. That avoids some table lookups, at
>> the expense of using more memory. It's closer to what we have without
>> the patch, so maybe that helps on your system.
>
> Yes it helped a lot on my system.

Ok, good. Strange, I did not expect such a big difference.

> There was minor problem in you patch, in one of experiments it crashed.
> Fix is not to access 0th history entry in function pglz_find_match(),
> modified patch is attached.

Thanks, good catch! I thought that a pointer to the 0th entry would
never make it into the prev/next fields, but it does. In fact, we never
store a NULL there anymore, a pointer to the 0th entry is now always
used to mean 'invalid'. I adjusted the patch to remove the NULL check,
and only check for the 0th entry.

Committed.

- Heikki