Re: Performance Improvement by reducing WAL for Update Operation

On Thu, Jan 30, 2014 at 12:23 PM, Amit Kapila <amit(dot)kapila16(at)gmail(dot)com> wrote:
> On Wed, Jan 29, 2014 at 8:13 PM, Heikki Linnakangas
> <hlinnakangas(at)vmware(dot)com> wrote:
>
> Few observations in patch (back-to-pglz-like-delta-encoding-1):
>
> 1.
> +#define pgrb_hash_unroll(_p, hindex) \
> + hindex = hindex ^ ((_p)[0] << 8)
>
> shouldn't it shift by 6 rather than by 8.
>
> 2.
> + if (bp - bstart >= result_max)
> + return false;
>
> I think for nothing or lesser match case it will traverse whole tuple.
> Can we optimize such that if there is no match till 75%, we can bail out.
> Ideally, I think if we don't find any match in first 50 to 60%, we should
> come out.
>
> 3. pg_rbcompress.h is missing.
>
> I am still working on patch back-to-pglz-like-delta-encoding-1 to see if
> it works well for all cases, but thought of sharing what I have done till
> now to you.
>
> After basic verification of back-to-pglz-like-delta-encoding-1, I will
> take the data with both the patches and report the same.

Apart from above, the only other thing which I found problematic is
below code in find match

+ while (*ip == *hp && thislen < maxlen)
+ thislen++;

It should be
while (*ip++ == *hp++ && thislen < maxlen)

Please confirm.

With Regards,
Amit Kapila.
EnterpriseDB: http://www.enterprisedb.com