Re: Re: patch submission: truncate trailing nulls from heap rows to reduce the size of the null bitmap [Review]

On 20 December 2012 14:56, Amit Kapila  wrote:

>> > 1. There is no performance change for cloumns that have all valid
>> > values(non- NULLs).

I don't see any tests (at all) that measure this.

I'm particularly interested in lower numbers of columns, so we can
show no regression for the common case.


>> > 2. There is a visible performance increase when number of columns
>> containing
>> > NULLS are more than > 60~70% in table have large number of columns.
>> >
>> > 3. There are visible space savings when number of columns containing
>> NULLS
>> > are more than > 60~70% in table have large number of columns.

Agreed.

I would call that quite disappointing though and was expecting better.
Are we sure the patch works and the tests are correct?

The lack of any space saving for lower % values is strange and
somewhat worrying. There should be a 36? byte saving for 300 null
columns in an 800 column table - how does that not show up at all?

-- Simon Riggs                   http://www.2ndQuadrant.com/PostgreSQL Development, 24x7 Support, Training & Services