On 20 December 2012 14:56, Amit Kapila <amit.kapila@huawei.com> 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
