On Fri, Apr 27, 2012 at 1:51 AM, Josh Berkus wrote:
1. Out of 700 columns, columns 301+ are all Null, so we map them away.
2. User updates column 688 to non-null
3. Suddenly we have a MUCH larger row which will no longer fit on the page.
Note that this is only actually 48 bytes more in the null bitmap in
this scenario. That's part of Tom's point that the null bitmap is so
dense that you have to be talking about some pretty huge number of
columns before the size savings are noticeable. Saving 48 bytes is
nothing to sneeze at but it's hardly an impractical update to handle.

--
greg

Search Discussions

Discussion Posts

Previous

Follow ups

Related Discussions

Discussion Navigation
viewthread | post
posts ‹ prev | 14 of 28 | next ›
Discussion Overview
grouppgsql-hackers @
categoriespostgresql
postedApr 17, '12 at 4:23p
activeAug 10, '12 at 12:06a
posts28
users8
websitepostgresql.org...
irc#postgresql

People

Translate

site design / logo © 2021 Grokbase