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From "Sylvain Lebresne (JIRA)" <>
Subject [jira] [Commented] (CASSANDRA-6492) Have server pick query page size by default
Date Thu, 16 Jul 2015 16:09:05 GMT


Sylvain Lebresne commented on CASSANDRA-6492:

bq. If we translate a byte-based page size into a row-based one using internal metrics, we
lose most of those advantages.

I don't understand, how is that different from your "Perhaps a good first step is to add support
for automatic page size selection"? What did you had in mind for that? Because the only idea
I had to do that from the internal metrics would be to use the metrics to get a estimated
average row size, pick some presumably hard-coded bytes size target for a page, and compute
the actual page size in rows from that. In which case, I'm saying that instead of hard-coding
that target and since we'll need a modification to the protocol anyway, let's allow the user
to provide that target. It's more flexible than just having the options of "a page size in
row" or "some default".

Or to put it another way, having the server pick a default is not the problem we're trying
to fix. The problem we're trying to fix is that to pick a proper page size, you currently
have to guess-estimate the average size of your rows, but we can do a better guess-estimation
server side and that's what we should provide here. Of course its still imperfect, but I think
we're in agreement that the no-guess-estimate solution is a lot more involved.

And one of the bonus of directly modifying the protocol to allow a page size target in bytes
(rather than only providing a default mode with hard-coded target server side) is that once
we do implement the more involved change-the-internals solution, we'll have no additional
use visible change to do, thing will just get auto-magically better and safer.

> Have server pick query page size by default
> -------------------------------------------
>                 Key: CASSANDRA-6492
>                 URL:
>             Project: Cassandra
>          Issue Type: New Feature
>          Components: API
>            Reporter: Jonathan Ellis
>            Assignee: Benjamin Lerer
>            Priority: Minor
> We're almost always going to do a better job picking a page size based on sstable stats,
than users will guesstimating.

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