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https://issues.apache.org/jira/browse/CASSANDRA-5357?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13864543#comment-13864543
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Jonathan Ellis commented on CASSANDRA-5357:
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bq. I think we could also do some intelligent sizing of the cache per-CF with
the metrics we keep, that would be relatively static (so impervious to churn).
I'm not sure what I was thinking here. (Maybe that we'd only need one cached
partition per CF which is nonsense.) We do need LRU or similar behavior at a
high level, just like we do with the row cache today.
The question is, how much of each partition do we cache? I think it's a lot
simpler if we decide we'll cache the same amount for each partition in a CF,
and not try to be clever and "extend" a cached partition when we query for more
later.
So how much do we cache? We can either
# Make the user configure it, which requires creating new CQL syntax, or
# Determine it automatically
Personally I'd lean towards (2):
# Track an EstimatedHistogram of LIMITs in qualifying queries
# Set the cells-to-cache per CF so that we maximize the queries we can satisfy
for a given cache size
# I think this also means we should go back to a separate cache per CF with its
own size limit -- if we have 1000 queries/s against CF X's cache, then we
shouldn't throw those away when a query against CF Y comes in where we expect
only 10/s
In the interest of shipping sooner than later though I'll take whatever we can
reasonably do for 2.1.0 and push the rest out to improve later. If we just
have a single "cache this many cells" parameter in cassandra.yaml that's still
better than people OOMing themselves with the classic row cache.
> Query cache
> -----------
>
> Key: CASSANDRA-5357
> URL: https://issues.apache.org/jira/browse/CASSANDRA-5357
> Project: Cassandra
> Issue Type: Bug
> Reporter: Jonathan Ellis
> Assignee: Marcus Eriksson
> Fix For: 2.1
>
>
> I think that most people expect the row cache to act like a query cache,
> because that's a reasonable model. Caching the entire partition is, in
> retrospect, not really reasonable, so it's not surprising that it catches
> people off guard, especially given the confusion we've inflicted on ourselves
> as to what a "row" constitutes.
> I propose replacing it with a true query cache.
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