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https://issues.apache.org/jira/browse/CASSANDRA-11206?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15198608#comment-15198608
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Stefania commented on CASSANDRA-11206:
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bq. My understanding of
{{UnfilteredRowIteratorWithLowerBound#getPartitionIndexLowerBound}} is, that it
uses the IndexInfo objects that are already in the key-cache and will go to
disk if there is a key-cache miss.
Yes. Except previously it had to do this anyway because of the partition
deletion, whereas now the partition deletion will be available but not the full
IndexInfo objects.
bq. We could (in theory) add stuff to the partition summary or change the
serialized index - but unfortunately not in 3.x.
I think it's reasonable to wait until the new major version to improve on the
optimization of CASSANDRA-8180. So I'm happy with this compromise. Shall we
open a ticket for this?
> Support large partitions on the 3.0 sstable format
> --------------------------------------------------
>
> Key: CASSANDRA-11206
> URL: https://issues.apache.org/jira/browse/CASSANDRA-11206
> Project: Cassandra
> Issue Type: Improvement
> Reporter: Jonathan Ellis
> Assignee: Robert Stupp
> Fix For: 3.x
>
>
> Cassandra saves a sample of IndexInfo objects that store the offset within
> each partition of every 64KB (by default) range of rows. To find a row, we
> binary search this sample, then scan the partition of the appropriate range.
> The problem is that this scales poorly as partitions grow: on a cache miss,
> we deserialize the entire set of IndexInfo, which both creates a lot of GC
> overhead (as noted in CASSANDRA-9754) but is also non-negligible i/o activity
> (relative to reading a single 64KB row range) as partitions get truly large.
> We introduced an "offset map" in CASSANDRA-10314 that allows us to perform
> the IndexInfo bsearch while only deserializing IndexInfo that we need to
> compare against, i.e. log(N) deserializations.
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