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From "Michael Kjellman (JIRA)" <j...@apache.org>
Subject [jira] [Comment Edited] (CASSANDRA-11206) Support large partitions on the 3.0 sstable format
Date Tue, 14 Jun 2016 02:14:58 GMT

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Michael Kjellman edited comment on CASSANDRA-11206 at 6/14/16 2:14 AM:
-----------------------------------------------------------------------

going thru the changes and have some questions :)

# RowIndexEntry$serializedSize used to return the size of the index for the entire row. As
the size of the IndexInfo elements are variable length I'm having trouble understanding how
the new/current implementation does this:
{code}
private static int serializedSize(DeletionTime deletionTime, long headerLength, int columnIndexCount)
    {
        return TypeSizes.sizeofUnsignedVInt(headerLength)
               + (int) DeletionTime.serializer.serializedSize(deletionTime)
               + TypeSizes.sizeofUnsignedVInt(columnIndexCount);
    }
{code}
# In the class level Javadoc for IndexInfo there is a lot of comment about serialization format
changes and even a comment "Serialization format changed in 3.0" yet I don't see any corresponding
changes in BigFormat$BigVersion
# I see a class named **Pre_C_11206_RowIndexEntry** in RowIndexEntryTest which has a lot of
the logic that used to be in RowIndexEntry. I don't see the logic outside of the test classes
though.


was (Author: mkjellman):
going thru the changes and have some questions :)

# RowIndexEntry$serializedSize used to return the size of the index for the entire row. As
the size of the IndexInfo elements are variable length I'm having trouble understanding how
the new/current implementation does this:
{code}
private static int serializedSize(DeletionTime deletionTime, long headerLength, int columnIndexCount)
    {
        return TypeSizes.sizeofUnsignedVInt(headerLength)
               + (int) DeletionTime.serializer.serializedSize(deletionTime)
               + TypeSizes.sizeofUnsignedVInt(columnIndexCount);
    }
{code}
# In the class level Javadoc for IndexInfo there is a lot of comment about serialization format
changes and even a comment "Serialization format changed in 3.0" yet I don't see any corresponding
changes in BigFormat$BigVersion

> 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
>          Components: Local Write-Read Paths
>            Reporter: Jonathan Ellis
>            Assignee: Robert Stupp
>              Labels: docs-impacting
>             Fix For: 3.6
>
>         Attachments: 11206-gc.png, trunk-gc.png
>
>
> 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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