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From "Sylvain Lebresne (JIRA)" <>
Subject [jira] [Updated] (CASSANDRA-6446) Faster range tombstones on wide partitions
Date Tue, 07 Jan 2014 09:05:53 GMT


Sylvain Lebresne updated CASSANDRA-6446:

    Attachment: 6446-write-path-v3.txt

Attaching v3 versions that are basically rebased versions of v2. For the write path though,
v2 was checking the numbers of cells in the updated CF to decide which code path to use, but
with the new BTree implementation, there doesn't seem to be an easy way to get the number
of cells without iterating over all cells (which would defeat the purpose in that case). It's
probably possible to add such capability but I didn't dig that far. I simplified it by removing
the code path choice and only keeping the path that always iterate on ranges first, as it's
the one that won't crap itself when things grows. It might be slightly slower when there is
a small number of cells, but 1) it's not even all that clear that it's slower, 2) this is
only taken if there is 2ndary indexes to update and if the update applied has range tombstones
and 3) it avoids relying on some hardcoded and semi-randomly picked constant.

> Faster range tombstones on wide partitions
> ------------------------------------------
>                 Key: CASSANDRA-6446
>                 URL:
>             Project: Cassandra
>          Issue Type: Improvement
>          Components: Core
>            Reporter: Oleg Anastasyev
>            Assignee: Oleg Anastasyev
>             Fix For: 2.1
>         Attachments: 0001-6446-write-path-v2.txt, 0002-6446-Read-patch-v2.txt, 6446-Read-patch-v3.txt,
6446-write-path-v3.txt, RangeTombstonesReadOptimization.diff, RangeTombstonesWriteOptimization.diff
> Having wide CQL rows (~1M in single partition) and after deleting some of them, we found
inefficiencies in handling of range tombstones on both write and read paths.
> I attached 2 patches here, one for write path (RangeTombstonesWriteOptimization.diff)
and another on read (RangeTombstonesReadOptimization.diff).
> On write path, when you have some CQL rows deletions by primary key, each of deletion
is represented by range tombstone. On put of this tombstone to memtable the original code
takes all columns from memtable from partition and checks DeletionInfo.isDeleted by brute
for loop to decide, should this column stay in memtable or it was deleted by new tombstone.
Needless to say, more columns you have on partition the slower deletions you have heating
your CPU with brute range tombstones check. 
> The RangeTombstonesWriteOptimization.diff patch for partitions with more than 10000 columns
loops by tombstones instead and checks existance of columns for each of them. Also it copies
of whole memtable range tombstone list only if there are changes to be made there (original
code copies range tombstone list on every write).
> On read path, original code scans whole range tombstone list of a partition to match
sstable columns to their range tomstones. The RangeTombstonesReadOptimization.diff patch scans
only necessary range of tombstones, according to filter used for read.

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