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Date: Sat, 19 Mar 2016 15:44:33 +0000 (UTC)
From: "Jack Krupansky (JIRA)" <jira@apache.org>
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Subject: [jira] [Commented] (CASSANDRA-11383) SASI index build leads to
 massive OOM
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    [ https://issues.apache.org/jira/browse/CASSANDRA-11383?page=3Dcom.atla=
ssian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=
=3D15202816#comment-15202816 ]=20

Jack Krupansky commented on CASSANDRA-11383:
--------------------------------------------

The terminology is a bit confusing here - everybody understands what a spar=
se matrix is, but exactly what constitutes sparseness in a column is very u=
nclear. What is clear is that  the cardinality (number of distinct values) =
is low for that int field. A naive person (okay... me) would have thought t=
hat sparse data meant few distinct values, which is what the int field is (=
36 distinct values.)

I decided to check the doc to see what it says about SPARSE, but discovered=
 that the doc doesn't exist yet in the main Cassandra doc - I sent a messag=
e to docs@datastax.com about that. So I went back to the orginal, pre-integ=
ration doc (https://github.com/xedin/sasi) and see that there is separate, =
non-integrated doc for SASI in the Cassandra source tree - https://github.c=
om/apache/cassandra/blob/trunk/doc/SASI.md, which makes clear that "SPARSE,=
 which is meant to improve performance of querying large, dense number rang=
es like timestamps for data inserted every millisecond." Oops... SPARSE=3Dd=
ense, but in any case SPARSE is designed for high cardinality of distinct v=
alues, which the int field is clearly not.

I would argue that SASI should give a strongly-worded warning if the column=
 data for a SPARSE index has low cardinality - low number of distinct colum=
n values and high number of index values per column value.

> SASI index build leads to massive OOM
> -------------------------------------
>
>                 Key: CASSANDRA-11383
>                 URL: https://issues.apache.org/jira/browse/CASSANDRA-1138=
3
>             Project: Cassandra
>          Issue Type: Bug
>          Components: CQL
>         Environment: C* 3.4
>            Reporter: DOAN DuyHai
>         Attachments: CASSANDRA-11383.patch, new_system_log_CMS_8GB_OOM.lo=
g, system.log_sasi_build_oom
>
>
> 13 bare metal machines
> - 6 cores CPU (12 HT)
> - 64Gb RAM
> - 4 SSD in RAID0
>  JVM settings:
> - G1 GC
> - Xms32G, Xmx32G
> Data set:
>  - =E2=89=88 100Gb/per node
>  - 1.3 Tb cluster-wide
>  - =E2=89=88 20Gb for all SASI indices
> C* settings:
> - concurrent_compactors: 1
> - compaction_throughput_mb_per_sec: 256
> - memtable_heap_space_in_mb: 2048
> - memtable_offheap_space_in_mb: 2048
> I created 9 SASI indices
>  - 8 indices with text field, NonTokenizingAnalyser,  PREFIX mode, case-i=
nsensitive
>  - 1 index with numeric field, SPARSE mode
>  After a while, the nodes just gone OOM.
>  I attach log files. You can see a lot of GC happening while index segmen=
ts are flush to disk. At some point the node OOM ...
> /cc [~xedin]


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