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https://issues.apache.org/jira/browse/CASSANDRA-11383?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15216233#comment-15216233
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Jack Krupansky commented on CASSANDRA-11383:
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Thanks, [~jrwest] and [~doanduyhai]. I think I finally have the SASI
terminology down now - SPARSE modes means that the index is sparse (few index
entries per original column value) while the column data is dense (many
distinct values.) And that non-SPARSE (AKA PREFIX) mode, the default mode,
supports any cardinality of data, especially the low cardinality data that
SPARSE mode does not support.
Maybe that leaves one last question as to whether non-SPARSE (PREFIX) mode is
considered advisable/recommended for high cardinality column data, where SPARSE
mode is nominally a better choice. Maybe that is strictly a matter of whether
the prefix/LIKE feature is to be utilized - if so, than PREFIX mode is
required, but if not, SPARSE mode sounds like the better choice. But I don't
have a handle on the internal index structures to know if that's absolutely the
case - that a PREFIX index for SPARSE data would necessarily be larger and/or
slower than a SPARSE index for high cardinality data. I would hope so, but it
would be good to have that confirmed.
> Avoid index segment stitching in RAM which lead to OOM on big SSTable files
> ----------------------------------------------------------------------------
>
> Key: CASSANDRA-11383
> URL: https://issues.apache.org/jira/browse/CASSANDRA-11383
> Project: Cassandra
> Issue Type: Bug
> Components: CQL
> Environment: C* 3.4
> Reporter: DOAN DuyHai
> Assignee: Jordan West
> Labels: sasi
> Fix For: 3.5
>
> Attachments: CASSANDRA-11383.patch,
> SASI_Index_build_LCS_1G_Max_SSTable_Size_logs.tar.gz,
> new_system_log_CMS_8GB_OOM.log, 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:
> - ≈ 100Gb/per node
> - 1.3 Tb cluster-wide
> - ≈ 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-insensitive
> - 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 segments
> are flush to disk. At some point the node OOM ...
> /cc [~xedin]
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