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https://issues.apache.org/jira/browse/CASSANDRA-20465?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Dmitry Konstantinov updated CASSANDRA-20465:
--------------------------------------------
Status: Ready to Commit (was: Review In Progress)
> Reduce runtime overhead of org.apache.cassandra.schema.TableMetadataRef#get
> usage
> ----------------------------------------------------------------------------------
>
> Key: CASSANDRA-20465
> URL: https://issues.apache.org/jira/browse/CASSANDRA-20465
> Project: Apache Cassandra
> Issue Type: Improvement
> Components: Cluster/Schema, Transactional Cluster Metadata
> Reporter: Dmitry Konstantinov
> Assignee: Dmitry Konstantinov
> Priority: Normal
> Fix For: 5.x
>
> Attachments: 5.1_cpu.html, CASSANDRA-20465_ci_summary.htm,
> CASSANDRA-20465_results_details.tar.xz, image-2025-03-20-22-43-09-044.png,
> image-2025-03-20-22-46-34-571.png, image-2025-03-20-22-52-40-818.png,
> image-2025-03-20-22-53-25-001.png, image-2025-03-20-22-56-31-298.png,
> image-2025-03-20-22-58-00-837.png, image-2025-07-09-11-04-45-311.png,
> write_after.html, write_before.html
>
> Time Spent: 20m
> Remaining Estimate: 0h
>
> Before TCM changes org.apache.cassandra.schema.TableMetadataRef#get
> invocation was cheap (it just returned a field value), now it does a lookup
> from Schema every time with a search a BTree + nota very cheap check is it a
> system keyspace.
> Diff:
> !image-2025-03-20-22-43-09-044.png|width=300!
> We have several places in code which uses TableMetadataRef#get and assume a
> low cost for it.
> Currently we have about 0.93% of CPU spent for this operation in total. If we
> check percentage for (compaction + flush) threads - it is 5.4% and 9.4% for
> compaction only ( [^5.1_cpu.html] ).
> Not sure if it is easy to reduce overheads in TableMetadataRef#get itself but
> we also can avoid them in many cases by a small adjustment of a logic on an
> invoker side to avoid too frequent usage of TableMetadataRef#get:
> 1) org.apache.cassandra.db.ColumnFamilyStore#isRowCacheEnabled - by default
> row cache is fully disabled - probably it is better to check if it is enabled
> as a first condition:
> !image-2025-03-20-22-46-34-571.png|width=300!
> 2) org.apache.cassandra.db.memtable.TrieMemtable#getFlushSet - we can lookup
> metadata once at the beginning of getFlushSet logic
> !image-2025-03-20-22-52-40-818.png|width=300!
> !image-2025-03-20-22-53-25-001.png|width=300!
> 3) org.apache.cassandra.io.sstable.SSTableIdentityIterator.create - to think
> if we can retrieve TableMetadata at the beginning a compaction and use during
> it..
> !image-2025-03-20-22-56-31-298.png|width=300!
> 4) org.apache.cassandra.io.sstable.keycache.KeyCacheSupport.getCacheKey - to
> think if we can retrieve only needed id/indexName fields once (at leas t and
> id does not look like a dynamically changed parameter ..)
> !image-2025-03-20-22-58-00-837.png|width=300!
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