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Posted to commits@cassandra.apache.org by "Dmitry Konstantinov (Jira)" <ji...@apache.org> on 2025/11/20 22:32:00 UTC
[jira] [Commented] (CASSANDRA-20465) Reduce runtime overhead of org.apache.cassandra.schema.TableMetadataRef#get usage
[ https://issues.apache.org/jira/browse/CASSANDRA-20465?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=18039714#comment-18039714 ]
Dmitry Konstantinov commented on CASSANDRA-20465:
-------------------------------------------------
I've submitted a rebased and updated version with addressed review comments.
{quote}
yeah I think we could introduce special versions of those methods for this use case, but otoh, with the rest of the improvements in this PR I doubt they'll be necessary?
{quote}
Let me measure it and if it is still visible then I'll probably create another ticket for the change to not make the current change set too big.
> 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, 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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