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https://issues.apache.org/jira/browse/CASSANDRA-21660?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Patrick McFadin updated CASSANDRA-21660:
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Component/s: Cluster/Schema
> Back Tables with a persistent map so schema changes do not copy the collection
> ------------------------------------------------------------------------------
>
> Key: CASSANDRA-21660
> URL: https://issues.apache.org/jira/browse/CASSANDRA-21660
> Project: Apache Cassandra
> Issue Type: Improvement
> Components: Cluster/Schema
> Reporter: Patrick McFadin
> Priority: Normal
> Time Spent: 10m
> Remaining Estimate: 0h
>
> h2. What
> Tables keep three ImmutableMaps and rebuild all of them on every mutation:
> with() is builder().add(this).add(table).build(), withSwapped() is
> without().with(). A single CREATE TABLE therefore copies every existing table
> into three fresh maps more than once, and Builder.add recomputes index
> metadata
> for every indexed table while doing so.
> CEP-21 converted the outer collection, Keyspaces, to a persistent BTreeMap.
> TCM holds schema at several epochs at once, so copy-on-write would copy the
> world
> per epoch. The collections nested inside a keyspace were not converted.
> h2. Change
> * Back the three maps with BTreeMap, so with/without/withSwapped update
> rather
> than copy.
> * Maintain index tables incrementally, keyed off IndexMetadata.name
> (provably the
> same key: indexTableName is base + '.' + index.name).
> * Builder keeps the duplicate-name rejection ImmutableMap.Builder.build()
> gave.
> h2. Result
> ||operation||400 before||3200 before||growth||400 after||3200 after||growth||
> |with|218,951 B|1,687,617 B|7.7x|5,728 B|5,920 B|1.0x|
> |withSwapped|425,824 B|3,349,656 B|7.9x|1,936 B|2,448 B|1.3x|
> |without|213,896 B|1,682,368 B|7.9x|928 B|1,200 B|1.3x|
> The residual 1.3x is the O(log n) a persistent map allocates per update.
> h2. REVIEWERS: requires a clean build
> Tables.indexTables() narrows from ImmutableMap to Map. That is binary
> incompatible, and ant's timestamp-based javac will not recompile callers whose
> source did not change. With a stale build/ you get a NoSuchMethodError inside
> SecondaryIndexManager.createIndex, which LocalLog.processPendingInternal
> catches
> and logs as "Could not process the entry" – leaving an index silently
> unregistered and surfacing later as an unrelated NPE. Run ant clean first. No
> source change can prevent this.
> h2. Tests
> New TablesScalingTest: 3 allocation assertions, 4 correctness guards
> (add/remove/
> replace semantics; iteration deterministic and agreeing with lookup by name
> and
> id). Regression on a clean build: schema 29 suites, tcm 13 suites, index 3
> suites
> /61 tests, 0 failures. Checkstyle and checkstyle-test clean.
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