Patrick McFadin created CASSANDRA-21660:
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Summary: 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
Reporter: Patrick McFadin
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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