[
https://issues.apache.org/jira/browse/CASSANDRA-21661?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
]
Patrick McFadin updated CASSANDRA-21661:
----------------------------------------
Resolution: Duplicate
Status: Resolved (was: Triage Needed)
New Jira superceeds this one
> Stop rebuilding a map of every table on each DistributedSchema construction
> ---------------------------------------------------------------------------
>
> Key: CASSANDRA-21661
> URL: https://issues.apache.org/jira/browse/CASSANDRA-21661
> Project: Apache Cassandra
> Issue Type: Improvement
> Components: Cluster/Schema
> Reporter: Patrick McFadin
> Assignee: Patrick McFadin
> Priority: Normal
> Time Spent: 20m
> Remaining Estimate: 0h
>
> h2. What
> DistributedSchema's constructor builds a flat
> ImmutableMap<TableId,TableMetadata> over every table in every keyspace, then
> validate() walks them again. It runs twice per DDL – once in AlterSchema,
> once via Transformer.build -> withLastModified. Keyspaces already maintains
> that mapping internally and already exposes getTableOrViewNullable(id), so it
> is a rebuild of data the constructor was just handed.
> h2. Change
> Delete keyspacesToTableMap and the field it populated; point the single
> reader at keyspaces.getTableOrViewNullable(id). Net -11/+1 lines, no API
> change.
> validate() is left alone deliberately: its allocation is per-keyspace, not
> per-table (the Preconditions.checkArgument calls bind Guava's 3-Object
> overload, not varargs). The after numbers confirm it – they do not move when
> the table count grows 8x.
> h2. Result
> Per withLastModified call:
> ||fixture||400 tables||3200 tables||growth||
> |before, 10 keyspaces|27,288 B|182,808 B|6.7x|
> |before, 1 keyspace|22,812 B|179,825 B|7.9x|
> |after, 10 keyspaces|2,032 B|2,032 B|1.0x|
> |after, 1 keyspace|401 B|376 B|0.9x|
> h2. One behavior not preserved
> ImmutableMap.Builder.build() threw on duplicate keys, implicitly asserting no
> two keyspaces share a TableId. Keyspaces' BTreeMap collapses such a duplicate
> silently, so that check is gone. Not restored here: Keyspaces had already
> collapsed it before DistributedSchema saw it, every other TCM lookup already
> went through the collapsed map, and a set-based check would reintroduce the
> allocation this removes. Right home is an O(1) guard in
> Keyspaces.withTablesViews. No existing test covers it. Recorded as a
> decision, not a silent loss.
> h2. Tests
> New DistributedSchemaScalingTest: 2 allocation assertions, 5 correctness
> guards including views reachable by their own id (the old map came from
> tablesAndViews(), so delegation must not narrow to base tables). Verified red
> without the fix. Regression: schema 28 suites/137 tests, tcm 13/55, 0
> failures. checkstyle clean.
--
This message was sent by Atlassian Jira
(v8.20.10#820010)
---------------------------------------------------------------------
To unsubscribe, e-mail: [email protected]
For additional commands, e-mail: [email protected]
