HIVE-30053: Support multi-threaded CachedStore prewarm - #6785
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September 16, 2026 21:53
…make size estimators concurrency safe
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@dengzhhu653 @deniskuzZ @saihemanth-cloudera would appreciate a review when you get a chance |
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| } | ||
| sharedCache.populateDatabasesInCache(databases); | ||
| LOG.info("Databases cache is now prewarmed. Now adding tables, partitions and statistics to the cache"); | ||
| int numberOfDatabasesCachedSoFar = 0; |
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Can you separate the prewarm from this class please, and create an interface to warm up the cache?
An interface for example:
interface MetaCachePreWarm extends AutoClosable, Configurable {
void initialize() throws MetaException;
void preWarm() throws MetaException;
....
}
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Done, prewarm now lives behind a MetaCachePreWarm interface @dengzhhu653
… specifiers, interrupt handling, visibility, line length)
…interface declarations, dead throws, unused import)
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we can move TablesPendingPrewarm into MetaCachePreWarm, and adds a new prioritizeTableForPrewarm(TableName ... tableName) method in MetaCachePreWarm. Rest looks goods to me |
…izeTableForPrewarm(TableName...) to MetaCachePreWarm per review
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Done @dengzhhu653 |
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dengzhhu653
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What changes were proposed in this pull request?
Adds metastore.cached.rawstore.prewarm.threads (default 1 = current single-threaded behavior). With N > 1, prewarm fans the per-table work (table + partitions + statistics + constraints) out to N worker threads, each with its own RawStore instance — mirroring how CacheUpdateMasterWork creates its private store. Workers drain the existing TablesPendingPrewarm stack, so each table is handed out exactly once and the prioritizeTableForPrewarm hot-table promotion keeps working. The memory-full early stop uses a shared flag with completePrewarm called exactly once, and the worker pool plus worker stores are torn down when prewarm finishes. The per-table logic is extracted verbatim into prewarmTable(); the single-threaded path runs through the same code.
Why are the changes needed?
Prewarm is single-threaded and latency-bound: one thread issues ~6-8 sequential queries per table. On our production deployment (Hive 4.2.0, 21k cached tables) prewarm takes ~10 minutes; with 8 threads it takes 195s vs 602s baseline (3.1x). Each worker uses one connection from the shared pool, so the config doc advises keeping the value below the pool size.
Does this PR introduce any user-facing change?
A new optional config, metastore.cached.rawstore.prewarm.threads, default 1 (no behavior change unless set).
How was this patch tested?
New unit test TestCachedStore#testPrewarmMultiThreaded runs a full prewarm with 4 threads against Derby and asserts every database, table and partition is cached. Full TestCachedStore suite passes (32/32). Benchmarked on a production deployment: 602s (1 thread) -> 195s (8 threads) for 21k tables.