HDDS-14400. Avoid collecting keys in memory during parallel OM table processing

[navinko]

What changes were proposed in this pull request?

Avoid collecting keys in memory during parallel OM table processing.

Please describe your PR in detail:

• The new implementation keeps the iterator thread pool but removes the value-executor pool and in-memory batching.
• Each table iterator is now owned by a single worker thread and scans only its assigned key range.
• Each table iterator now runs on single thread and validated it, works as it is with ByteArrayCode .
• There will be another PR for replacing ByteArrayCodec with CodecBufferCodec under ParallelTableOperation.
  https://issues.apache.org/jira/browse/HDDS-14155
• Added unit test case for validating new flow .
• Fixed findbugs comments.

What is the link to the Apache JIRA

https://issues.apache.org/jira/browse/HDDS-14400

How was this patch tested?

CI:
https://github.com/navinko/ozone/actions/runs/20884674236
Validated with junit test and tested the flow by populating data to fileTable and validated the parallel processing for individual table in debug mode and normal.
bash-5.1$ ozone debug ldb --db=/data/metadata/om.db scan --column_family=fileTable --count
23916

Recon log

 Run mode with 21627 key uploaded to fileTable followed by reprocessing.

2026-01-10T15:42:37.870472510Z 2026-01-10 15:42:37,870 [ReconTaskThread-0] INFO tasks.ReconTaskControllerImpl: Task OmTableInsightTask started execution on thread ReconTaskThread-0
2026-01-10T15:42:37.870724094Z 2026-01-10 15:42:37,870 [ReconTaskThread-0] INFO tasks.OmTableInsightTask: OmTableInsightTask: Starting reprocess
2026-01-10T15:42:37.878627094Z 2026-01-10 15:42:37,878 [ReconTaskThread-0] INFO tasks.OmTableInsightTask: OmTableInsightTask: Processing table dTokenTable sequentially (non-String keys)
2026-01-10T15:42:37.888022094Z 2026-01-10 15:42:37,887 [ReconTaskThread-0] INFO util.ParallelTableIteratorOperation: OmTableInsightTask: Parallel iteration completed - Total keys processed: 2
2026-01-10T15:42:37.888184677Z 2026-01-10 15:42:37,888 [ReconTaskThread-0] INFO tasks.OmTableInsightTask: OmTableInsightTask: Processing table s3SecretTable sequentially (non-String keys)
2026-01-10T15:42:37.899993135Z 2026-01-10 15:42:37,899 [ReconTaskThread-0] INFO util.ParallelTableIteratorOperation: OmTableInsightTask: Parallel iteration completed - Total keys processed: 3
2026-01-10T15:42:37.944590219Z 2026-01-10 15:42:37,944 [ReconTaskThread-0] INFO util.ParallelTableIteratorOperation: OmTableInsightTask: Parallel iteration completed - Total keys processed: 21627
2026-01-10T15:42:37.947238802Z 2026-01-10 15:42:37,947 [ReconTaskThread-0] INFO tasks.OmTableInsightTask: OmTableInsightTask: Reprocess completed in 76 ms
2026-01-10T15:42:37.947249094Z 2026-01-10 15:42:37,947 [ReconTaskThread-0] INFO tasks.ReconTaskControllerImpl: Task OmTableInsightTask completed execution

[navinko]

Hi @swamirishi,
As suggested created a new PR - Avoid collecting keys in memory during parallel OM table processing #9624
Kindly review .

[jojochuang]

@rnblough