[jira] [Created] (IGNITE-22977) Reduce latency for txn preparing phase

["Alexey Scherbakov (Jira)" <ji...@apache.org>]

Alexey Scherbakov created IGNITE-22977:
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             Summary: Reduce latency for txn preparing phase
                 Key: IGNITE-22977
                 URL: https://issues.apache.org/jira/browse/IGNITE-22977
             Project: Ignite
          Issue Type: Improvement
    Affects Versions: 3.0
            Reporter: Alexey Scherbakov


Tx mapping phase has some deficiencies, discovered during tracing.
 # HybridClockImpl uses currentTimeMillis on each update. This call is heavy, better use FastTimestamps with 1 millisecond resolution.

 # CompletableFuture has unexpected latency issues:

 ## onTimeout add 4-5 us of latency

 ## chaining adds 0.5-1 us of latency. instead of using 
CompletableFuture.completedFuture(val).handle(closure) better to use if (fut.isDone()) closure();

 # Metadata validation {{{}validateTableExistence{}}}, {{{}validateSchemaMatch{}}}, {{{}waitForSchemasBeforeReading{}}}should wait only once.

 # Number of shared memory access (like updating some counter) should be reduced. For example tx counting should be only during index rebuild.

 # BinaryRow generation is 2x slower than BinaryObject in AI2: 5us vs 10us (known issue, just for clarity)

 # Thread switching brings a lot of latency (known issue, just for clarity). Can try green threads pool to mitigate this (requires java 21).

 # RAFT command is completed always in partitions thread pool

 # Number of {{clockService.now()}} calls should be reduced.

 # Each tx lock cost 2us. Might be improved to 1us.

 # Lease checking adds waiter even if not necessary.

 # Row id generation uses randomUUID which is heavy.



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