[infinispan-issues] [JBoss JIRA] (ISPN-12128) Remote read during state transfer should store entry in data container

[Dan Berindei (Jira)]

Dan Berindei created ISPN-12128:
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             Summary: Remote read during state transfer should store entry in data container
                 Key: ISPN-12128
                 URL: https://issues.redhat.com/browse/ISPN-12128
             Project: Infinispan
          Issue Type: Bug
          Components: Core, State Transfer
    Affects Versions: 11.0.1.Final
            Reporter: Dan Berindei
            Assignee: Dan Berindei
             Fix For: 12.0.0.Final


A cache with {{await-initial-transfer="false"}} will execute cache operations while it is receiving state, during rebalance phase {{READ_OLD_WRITE_ALL}}. State transfer can take a long time, and during that time, it is not a read owner for any segments, it is only a write owner for the segments it is receiving.

That means {{cache.get(k)}} will perform a remote lookup every time, even AFTER the node received entry {{k=v}} via transfer, as long as not all the nodes have confirmed the end of state transfer and the coordinator hasn't changed the rebalance phase to {{READ_ALL_WRITE_ALL}}.

The extra remote lookups can have a negative impact on application performance. Especially in a replicated cache, the application would expect reads to be very fast, and the repeated remote lookups would break that assumption.

In order to encourage {{await-initial-transfer="false"}} and eventually make it the default (ISPN-9112), we should limit the number of remote lookups performed by a node while is is a write-only owner of a key:
 * Remote reads should write the entry in the data container, the same way state transfer would (i.e. skipping the write if a write operation already changed the entry).
 * Reads should first look up the key in the local data container before going remotely. If the key exists locally, the value can be returned directly.



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