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https://issues.apache.org/jira/browse/IGNITE-7812?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16429252#comment-16429252
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Joel Lang commented on IGNITE-7812:
-----------------------------------

I've found that this happens after page eviction begins for the cache. It seems 
to be related to file reads in PageMemoryImpl.acquirePage() as a result of the 
H2 query index being updated when new rows are received during rebalancing. The 
segment write lock is held during these read operations which dramatically 
slows down other operations. It was a crippling slowdown in my test case which 
was done on a development VM which uses a HDD, not a SSD. We would be looking 
at 1-2 days of rebalance time for a cache with 6 million entries and 2 indexes 
in t hat case.

Fortunately, it seems as if this has already been fixed for 2.5, the disk read 
happens after the segment write lock is released now: 
[PageMemoryImpl.java#L750|https://github.com/apache/ignite/blob/master/modules/core/src/main/java/org/apache/ignite/internal/processors/cache/persistence/pagemem/PageMemoryImpl.java#L750]

> Slow rebalancing in case of enabled persistence
> -----------------------------------------------
>
>                 Key: IGNITE-7812
>                 URL: https://issues.apache.org/jira/browse/IGNITE-7812
>             Project: Ignite
>          Issue Type: Task
>            Reporter: Alexey Goncharuk
>            Assignee: Pavel Kovalenko
>            Priority: Major
>
> A user reported that rebalancing take significantly larger amounts of time 
> when persistence is enabled even in LOG_ONLY mode.
> Need to investigate how the performance of rebalancing may be increased.
> Also, it would be great to estimate the benefit of file transfer for 
> rebalancing.



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