Jon Meredith commented on CASSANDRA-14832:

PR https://github.com/apache/cassandra/pull/288

> Other threads can take all newly allocated BufferPool chunks before original 
> and cause reallocation
> ---------------------------------------------------------------------------------------------------
>                 Key: CASSANDRA-14832
>                 URL: https://issues.apache.org/jira/browse/CASSANDRA-14832
>             Project: Cassandra
>          Issue Type: Improvement
>          Components: Core
>            Reporter: Jon Meredith
>            Priority: Minor
> When BufferPool does not have any free Chunks to satisfy a request, the 
> calling thread allocates a new large block of memory which it breaks up into 
> chunks and adds to the free chunks queue, then pulls from the queue to 
> satisfy it's own allocation.
> If enough other threads request chunks it is possible for the queue to be 
> exhausted before the original allocating thread is able to pull of it's own 
> allocation, causing the original allocator to loop and attempt to allocate 
> more memory.  This is unfair to the original caller and may cause it to block 
> on a system call to allocate more memory.
> Instead of the current behavior, allocateMoreChunks could hold back one of 
> the chunks and return it to the caller instead so that it will at most call 
> allocate once.

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