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https://issues.apache.org/jira/browse/HADOOP-18291?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17716841#comment-17716841
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Steve Loughran commented on HADOOP-18291:
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something in the storecontext should allocate/release blocks, set a limit etc.
interesting q. here: can one thread use up space that another has in cache? and
if so, how to stop things breaking dramatically?
you'd maybe want a block cache - readers would lock their block before a read;
unlock after. Use an LRU policy for recycling blocks, with unbuffer/close
releasing all blocks of a caller.
or, if it is caller based, use read fully plan to scope release -you don't want
to free any blocks in a read range if they are present, do you?
Until this is in, the disk block cache can't be considered something you'd use
in production. memory one is a different story
> SingleFilePerBlockCache does not have a limit
> ---------------------------------------------
>
> Key: HADOOP-18291
> URL: https://issues.apache.org/jira/browse/HADOOP-18291
> Project: Hadoop Common
> Issue Type: Sub-task
> Affects Versions: 3.4.0
> Reporter: Ahmar Suhail
> Priority: Major
>
> Currently there is no limit on the size of disk cache. This means we could
> have a large number of files on files, especially for access patterns that
> are very random and do not always read the block fully.
>
> eg:
> in.seek(5);
> in.read();
> in.seek(blockSize + 10) // block 0 gets saved to disk as it's not fully read
> in.read();
> in.seek(2 * blockSize + 10) // block 1 gets saved to disk
> .. and so on
>
> The in memory cache is bounded, and by default has a limit of 72MB (9
> blocks). When a block is fully read, and a seek is issued it's released
> [here|https://github.com/apache/hadoop/blob/feature-HADOOP-18028-s3a-prefetch/hadoop-tools/hadoop-aws/src/main/java/org/apache/hadoop/fs/s3a/read/S3CachingInputStream.java#L109].
> We can also delete the on disk file for the block here if it exists.
>
> Also maybe add an upper limit on disk space, and delete the file which stores
> data of the block furthest from the current block (similar to the in memory
> cache) when this limit is reached.
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