This patch eliminates duplicate strings that come from the 'path' field of
java.io.File objects created by FileSegmentManagedBuffer. That is, we want
to avoid the situation when multiple File instances for the same pathname
"foo/bar" are created, each with a separate copy of the "foo/bar" String
instance. In some scenarios such duplicate strings may waste a lot of memory
(~ 10% of the heap). To avoid that, we intern the pathname with
String.intern(), and before that we make sure that it's in a normalized
form (contains no "//", "///" etc.) Otherwise, the code in java.io.File
would normalize it later, creating a new "foo/bar" String copy.
Unfortunately, the normalization code that java.io.File uses internally
is in the package-private class java.io.FileSystem, so we cannot call it
here directly.
## What changes were proposed in this pull request?
Added code to ExternalShuffleBlockResolver.getFile(), that normalizes and then interns the pathname string before passing it to the File() constructor.
## How was this patch tested?
Added unit test
Author: Misha Dmitriev <misha@cloudera.com>
Closes#21456 from countmdm/misha/spark-24356.
de4feae3cd