Hello Csaba Ringhofer,

I'd like you to reexamine a change. Please visit

    http://gerrit.cloudera.org:8080/9576

to look at the new patch set (#2).

Change subject: IMPALA-6638: Reduce file handle cache lock contention
......................................................................

IMPALA-6638: Reduce file handle cache lock contention

FileHandleCache::OpenFileHandle() currently holds the
lock while opening a file handle. This lengthens the
duration holding the lock considerably, causing
contention when a lot of file handles are being
opened (i.e. when the cache is cold).

This changes FileHandleCache::OpenFileHandle() drops
the lock while opening the file handle, then
reacquires it to add the file handle to the cache.

When running a simple select on a table with 46801
Parquet files, this fixes a small performance overhead
for the cold cache case compared to having the
cache off. All results are averaged over 5 runs:

File handle cache off: 7.19s
File handle cache cold (no patch): 7.92s
File handle cache cold (with patch): 7.20s

When running a select that accesses and aggregates
4 columns from the same Parquet table (thus requiring
more scan ranges for the same file), the fix reduces
contention, particularly for the case with 8 IO threads
per disk:

1 IO thread per disk:
Without patch: 9.59s
With patch: 8.11s

8 IO threads per disk:
Without patch: 14.2s
With patch: 8.17s

The patch has no impact on the performance when the
cache is hot.

Change-Id: I4c695b21ca556e9c73c703c0c891e64939271c8d
---
M be/src/runtime/io/handle-cache.inline.h
1 file changed, 30 insertions(+), 24 deletions(-)


  git pull ssh://gerrit.cloudera.org:29418/Impala-ASF refs/changes/76/9576/2
--
To view, visit http://gerrit.cloudera.org:8080/9576
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Gerrit-Project: Impala-ASF
Gerrit-Branch: master
Gerrit-MessageType: newpatchset
Gerrit-Change-Id: I4c695b21ca556e9c73c703c0c891e64939271c8d
Gerrit-Change-Number: 9576
Gerrit-PatchSet: 2
Gerrit-Owner: Joe McDonnell <joemcdonn...@cloudera.com>
Gerrit-Reviewer: Csaba Ringhofer <csringho...@cloudera.com>
Gerrit-Reviewer: Joe McDonnell <joemcdonn...@cloudera.com>

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