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From "Impala Public Jenkins (Code Review)" <ger...@cloudera.org>
Subject [Impala-ASF-CR] IMPALA-6364: Bypass file handle cache for ineligible files
Date Fri, 05 Jan 2018 21:21:47 GMT
Impala Public Jenkins has submitted this change and it was merged. ( http://gerrit.cloudera.org:8080/8945
)

Change subject: IMPALA-6364: Bypass file handle cache for ineligible files
......................................................................

IMPALA-6364: Bypass file handle cache for ineligible files

Currently, all HdfsFileHandles are owned and constructed
by the file handle cache. When the file handle cache
is disabled or the file handle is not eligible for
caching, the HdfsFileHandle is stored exclusively in
ScanRange::exclusive_hdfs_fh_, but the HdfsFileHandle still
comes from the file handle cache. It is created via a call to
DiskIoMgr::GetCachedHdfsFileHandle() with 'require_new_handle'
set to true and destroyed via
DiskIoMgr::ReleaseCachedHdfsFileHandle() with 'destroy_handle'
set to true.

Recent testing has revealed that the lock on the file handle
cache is a bottleneck for workloads with many small remote
files. There is no benefit to storing these exclusive file
handles in the file handle cache, as they do not participate
in the caching.

This change introduces DiskIoMgr::GetExclusiveHdfsFileHandle()
and DiskIoMgr::ReleaseExclusiveHdfsFileHandle(). These are
equivalent to the Get/ReleaseCachedHdfsFileHandle() calls, except
they bypass the file handle cache and create/destroy the
file handle directly. ScanRange::Open()/Close(), which
populates and frees ScanRange::exclusive_hdfs_fh_, now uses
these new calls rather than accessing the file handle cache.
This avoids the locking entirely, solving the bottleneck.

To draw a distinction between the two codepaths, HdfsFileHandle
is now an abstract class with two subclasses:
 - CachedHdfsFileHandles cover all handles that live in file handle
   cache. Get/ReleaseCachedHdfsFileHandle() use this subclass.
 - ExclusiveHdfsFileHandles cover all cases where a file handle
   does not come from the cache. The new
   Get/ReleaseExclusiveHdfsFileHandle() use this subclass.

Separately, testing revealed that increasing the number of
partitions for the file handle cache also fixes the contention
problem. This changes the file handle cache to make the number
of partitions configurable via startup parameter
num_file_handle_cache_partitions. This allows mitigation of
future bottlenecks without a patch.

Change-Id: I4ab52b0884a909a4faeb6692f32d45878ea2838f
Reviewed-on: http://gerrit.cloudera.org:8080/8945
Reviewed-by: Joe McDonnell <joemcdonnell@cloudera.com>
Tested-by: Impala Public Jenkins
---
M be/src/runtime/io/disk-io-mgr.cc
M be/src/runtime/io/disk-io-mgr.h
M be/src/runtime/io/handle-cache.h
M be/src/runtime/io/handle-cache.inline.h
M be/src/runtime/io/request-ranges.h
M be/src/runtime/io/scan-range.cc
6 files changed, 138 insertions(+), 87 deletions(-)

Approvals:
  Joe McDonnell: Looks good to me, approved
  Impala Public Jenkins: Verified

-- 
To view, visit http://gerrit.cloudera.org:8080/8945
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Gerrit-Project: Impala-ASF
Gerrit-Branch: master
Gerrit-MessageType: merged
Gerrit-Change-Id: I4ab52b0884a909a4faeb6692f32d45878ea2838f
Gerrit-Change-Number: 8945
Gerrit-PatchSet: 4
Gerrit-Owner: Joe McDonnell <joemcdonnell@cloudera.com>
Gerrit-Reviewer: Impala Public Jenkins
Gerrit-Reviewer: Joe McDonnell <joemcdonnell@cloudera.com>
Gerrit-Reviewer: Mostafa Mokhtar <mmokhtar@cloudera.com>
Gerrit-Reviewer: Tim Armstrong <tarmstrong@cloudera.com>

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