Hello Thomas Marshall, Lars Volker, David Rorke, Sahil Takiar, Todd Lipcon, Tim
Armstrong, Joe McDonnell, Impala Public Jenkins,
I'd like you to reexamine a change. Please visit
http://gerrit.cloudera.org:8080/12987
to look at the new patch set (#2).
Change subject: IMPALA-8341: Data cache for remote reads
......................................................................
IMPALA-8341: Data cache for remote reads
This is a patch based on PhilZ's prototype:
https://gerrit.cloudera.org/#/c/12683/
This change implements an IO data cache which is backed by
local storage. It implicitly relies on the OS page cache
management to shuffle data between memory and the storage
device. This is useful for caching data read from remote
filesystems (e.g. remote HDFS data node, S3, ABFS, ADLS).
A data cache is divided into one or more partitions based on
the configuration string which is a list of directories, separated
by comma, followed by the storage capacity per directory.
An example configuration string is like the following:
--data_cache_config=/data/0,/data/1:150GB
In the configuration above, the cache may use up to 300GB of
storage space, with 150GB max for /data/0 and /data/1 respectively.
Each partition has a meta-data cache which tracks the mappings
of cache keys to the locations of the cached data. A cache key
is a tuple of (file's name, file's modification time, file offset)
and a cache entry is a tuple of (backing file, offset in the backing
file, length of the cached data, optional checksum). Note that the
cache currently doesn't support overlapping ranges. In other words,
if the cache contains an entry of a file for range [m, m+4MB), a lookup
for [m+4K, m+8K) will miss in the cache. In practice, we haven't seen
this as a problem but this may require further evaluation in the future.
Each partition stores its set of cached data in backing files created
on local storage. When inserting new data into the cache, the data is
appended to the current backing file in use. The storage consumption
of each cache entry counts towards the quota of that partition. When a
partition reaches its capacity, the least recently used (LRU) data in
that partition is evicted. Evicted data is removed from the underlying
storage by punching holes in the backing file it's stored in. As a
backing file reaches a certain size (by default 4TB), new data will
stop being appended to it and a new file will be created instead. Note
that due to hole punching, the backing file is actually sparse.
Optionally, checksumming can be enabled to verify read from the cache
is consistent with what was inserted and to verify that multiple attempted
insertions with the same cache key have the same cache content.
Checksumming is enabled by default for debug builds.
To probe for cached data in the cache, the interface Lookup() is used;
To insert data into the cache, the interface Store() is used. Please note
that eviction happens inline currently during Store().
This patch also added two startup flags for start-impala-cluster.py:
'--data_cache_dir' specifies the base directory in which each Impalad
creates the caching directory
'--data_cache_size' specifies the capacity string for each cache directory.
Testing done: a new BE test was added; core test with cache enabled.
Perf:
- 16-streams TPCDS at 3TB in a 20 node S3 cluster shows about 30% improvement
over runs without the cache. Each node has a cache size of 150GB per node.
The performance is at parity with a configuration of a HDFS cluster using
EBS as the storage.
Change-Id: I734803c1c1787c858dc3ffa0a2c0e33e77b12edc
---
M be/src/exec/hdfs-scan-node-base.cc
M be/src/exec/hdfs-scan-node-base.h
M be/src/runtime/io/CMakeLists.txt
A be/src/runtime/io/data-cache-test.cc
A be/src/runtime/io/data-cache.cc
A be/src/runtime/io/data-cache.h
M be/src/runtime/io/disk-io-mgr.cc
M be/src/runtime/io/disk-io-mgr.h
M be/src/runtime/io/hdfs-file-reader.cc
M be/src/runtime/io/hdfs-file-reader.h
M be/src/runtime/io/request-context.h
M be/src/util/filesystem-util.cc
M be/src/util/filesystem-util.h
M be/src/util/impalad-metrics.cc
M be/src/util/impalad-metrics.h
M bin/start-impala-cluster.py
M common/thrift/metrics.json
17 files changed, 1,467 insertions(+), 29 deletions(-)
git pull ssh://gerrit.cloudera.org:29418/Impala-ASF refs/changes/87/12987/2
--
To view, visit http://gerrit.cloudera.org:8080/12987
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Gerrit-Project: Impala-ASF
Gerrit-Branch: master
Gerrit-MessageType: newpatchset
Gerrit-Change-Id: I734803c1c1787c858dc3ffa0a2c0e33e77b12edc
Gerrit-Change-Number: 12987
Gerrit-PatchSet: 2
Gerrit-Owner: Michael Ho <k...@cloudera.com>
Gerrit-Reviewer: David Rorke <dro...@cloudera.com>
Gerrit-Reviewer: Impala Public Jenkins <impala-public-jenk...@cloudera.com>
Gerrit-Reviewer: Joe McDonnell <joemcdonn...@cloudera.com>
Gerrit-Reviewer: Lars Volker <l...@cloudera.com>
Gerrit-Reviewer: Michael Ho <k...@cloudera.com>
Gerrit-Reviewer: Sahil Takiar <stak...@cloudera.com>
Gerrit-Reviewer: Thomas Marshall <tmarsh...@cloudera.com>
Gerrit-Reviewer: Tim Armstrong <tarmstr...@cloudera.com>
Gerrit-Reviewer: Todd Lipcon <t...@apache.org>
