[Impala-ASF-CR] IMPALA-2800: make memory maintenance less aggressive

["Tim Armstrong (Code Review)" <ge...@cloudera.org>]

Tim Armstrong has uploaded a new patch set (#2).

Change subject: IMPALA-2800: make memory maintenance less aggressive
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IMPALA-2800: make memory maintenance less aggressive

Memory maintenance isn't necessary for correctness - the MemTracker GC
functions are sufficient to free up memory before a mem limit would be
hit. So the main purpose of memory maintenance is to avoid holding onto
unneeded memory while the system is idle or under light load. It can
also help to redistribute memory between arenas in the buffer pool if
they have become imbalanced. Neither of these purposes require the
maintenance to be very aggressive aggressive.

* Simplify the heuristic for freeing and update the comments to reflect
  the current reality.
* Limit the rate at which TCMalloc releases memory to avoid it holding
  the global heap lock for a long time.
* Increase the memory maintenance interval - 1s is too aggressive and
  can free memory that will be imminently reused by a running query.

Change-Id: I0f822b294ab253d6f2828fc52f353aecaaf9b701
---
M be/src/common/init.cc
M be/src/util/memory-metrics.h
2 files changed, 26 insertions(+), 28 deletions(-)


  git pull ssh://gerrit.cloudera.org:29418/Impala-ASF refs/changes/26/6626/2
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Gerrit-MessageType: newpatchset
Gerrit-Change-Id: I0f822b294ab253d6f2828fc52f353aecaaf9b701
Gerrit-PatchSet: 2
Gerrit-Project: Impala-ASF
Gerrit-Branch: master
Gerrit-Owner: Tim Armstrong <ta...@cloudera.com>