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From "Bernd Mathiske" <>
Subject Re: Review Request 30774: Fetcher Cache
Date Sun, 01 Mar 2015 10:35:30 GMT

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(Updated March 1, 2015, 2:35 a.m.)

Review request for mesos, Adam B, Benjamin Hindman, Till Toenshoff, and Timothy Chen.


Improved fetcher cache tests, introduced two cache eviction tests. One tests whether eviction
succeeds, the other also tests what happens if it fails.

Bugs: MESOS-2057, MESOS-2069, MESOS-2070, MESOS-2072, MESOS-2073, and MESOS-2074

Repository: mesos


Almost all of the functionality in epic MESOS-336. Downloaded files from CommandInfo::URIs
can now be cached in a cache directory designated by a slave flag. This only happens when
asked for by an extra flag in the URI and is thus backwards-compatible. The cache has a size
limit also given by a new slave flag. Cache-resident files are evicted as necessary to make
space for newly fetched ones. Concurrent attempts to cache the same URI leads to only one
download. The fetcher program remains external for safety reasons, but is now augmented with
more elaborate parameters packed into a JSON object to implement specific fetch actions for
all of the above. Additional testing includes fetching from (mock) HDFS and coverage of the
new features.

Diffs (updated)

  include/mesos/fetcher/fetcher.proto 311af9aebc6a85dadba9dbeffcf7036b70896bcc 
  include/mesos/mesos.proto 9df972d750ce1e4a81d2e96cc508d6f83cad2fc8 
  src/ 17d0d7aa7361c3a373f6863d36b0a4767f5c05c4 
  src/hdfs/hdfs.hpp 968545d9af896f3e72e156484cc58135405cef6b 
  src/launcher/fetcher.cpp 796526f59c25898ef6db2b828b0e2bb7b172ba25 
  src/slave/constants.hpp fd1c1aba0aa62372ab399bee5709ce81b8e92cec 
  src/slave/containerizer/docker.hpp b7bf54ac65d6c61622e485ac253513eaac2e4f88 
  src/slave/containerizer/docker.cpp 5f4b4ce49a9523e4743e5c79da4050e6f9e29ed7 
  src/slave/containerizer/fetcher.hpp 1db0eaf002c8d0eaf4e0391858e61e0912b35829 
  src/slave/containerizer/fetcher.cpp 9e9e9d0eb6b0801d53dec3baea32a4cd4acdd5e2 
  src/slave/containerizer/mesos/containerizer.hpp ae61a0fcd19f2ba808624312401f020121baf5d4

  src/slave/containerizer/mesos/containerizer.cpp ec4626f903d44c0911093ff763ef16ad27c418a9

  src/slave/flags.hpp 56b25caf3901b38bdecb50310e8bcae0b114efa8 
  src/slave/slave.cpp 9f31fa46304398e8f87b41b55d8f4cfd4aba10b9 
  src/tests/docker_containerizer_tests.cpp 06cd3d89ecbaaac17ae6970604b21fbe29f6e887 
  src/tests/fetcher_cache_tests.cpp PRE-CREATION 
  src/tests/fetcher_tests.cpp 0ae0a10b41a2c0f7459c771b31c76bbc0c02df4f 
  src/tests/mesos.hpp f7a0d057edea1a7ec7ae3bb9bc729230bf7dd46d 
  src/tests/mesos.cpp 23f790cbb289f6483dcdfa6ecccd462360ce02f1 



make check

--- longer Description: ---

-Replaces all other reviews for the fetcher cache except those related to stout: 30006, 30033,
30034, 30036, 30037, 30039, 30124, 30173, 30614, 30616, 30618, 30621, 30626. See descriptions
of those. In dependency order:

30033: Removes the fetcher env tests since these won't be needed any more when the fetcher
uses JSON in a single env var as a parameter. They never tested anything that won't be covered
by other tests anyway.

30034: Makes the code structure of all fetcher tests the same. Instead of calling the run
method of the fetcher directly, calling through fetch(). Also removes all uses of I/O redirection,
which is not really needed for debugging, and thus the next patch can refactor fetch() and
run(). (The latter comes in two varieties, which complicates matters without much benefit.)

30036: Extends the CommandInfo::URI protobuf with a boolean "caching" field that will later
cause fetcher cache actions. Also introduces the notion of a cache directory to the fetcher
info protobuf. And then propagates these additions throughout the rest of the code base where
applicable. This includes passing the slave ID all the way down to the place where the cache
dir name is constructed.

30037: Extends the fetcher info protobuf with "actions" (fetch directly bypassing the cache,
fetch through the cache, retrieve from the cache). Switches the basis for dealing with uris
to "items", which contain the uri, the action, and potentially a cache file name. Refactors
fetch() and run(), so there is only one of each. Introduces about half of the actual cache
logic, including a hashmap of cache file objects for bookkeeping and basic operations on it.

30039: Enables fetcher cache actions in the mesos fetcher program.

30006: Enables concurrent downloading into the fetcher cache. Reuse of download results in
the cache when multiple fetcher runs occur concurrently. 

30614: This is to ensure that all this refactoring of fetcher code has not broken HDFS fetching.
Adds a test that exercises the C++ code paths in Mesos and mesos-fetcher related to fetching
from HDFS. Uses a mock HDFS client written in bash that acts just like a real "hadoop" command
if used in the right limited way.

30124: Inserted fetcher cache zap upon slave startup, recovery and shutdown. This implements
recovery in an acceptable, yet most simple way.

30173: Created fetcher cache tests. Adds a new test source file containing a test fixture
and tests to find out if the fetcher cache works with a variety of settings.

30616: Adds hdfs::du() which calls "hadoop fs -du -h" and returns a string that contains the
file size for the URI passed as argument. This is needed to determine the size of a file on
HDFS before downloading it to the fetcher cache (to ensure there is enough space).

30621: Refactored URI type separation in mesos-fetcher. Moved the URI type separation code
(distinguishes http, hdfs, local copying, etc.) from mesos-fetcher to the fetcher process/actor,
since it is going to be reused by download size queries when we introduce fetcher cache management.
Also factored out URI validation, which will be used the same way by mesos-fetcher and the
fetcher process/actor.

30626: Fetcher cache eviction. This happens when the cache does not have enough space to accomodate
upcoming downloads to the cache. Necessary provisions included here:
- mesos-fetcher does not run until evictions have been successful
- Cache space is reserved while (async) waiting for eviction to succeed. If it fails, the
reservation gets undone.
- Reservations can be partly from available space, partly from evictions. All math included
- To find out how much space is needed, downloading has a prelude in which we query the download
size from the URI. This works for all URI types that mesos-fetcher currently supports, including
http and hdfs.
- Size-determination requests are now synchronized, too. Only one per URI in play happens.
- There is cleanup code for all kinds of error situations. At the very end of the fetch attempt,
each list is processed for undoing things like space reservations and eviction disabling.
- Eviction gets disabled for URIs that are currently in use, i.e. the related cache files
are. We use reference counting for this, since there may be concurrent fetch attempts using
the same cache files.


Bernd Mathiske

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