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(Updated May 12, 2015, 3:43 p.m.)

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


Minor cleanups, mostly removing & from const assignments.

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)

  docs/configuration.md 54c4e31ed6dfed3c23d492c19a301ce119a0519b 
  docs/fetcher-cache-internals.md PRE-CREATION 
  docs/fetcher.md PRE-CREATION 
  include/mesos/fetcher/fetcher.proto 311af9aebc6a85dadba9dbeffcf7036b70896bcc 
  include/mesos/mesos.proto 967b1e3bbfb3f6b71d5a15d02cba7ed5ec21816f 
  include/mesos/type_utils.hpp 044637481e5405d4d6f61653a9f9386edd191deb 
  src/Makefile.am 93c7c8a807a33ab639be6289535bbd32022aa85b 
  src/hdfs/hdfs.hpp 968545d9af896f3e72e156484cc58135405cef6b 
  src/launcher/fetcher.cpp 796526f59c25898ef6db2b828b0e2bb7b172ba25 
  src/slave/constants.hpp fd1c1aba0aa62372ab399bee5709ce81b8e92cec 
  src/slave/containerizer/docker.hpp b25ec55bf3cd30d6e8a804d09d90c632a7d12e3f 
  src/slave/containerizer/docker.cpp f9fc89ad7e3c853c3f9f6dcf9aa68e54dc1888c6 
  src/slave/containerizer/fetcher.hpp 1db0eaf002c8d0eaf4e0391858e61e0912b35829 
  src/slave/containerizer/fetcher.cpp 9e9e9d0eb6b0801d53dec3baea32a4cd4acdd5e2 
  src/slave/flags.hpp d3b1ce117fbb4e0b97852ef150b63f35cc991032 
  src/slave/flags.cpp d0932b04e3825abb6173efe0d1aee199aa356932 
  src/slave/slave.cpp c78ee3c9e7fc38ad364e83f4abe267e86bfbbc13 
  src/tests/fetcher_cache_tests.cpp PRE-CREATION 
  src/tests/fetcher_tests.cpp 4549e6a631e2c17cec3766efaa556593eeac9a1e 
  src/tests/mesos.hpp 19db71217f0a3f1ab17a6fd4408f8251410d731d 
  src/tests/mesos.cpp bc082e8d91deb2c5dd64bbc3f0a8a50fa7d19264 

Diff: https://reviews.apache.org/r/30774/diff/


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 

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 

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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