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(Updated May 4, 2015, 4:29 p.m.)
Review request for mesos, Adam B, Benjamin Hindman, Till Toenshoff, and Timothy
Addressed most open issues. The rest will be dealt with soon.
Bugs: MESOS-2057, MESOS-2069, MESOS-2070, MESOS-2072, MESOS-2073, and MESOS-2074
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.
--- 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
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
30626: Fetcher cache eviction. This happens when the cache does not have enough
space to accomodate upcoming downloads to the cache. Necessary provisions
- 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
- 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.