> On March 19, 2015, 9:40 a.m., Timothy Chen wrote:
> > src/slave/containerizer/fetcher.cpp, line 379
> > <https://reviews.apache.org/r/30774/diff/38/?file=899705#file899705line379>
> >
> >     benh, what do you think of Bernd's contentionBarrier injection? 
> > commonly we always just mock the callback (_fetch in this case) in tests to 
> > block, but Bernd wanted to introduce a specific empty method for tests. I 
> > told him this is not a pattern we use in Mesos, but like to see what you 
> > think.
> Bernd Mathiske wrote:
>     Of course I will stick to the prevalent patterns unless you start liking 
> this one :-)
> Bernd Mathiske wrote:
>     Turns out there is no method that offers itself opportunistically for the 
> prevalent pattern. The next call up is AFTER waiting for the futures that the 
> barrier needs to be BEFORE. Suggestions?
>     Alternatives (without judging them):
>     - Factor out the loop that gathers the futures and make it a method that 
> gets called once. Then mock this method and have it dual-purposed as 
> contention barrier. 
>     - Make the futures globally visible, await them in the test, too.
>     - Use an explicit lock instead of mocking.

Another option has been implemented in the latest patch: cut off the lower half 
of fetch() and call it _fetch(), then mock the latter. This variant ressembles 
existing other code the most.

- Bernd

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On April 30, 2015, 7:40 p.m., Bernd Mathiske wrote:
> -----------------------------------------------------------
> This is an automatically generated e-mail. To reply, visit:
> https://reviews.apache.org/r/30774/
> -----------------------------------------------------------
> (Updated April 30, 2015, 7:40 p.m.)
> Review request for mesos, Adam B, Benjamin Hindman, Till Toenshoff, and 
> Timothy Chen.
> Bugs: MESOS-2057, MESOS-2069, MESOS-2070, MESOS-2072, MESOS-2073, and 
> MESOS-2074
>     https://issues.apache.org/jira/browse/MESOS-2057
>     https://issues.apache.org/jira/browse/MESOS-2069
>     https://issues.apache.org/jira/browse/MESOS-2070
>     https://issues.apache.org/jira/browse/MESOS-2072
>     https://issues.apache.org/jira/browse/MESOS-2073
>     https://issues.apache.org/jira/browse/MESOS-2074
> Repository: mesos
> Description
> -------
> 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
> -----
>   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/containerizer/mesos/containerizer.hpp 
> 5e5f13ed8a71ff9510b40b6032d00fd16d312622 
>   src/slave/containerizer/mesos/containerizer.cpp 
> f2587280dc0e1d566d2b856a80358c7b3896c603 
>   src/slave/flags.hpp d3b1ce117fbb4e0b97852ef150b63f35cc991032 
>   src/slave/flags.cpp d0932b04e3825abb6173efe0d1aee199aa356932 
>   src/slave/slave.cpp c78ee3c9e7fc38ad364e83f4abe267e86bfbbc13 
>   src/tests/docker_containerizer_tests.cpp 
> c9d66b3fbc7d081f36c26781573dca50de823c44 
>   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/
> Testing
> -------
> 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.
> Thanks,
> Bernd Mathiske

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