> On April 12, 2015, 11:11 p.m., Timothy Chen wrote:
> > src/tests/fetcher_cache_tests.cpp, line 308
> > <https://reviews.apache.org/r/30774/diff/42/?file=922829#file922829line308>
> >
> >     Not sure why you picked an arbitrary number 5 here, why not let it be 
> > passed in?

OK, I will add an explanation in a comment. Two requirements need to be met by 
this constant.
- It needs to be larger than the expected number of status updates. We might 
choose something much larger than 5, but all tests run just fine with 5.
- It needs to be finite. Otherwise we will keep waiting for updates when none 
arrive due to a bug.

However, if we passed this constant in, then we would need to explain it at all 
the call sites, i.e. multiple times instead of only once. But the situation is 
exactly the same every time. So I will refrain from that.


- Bernd


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On April 10, 2015, 4:33 a.m., Bernd Mathiske wrote:
> 
> -----------------------------------------------------------
> This is an automatically generated e-mail. To reply, visit:
> https://reviews.apache.org/r/30774/
> -----------------------------------------------------------
> 
> (Updated April 10, 2015, 4:33 a.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 3a8e8bf303e0576c212951f6028af77e54d93537 
>   include/mesos/type_utils.hpp cdf5864389a72002b538c263d70bcade2bdffa45 
>   src/Makefile.am fa609da08e23d6595a3f6d2efddd3e333b6c78f1 
>   src/hdfs/hdfs.hpp 968545d9af896f3e72e156484cc58135405cef6b 
>   src/launcher/fetcher.cpp 796526f59c25898ef6db2b828b0e2bb7b172ba25 
>   src/slave/constants.hpp fd1c1aba0aa62372ab399bee5709ce81b8e92cec 
>   src/slave/containerizer/docker.hpp 6893684e6d199a5d69fc8bba8e60c4acaae9c3c9 
>   src/slave/containerizer/docker.cpp f9fb07806e3b7d7d2afc1be3b8756eac23b32dcd 
>   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 
> e4136095fca55637864f495098189ab3ad8d8fe7 
>   src/slave/flags.hpp d3b1ce117fbb4e0b97852ef150b63f35cc991032 
>   src/slave/flags.cpp 35f56252cfda5011d21aa188f33cc3e68a694968 
>   src/slave/slave.cpp 9fec023b643d410f4d511fa6f80e9835bab95b7e 
>   src/tests/docker_containerizer_tests.cpp 
> c772d4c836de18b0e87636cb42200356d24ec73d 
>   src/tests/fetcher_cache_tests.cpp PRE-CREATION 
>   src/tests/fetcher_tests.cpp 4549e6a631e2c17cec3766efaa556593eeac9a1e 
>   src/tests/mesos.hpp 0e98572a62ae05437bd2bc800c370ad1a0c43751 
>   src/tests/mesos.cpp 02cbb4b8cf1206d0f32d160addc91d7e0f1ab28b 
> 
> 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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