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    Let's also 'hash_combine' the 'extract' and 'executable' information here 


    Great TODO, let's point the comments in slave.cpp to this TODO please!


    This function no longer exists!


    +4 please!


    Not used!


    Two spaces between top-level definitions please!


    Please comment/TODO why this is being used and that you plan to remove this 
once we have C++11 lambdas!


    How about still calling this s/reference/get/ and then checking the 
references? Also, we're deprecating and removing the return value of const &. 
    Option<shared_ptr<Cache::Entry>>& entry =
      cache.get(commandUser, uri.value());
    if (entry.isSome()) {
      CHECK(entry.get()->references() > 0);


    +2 not +4


    Let's get a CHECK here too:
    CHECK(newEntry->references() > 0);


    Let's move this comment to the top of this function so that readers of the 
code have a better idea of what we're trying to accomplish sooner!


    Let's add another comment to remind readers why if the entry's 'completion' 
is still pending this implies that we need to DOWNLOAD_AND_CACHE? For example:
    // Since the entry is not yet "complete", i.e., 'completion().isPending()', 
    // then it must be the case that we created the entry in
    // FetcherProcess::fetch otherwise the entry should have been
    // in the cache and we would have waited for the completion in
    // FetcherProcess::fetch.


    s/recoverCache/recover/ <-- Since in the future there might be other 
"recovery" things that need to get done that doesn't have anything to do with 
the cache.
    Also, let's please leave a comment here that explains why we're calling a 
static method rather than invoking a method on an instance of a 'Fetcher' 
directly. Our intuition is that this will likely have to change in the future.


    Comment here too, please, thanks!

- Benjamin Hindman

On April 29, 2015, 8:42 p.m., Bernd Mathiske wrote:
> -----------------------------------------------------------
> This is an automatically generated e-mail. To reply, visit:
> https://reviews.apache.org/r/30774/
> -----------------------------------------------------------
> (Updated April 29, 2015, 8:42 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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