[jira] [Closed] (FLINK-5763) Make savepoints self-contained and relocatable

["Stephan Ewen (JIRA)" <ji...@apache.org>]

     [ https://issues.apache.org/jira/browse/FLINK-5763?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

Stephan Ewen closed FLINK-5763.
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> Make savepoints self-contained and relocatable
> ----------------------------------------------
>
>                 Key: FLINK-5763
>                 URL: https://issues.apache.org/jira/browse/FLINK-5763
>             Project: Flink
>          Issue Type: Improvement
>          Components: State Backends, Checkpointing
>            Reporter: Ufuk Celebi
>            Assignee: Ufuk Celebi
>             Fix For: 1.3.0
>
>
> After a user has triggered a savepoint, a single savepoint file will be returned as a handle to the savepoint. A savepoint to {{<target>}} creates a savepoint file like {{<target>/savepoint-<randomSuffix>}}.
> This file contains the metadata of the corresponding checkpoint, but not the actual program state. While this works well for short term management (pause-and-resume a job), it makes it hard to manage savepoints over longer periods of time.
> h4. Problems
> h5. Scattered Checkpoint Files
> For file system based checkpoints (FsStateBackend, RocksDBStateBackend) this results in the savepoint referencing files from the checkpoint directory (usually different than <target>). For users, it is virtually impossible to tell which checkpoint files belong to a savepoint and which are lingering around. This can easily lead to accidentally invalidating a savepoint by deleting checkpoint files.
> h5. Savepoints Not Relocatable
> Even if a user is able to figure out which checkpoint files belong to a savepoint, moving these files will invalidate the savepoint as well, because the metadata file references absolute file paths.
> h5. Forced to Use CLI for Disposal
> Because of the scattered files, the user is in practice forced to use Flink’s CLI to dispose a savepoint. This should be possible to handle in the scope of the user’s environment via a file system delete operation.
> h4. Proposal
> In order to solve the described problems, savepoints should contain all their state, both metadata and program state, inside a single directory. Furthermore the metadata must only hold relative references to the checkpoint files. This makes it obvious which files make up the state of a savepoint and it is possible to move savepoints around by moving the savepoint directory.
> h5. Desired File Layout
> Triggering a savepoint to {{<target>}} creates a directory as follows:
> {code}
> <target>/savepoint-<jobId>-<randomSuffix>
>   +-- _metadata
>   +-- data-<randomSuffix> [1 or more]
> {code}
> We include the JobID in the savepoint directory name in order to give some hints about which job a savepoint belongs to.
> h5. CLI
> - Trigger: When triggering a savepoint to {{<target>}} the savepoint directory will be returned as the handle to the savepoint.
> - Restore: Users can restore by pointing to the directory or the _metadata file. The data files should be required to be in the same directory as the _metadata file.
> - Dispose: The disposal command should be deprecated and eventually removed. While deprecated, disposal can happen by specifying the directory or the _metadata file (same as restore).



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