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Chandni Singh commented on APEXMALHAR-2063: ------------------------------------------- Yes. Managed State flushes data only at checkpoints. > Integrate WAL to FS WindowDataManager > ------------------------------------- > > Key: APEXMALHAR-2063 > URL: https://issues.apache.org/jira/browse/APEXMALHAR-2063 > Project: Apache Apex Malhar > Issue Type: Improvement > Reporter: Chandni Singh > Assignee: Chandni Singh > > FS Window Data Manager is used to save meta-data that helps in replaying > tuples every completed application window after failure. For this it saves > meta-data in a file per window. Having multiple small size files on hdfs > cause issues as highlighted here: > http://blog.cloudera.com/blog/2009/02/the-small-files-problem/ > Instead FS Window Data Manager can utilize the WAL to write data and maintain > a mapping of how much data was flushed to WAL each window. > In order to use FileSystemWAL for replaying data of a finished window, there > are few changes made to FileSystemWAL this is because of following: > 1. WindowDataManager needs to reply data of every finished window. This > window may not be checkpointed. > FileSystemWAL truncates the WAL file to the checkpointed point after recovery > so this poses a problem. > WindowDataManager should be able to control recovery of FileSystemWAL. > 2. FileSystemWAL writes to temporary files. The mapping of temp files to > actual file is part of its state which is checkpointed. Since > WindowDataManager replays data of a window not yet checkpointed, it needs to > know the actual temporary file the data is being persisted to. > At a high level, WindowDataManager will persist meta information on file > system which includes following details for every window > - start wal pointer > - end was pointer > - wal file path > This is a single file which is updated every end-window along with the actual > data in WAL file. -- This message was sent by Atlassian JIRA (v6.3.4#6332)