Common Configurations

Apache Flink provides several standard configuration settings that work across all file system implementations.

Default File System

A default scheme (and authority) is used if paths to files do not explicitly specify a file system scheme (and authority).

fs.default-scheme: <default-fs>

For example, if the default file system configured as fs.default-scheme: hdfs://localhost:9000/, then a file path of /user/hugo/in.txt is interpreted as hdfs://localhost:9000/user/hugo/in.txt.

Connection limiting

You can limit the total number of connections that a file system can concurrently open which is useful when the file system cannot handle a large number of concurrent reads/writes or open connections at the same time.

For example, small HDFS clusters with few RPC handlers can sometimes be overwhelmed by a large Flink job trying to build up many connections during a checkpoint.

To limit a specific file system’s connections, add the following entries to the Flink configuration. The file system to be limited is identified by its scheme.

fs.<scheme>.limit.total: (number, 0/-1 mean no limit)
fs.<scheme>.limit.input: (number, 0/-1 mean no limit)
fs.<scheme>.limit.output: (number, 0/-1 mean no limit)
fs.<scheme>.limit.timeout: (milliseconds, 0 means infinite)
fs.<scheme>.limit.stream-timeout: (milliseconds, 0 means infinite)

You can limit the number of input/output connections (streams) separately (fs.<scheme>.limit.input and fs.<scheme>.limit.output), as well as impose a limit on the total number of concurrent streams (fs.<scheme>.limit.total). If the file system tries to open more streams, the operation blocks until some streams close. If the opening of the stream takes longer than fs.<scheme>.limit.timeout, the stream opening fails.

To prevent inactive streams from taking up the full pool (preventing new connections to be opened), you can add an inactivity timeout which forcibly closes them if they do not read/write any bytes for at least that amount of time: fs.<scheme>.limit.stream-timeout.

Limit enforcment on a per TaskManager/file system basis. Because file systems creation occurs per scheme and authority, different authorities have independent connection pools. For example hdfs://myhdfs:50010/ and hdfs://anotherhdfs:4399/ will have separate pools.

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