Archivematica 1.8 is our latest release.

Task output capturing configuration

Archivematica allows users to configure their MCP client(s) in order to control whether or not output streams (stdout and stderr) from the client scripts are captured and then passed from the task workers to the task manager (the MCP server).

In the default configuration, these output streams are captured. In this state, when a user clicks on the gear icon of a microservice in order to view the tasks that have run, each task representation will contain a section entitled Standard streams which will contain a sub-section entitled Standard output (stdout) containing the stdout from the client script and another entitled Standard error (stderr) containing the stderr.

However, in some cases, serializing these output streams and moving them around (capturing them) can have a non-trivial performance cost. (We have measured a 6% reduction in processing time for some transfers when output capturing is disabled.) Archivematica can be configured to avoid paying this cost by disabling the capturing of these output streams. The trade-off for doing this is that the stdout and stderr that documents the running of a preservation task will no longer be stored in the database and it will no longer be displayed in the tasks interface.

In order to configure Archivematica to stop capturing output streams, one must set the ARCHIVEMATICA_MCPCLIENT_MCPCLIENT_CAPTURE_CLIENT_SCRIPT_OUTPUT environment variable to false before starting (or re-starting) the MCP client process. The way that Archivematica environment variables are set depends on the deployment method used. Please consult the relevant documentation for your deployment method if you are interested in disabling output capturing.

Note that when output capturing is disabled the stdout will never be captured while the stderr will only be captured when the preservation task returns a non-zero exit code (i.e., when it fails). This allows the user to get the performance benefits while still having useful debugging information in the case where a task fails.

Tip

It is also possible to tweak the configuration of your database server in order to push the existing limits further. This can be a good solution for users familiar with the MySQL storage engine. In particular we have had some success increasing the InnoDB log file size (innodb_log_file_size). See Should MySQL update the default innodb_log_file_size? for more. In the long term, we expect to find better ways to store task results - if you are interested, please see issue #314.

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