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# File Logger

## Overview

The FileLogger writes samples to a file stored on a persistent storage device, such as the flash file system.

Warning

The ConnectPort products on which Dia is written to run have limitations on the number of files which may be held open simultaneously. Multiple files also impede performance. It is recommended that a single logger be used. If necessary, the file can be post-processed and filtered to extract information. The resulting log files are platform independent and may be copied to a host PC for analysis. If this is not possible, keep the overall file count low.

## Configuration

A typical FileLogger configuration block looks like this:

    - name: file_logger
      driver: channels.logging.file_logger.file_logger:FileLogger
      settings:
          filename: WEB/python/dia.log
          event_volume_size_k: 512
          include_channel_prefixes:
           - template
           - sensor0
          exclude_channel_prefixes:
           - sensor0.temperature
           - noisy_device.channel
          sample_index_frequency: 128

### Settings

#### Log Creation

filename (required)
  Absolute path to the file that will be created and/or read.
event_volume_size_k (required)
  Size in kilobytes of the event portion of the log. The resulting file will be larger than the size specified in order to store additional information about the system.

#### Operating Parameters

sample_index_frequency (optional)
  The log will store an index of the total state of the system after the configured number of events. Lower numbers will speed up random access to events in the log at the cost of decreasing the number of events that the log can store.
include_channel_prefixes (optional)
  If specified, this parameter will determine the list of prefixes to channels that will be stored in this log.
exclude_channel_prefixes (optional)
  If specified, this parameter will determine the list of prefixes to channels that willnot be stored in this log. If both `include_channel_prefixes``and ``exclude_channel_prefixes` are specified, the include list is calculated first, and then prefixes from the exclude list are removed from the result.

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