Write-ahead log

    This module provides functionality for administering the write-ahead logs.Most of these functions only return sensible values when invoked with the MMFiles engine being active.

    retrieves the configuration of the write-ahead log

    Retrieves the configuration of the write-ahead log. The result is a JSONarray with the following attributes:

    • allowOversizeEntries: whether or not operations that are bigger than asingle logfile can be executed and stored
    • logfileSize: the size of each write-ahead logfile
    • historicLogfiles: the maximum number of historic logfiles to keep
    • reserveLogfiles: the maximum number of reserve logfiles that ArangoDBallocates in the background
    • throttleWait: the maximum wait time that operations will wait beforethey get aborted if case of write-throttling (in milliseconds)
    • throttleWhenPending: the number of unprocessed garbage-collectionoperations that, when reached, will activate write-throttling. A value of0 means that write-throttling will not be triggered.Examples

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    Configures the behavior of the write-ahead log. properties must be a JSONJSON object with the following attributes:

    • allowOversizeEntries: whether or not operations that are bigger than asingle logfile can be executed and stored
    • logfileSize: the size of each write-ahead logfile
    • reserveLogfiles: the maximum number of reserve logfiles that ArangoDBallocates in the background
    • throttleWait: the maximum wait time that operations will wait beforethey get aborted if case of write-throttling (in milliseconds)
    • throttleWhenPending: the number of unprocessed garbage-collectionoperations that, when reached, will activate write-throttling. A value of0 means that write-throttling will not be triggered.Specifying any of the above attributes is optional. Not specified attributeswill be ignored and the configuration for them will not be modified.

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    Flushing

    flushes the currently open WAL logfile

    The waitForSync option determines whether or not the operation shouldblock until the not-yet synchronized data in the write-ahead log wassynchronized to disk.

    The waitForCollector operation can be used to specify that the operationshould block until the data in the flushed log has been collected by thewrite-ahead log garbage collector. Note that setting this option to _true_might block for a long time if there are long-running transactions andthe write-ahead log garbage collector cannot finish garbage collection.

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