Errors are handled at two levels.
A @apidoc[HandlerRecoveryStrategy] can be defined for the Projection to specify what to do when processing of an envelope fails. The alternatives are:
fail - If the first attempt to invoke the handler fails it will immediately give up and the projection will be @ref:restarted.skip - If the first attempt to invoke the handler fails it will immediately give up, discard the element and continue with next.retryAndFail(retries, delay) - If the first attempt to invoke the handler fails it will retry invoking the handler with the same envelope a number of retries with the delay between each attempt. It will give up and @ref:restart the projection if all attempts fail.retryAndSkip(retries, delay) - If the first attempt to invoke the handler fails it will retry invoking the handler with the same envelope a number of retries with the delay between each attempt. It will give up, discard the element and continue with next if all attempts fail.The following example is using the CassandraProjection but the same can be used with any other @ref:Projection type.
The HandlerRecoveryStrategy can be defined withRecoveryStrategy:
Scala : @@snip CassandraProjectionDocExample.scala { #withRecoveryStrategy }
Java : @@snip CassandraProjectionDocExample.java { #withRecoveryStrategy }
If the recovery strategy is not defined on the Projection the default is fail, and that can be defined in configuration:
@@snip reference.conf { #recovery-strategy }
The Projection will be restarted if it fails, for example if the offset can't be saved or processing of an envelope fails after applying the @ref:Handler recovery. Restart means that the projection is restarted from latest saved offset. Projections are restarted in case of failures by default, but it can be customized.
The following example is using the CassandraProjection but the same can be used with any other @ref:Projection type.
The restart can be defined with exponential backoff settings:
Scala : @@snip CassandraProjectionDocExample.scala { #withRestartBackoff }
Java : @@snip CassandraProjectionDocExample.java { #withRestartBackoff }
If the recovery strategy is not defined on the Projection the default is defined in configuration:
@@snip reference.conf { #restart-backoff }