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Aurora (mysql): 63976 Internal write forwarding error

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Starting about three weeks ago, I'm getting the error "63976 Internal write forwarding error" roughly once a day, at unpredictable times and in random SQL write queries. The database setup and parameters have not changed in more than a year. The "ForwardingWriterOpenSessions" metric is low (no more than 5). The error appears once, not in (say) spurts that would indicate some kind of load problem.

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Aurora MySQL
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English

asked a year ago193 views

1 Answer
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The "63976 Internal write forwarding error" you're experiencing in Aurora MySQL with write forwarding enabled appears to be related to an internal issue in the write forwarding mechanism.

Based on similar issues reported with Aurora MySQL write forwarding, this could be due to several factors:

  1. Potential bug in the Aurora MySQL engine: There have been reports of assertion failures in the write forwarding mechanism, particularly with version 8.0.mysql_aurora.3.05.2. These failures can manifest as intermittent crashes or errors in the write forwarding process.

  2. Configuration issues: Even though your "ForwardingWriterOpenSessions" metric is low (no more than 5), there might be other configuration parameters affecting the write forwarding behavior.

Here are some steps you can take to address this issue:

  1. Check your Aurora MySQL version: If you're running version 8.0.mysql_aurora.3.05.2 or similar, consider upgrading to the latest minor version which may contain fixes for such issues.

  2. Review write forwarding parameters:

  • Ensure aurora_replica_read_consistency is properly set (typically to "SESSION")
  • Consider adjusting aurora_fwd_writer_idle_timeout to a higher value
  • Check aurora_fwd_writer_max_connections_pct is appropriate for your workload
  1. Monitor relevant metrics: Besides "ForwardingWriterOpenSessions", also monitor:
  • Aurora_fwd_replica_errors_session_limit
  • Aurora_fwd_replica_dml_stmt_count
  • Aurora_fwd_replica_dml_stmt_duration

  1. Check temporary table settings: If your workload involves complex queries that use temporary tables, ensure parameters like temptable_max_ram and temptable_max_mmap are adequately sized.

  2. Consider temporarily disabling write forwarding: As a diagnostic step, you could temporarily disable write forwarding to confirm if this is indeed the source of the error.

If the issue persists after these steps, it would be advisable to open a support case with AWS, as this may be related to an internal bug in the Aurora MySQL engine's write forwarding implementation.
Sources
Aurora MySQL Writer Instance Crashes Intermittently After Write Forwarding Is Enabled | AWS re:Post
Aurora MySQL regional cluster: cannot enable LocalWriteForwardingStatus | AWS re:Post
Amazon CloudWatch metrics and Aurora MySQL status variables for write forwarding - Amazon Aurora
Performance issues with Aurora MySQL Version 8.0 | AWS re:Post

answered a year ago

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