Indexer Metrics

[neekolas]

• Gauge of current block being indexed
• Gauge of current block on chain
• Distance between current block and indexer progress (how far behind the head of the chain are we)
• Number of messages processed (per contract)
• Message validation and storage error/success rates
• Number of retryable errors reached in message storer

See more info in Milestone https://github.com/xmtp/xmtpd/milestone/9