Page History

...

• Define a target topic fetch RPC size:
  • Let metadataExpirySecs = metadata.expiry.ms / 1000
  • Set topicsPerSec = <number of cached topics> / metadataExpirySecs
  • Set targetMetadataFetchSize = Math.max(topicsPerSec / 10, 20)
    • Rationale: this sets the target size to be approximate a metadata refresh at least every 10 seconds, while also maintaining a reasonable batch size of '20' for setups with a lower number of topics. '20' has no significance other than it's a small-but-appropriate trade-off between RPC metadata response size and necessary RPC frequency.
• Maintain a collection T (urgent) of all topics
  • with no cached metadata and buffered producer request data
  • that were notified of a metadata change (e.g. NOT_LEADER_FOR_PARTITION encountered)
  • with metadata that hasn't been refreshed at least 'metadata.max.age.ms' ago
• Maintain a collection U (non-urgent) of all topics
  • not contained in T
  • with metadata that hasn't been refreshed for at least 'metadata.max.age.ms * 0.5' ago
    • Rationale: A multiplier of 0.5 is presumed to be a reasonable time at which refreshing the metadata could be beneficial, with enough duration to allow for slack between when the metadata update is necessary.
• If T is non-empty
  • fetch metadata for all topics in T
  • fetch metadata for a subset of topics in U, such that '|T + sub(U)| <= TARGET_METADATA_FETCH_SIZE'
• If '|U| >= TARGET_METADATA_FETCH_SIZE'
  • fetch metadata for TARGET_METADATA_FETCH_SIZE topics in U with the oldest last refresh times

...