[OAK-2106] Optimize reads from secondaries

• Type: Improvement
• Status: Resolved
• Priority: Major
• Resolution: Duplicate
• Component/s: core, mongomk
• Labels: performance scalability
• Epic Link: DocumentMK scalability improvements
• Assignee: Tomek Rękawek
• Reporter: Marcel Reutegger
• Created: 18/Sep/14 07:17
• Updated: 22/Mar/16 09:23
• Resolved: 22/Mar/16 09:23

Description

OAK-1645 introduced support for reads from secondaries under certain
conditions. The current implementation checks the _lastRev on a potentially
cached parent document and reads from a secondary if it has not been
modified in the last 6 hours. This timespan is somewhat arbitrary but
reflects the assumption that the replication lag of a secondary shouldn't
be more than 6 hours.

This logic should be optimized to take the actual replication lag into
account. MongoDB provides information about the replication lag with
the command rs.status().

Issue Links

• is superceded by: OAK-3865 New strategy to optimize secondary reads
• relates to: OAK-1750 Adapt write concern dynamically to manage replication lag