Disable query consolidation by default for master tablet types #4058
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dweitzman
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Feb 26, 2020
This diff creates the possibility to start a tablet with "-enable-consolidator=false -enable-consolidator-replicas" so that query consolidation is enabled only for non-master instance types. This allows using the consolidator while keeping the agreement that OLTP reads from master have read-committed consistency while replicas have inconsistent reads. See vitessio#4058 Signed-off-by: David Weitzman <dweitzman@pinterest.com>
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The documented consistency model is that master reads outside transactions have read-committed behavior (https://vitess.io/user-guide/scalability-philosophy/#consistency-model). This is not true in practice: query consolidation on master means that non-transactional master reads are not consistent
I think it makes more sense to default to the safe, intuitive behavior and let people opt-in to the riskier, higher throughput behavior if they feel it will provide value for their specific use cases.
Regardless of whether the default changes, having a flag to disable query consolidation only on master tablets seems valuable.
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