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These settings are available in system.settings and are autogenerated from source.

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automatic_parallel_replicas_max_duplicated_read_ratio

How much of a query’s read volume may be read by every replica instead of being split between them, as a fraction of the whole, before automatic parallel replicas declines the query. Only the read parallel replicas coordinate is split; every other read of the same subtree runs on each replica in full. Those reads take the same wall-clock time either way, so the cost-model comparison is blind to them, but the cluster performs max_parallel_replicas times as much work for them. This setting is the limit on that waste: at the default 0.5 a query whose coordinated read is less than half of what it reads keeps running on one node, however the time comparison turns out. Set to 1 to accept any amount of duplicated reading, which restores the behaviour of only comparing times.

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automatic_parallel_replicas_min_bytes_per_replica

Threshold of bytes to read per replica to enable parallel replicas automatically (applies only when automatic_parallel_replicas_mode=1). 0 means no threshold. The total number of bytes to read is estimated based on the collected statistics.

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automatic_parallel_replicas_mode

Enable automatic switching to execution with parallel replicas based on collected statistics. Requires enable_parallel_replicas = 1, parallel_replicas_local_plan = 1 and providing cluster_for_parallel_replicas. With enable_parallel_replicas = 2 parallel replicas are forced and the automatic mode is not applied. 0 - disabled, 1 - enabled, 2 - only statistics collection is enabled (switching to execution with parallel replicas is disabled).

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automatic_parallel_replicas_remember_boundary

Lets automatic parallel replicas remember, per query plan, where the replicas’ share of the work ends, so that a repeated query whose statistics decline parallel replicas is decided without building the plan with parallel replicas. Disable it to make every query pay the full cost of the decision, e.g. when benchmarking that cost.