protoype for forceOneShardAttributeValue #14707
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* Lower priority of AQL lanes * Added CHANGELOG entry * Improved comments Co-authored-by: Vadim <vadim@arangodb.com>
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mchacki
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Sep 7, 2021
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I think the Part that is supposed for this forceOneShard is good. (Would approve)
However this PR seems to contain unrelated parts (especially request lanes in AQL)
I just want to avoid merging issues for the other PR, or having something included unter the radar). So maybe we need to make sure to merge in correct order.
If this comment is sorted out count this as approved!
tests/js/client/server_parameters/test-statistics-enabled-false.js
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…arangodb/arangodb into feature-3.8/forceOneShardAttributeValue
jsteemann
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Sep 7, 2021
mchacki
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Sep 7, 2021
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Scope & Purpose
Backport of #14701
Enterprise companion PR: https://github.com/arangodb/enterprise/pull/745
(Enterprise Edition only): added query option
forceOneShardAttributeValueto explicitly set a shard key value that will be used during query snippet distribution to limit the query to a specific server in the cluster.This query option can be used in complex queries in case the query optimizer cannot automatically detect that the query can be limited to only a single server (e.g. in a disjoint smart graph case).
When the option is set to the correct shard key value, the query will be limited to the target server determined by the shard key value. It thus requires that all collections in the query use the same distribution (i.e.
distributeShardsLikeattribute via disjoint SmartGraphs).Limiting the query to a single DB server is a performance optimization and may make complex queries run a lot faster because of the reduced setup and teardown costs and the reduced cluster-internal traffic during query execution.
If the option is set incorrectly, i.e. to a wrong shard key value, then the query may be shipped to a wrong DB server and may not return results (i.e. empty result set). It is thus the caller's responsibility to set the
forceOneShardAttributeValuecorrectly or not use it.The
forceOneShardAttributeValueoption will only honor string values. All other values as well as the empty string will be ignored and treated as if the option is not set.If the option is set and the query satisfies the requirements for using the option, the query's execution plan will contain the "cluster-one-shard" optimizer rule.
Backports:
Related Information
Testing & Verification