improve query plan serialization time #17897
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* Added new stage "instantiating executors" to the query profiling output. The time spent in "instantiating executors" is the time needed to create the query executors from the final query execution time. In cluster mode, this stage also includes the time needed for physically distributing the query snippets to the participating database servers. Previously, the time spent for instantiating executors and the physical distribution was contained in the "optimizing plan" stage, which was misleading. * Remove constant values for query variables from query plan serialization in cases they were not needed. Previously, constant values of query variables were always serialized for all occurrences of a variable in a query plan. If the constant values were large, this contributed to higher serialization and thus query setup times. Now the constant values are only serialized for relevant parts of query execution plans.
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Scope & Purpose
Improve query plan serialization time
Added new stage "instantiating executors" to the query profiling output. The time spent in "instantiating executors" is the time needed to create the query executors from the final query execution time. In cluster mode, this stage also includes the time needed for physically distributing the query snippets to the participating database servers. Previously, the time spent for instantiating executors and the physical distribution was contained in the "optimizing plan" stage, which was misleading.
Remove constant values for query variables from query plan serialization in cases they were not needed. Previously, constant values of query variables were always serialized for all occurrences of a variable in a query plan. If the constant values were large, this contributed to higher serialization and thus query setup times. Now the constant values are only serialized for relevant parts of query execution plans.
The relevant change in this PR that has the largest effect on performance is that the
toVelocyPack(...)method ofaql::Variablenow doesn't include constant values anymore. There is new overload of that method that will also include constant values, but it has to be called explicitly. This is now done only in a few dedicated places. All other places that calltoVelocyPack(...)will call the method that doesn't serialize the constant values.The rest of this PR contains a bit of cleanup, which is not relevant for the performance improvement.
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