Module limit_pushdown 

LimitPushdown pushes LIMIT down through ExecutionPlans to reduce data transfer as much as possible.

Structs

GlobalRequirements

This is a “data class” we use within the LimitPushdown rule to push down LimitExec in the plan. GlobalRequirements are hold as a rule-wide state and holds the fetch and skip information. The struct also has a field named satisfied which means if the “current” plan is valid in terms of limits or not.

LimitPushdown

This rule inspects ExecutionPlan’s and pushes down the fetch limit from the parent to the child if applicable.

Enums

LimitExec

This enumeration makes skip and fetch calculations easier by providing a single API for both local and global limit operators.

Functions

add_global_limit 🔒

Adds a global limit to the plan.

add_limit 🔒

Adds a limit to the plan, chooses between global and local limits based on skip value and the number of partitions.

combines_input_partitions 🔒

Checks if the given plan combines input partitions.

extract_limit 🔒

Transforms the ExecutionPlan into a LimitExec if it is a GlobalLimitExec or a LocalLimitExec.

pushdown_limit_helper

This function is the main helper function of the LimitPushDown rule. The helper takes an ExecutionPlan and a global (algorithm) state which is an instance of GlobalRequirements and modifies these parameters while checking if the limits can be pushed down or not.

pushdown_limits 🔒

Pushes down the limit through the plan.