Adding page for CBO

[premkumr]

@netlify /preview/architecture/query-layer/planner-optimizer
DOC-383

[netlify]

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[gauravk-in]

It generates various plans of execution and determines the optimal path by taking into consideration the costs associated various factors like index lookups, scans, CPU usage, network latency, and so on.

Is missing ... costs associated *with* various factors...

Could also be rephrased as,

It computes the cost of various execution plans by taking into consideration factors such as index lookup, CPU usage, network throughput, and so on and picks the plan with the cheapest cost.

[gauravk-in]

The primary component that calculates these values is the cost-based optimizer (CBO).

can be

The query planner, also known as CBO comprises primarily of selectivity estimation and cost modeling. We have implemented a new cost model for YugabyteDB which improves the accuracy of the CBO. This can be enabled as follows,

[gauravk-in]

These statistics are essential for estimating the costs of various query plans accurately.

can be

These statistics are essential for estimating the selectivity of filters and costs of various query plans accurately.

[gauravk-in]

To estimate the cost of fetching a tuple from DocDB, factors such as the number of SST files that may need to be read, and the estimated number of seeks, previous, and next operations that may be executed in the LSM subsystem, are taken into account.

can be

To estimate the cost of fetching a tuple from DocDB, we take into account factors such as the number of SST files that may need to be read, and the estimated number of seeks, previous, and next operations that may be executed in the LSM subsystem.

[ddhodge]

To estimate the cost of fetching a tuple from DocDB, we take into account factors such as the number of SST files that may need to be read, and the estimated number of seeks, previous, and next operations that may be executed in the LSM subsystem.

'we' - you mean the CBO? eg "the CBO takes into account..."

[ddhodge]

The query planner, also known as CBO comprises primarily of selectivity estimation and cost modeling. We have implemented a new cost model for YugabyteDB which improves the accuracy of the CBO. This can be enabled as follows,

Oh so the query planner and the CBO are the same?
How should we distinguish the new CBO from the old (PostgreSQL?) CBO?
What is 'selectivity estimation' and 'selectivity of filters'

[gauravk-in]

The query planner, also known as CBO comprises primarily of selectivity estimation and cost modeling. We have implemented a new cost model for YugabyteDB which improves the accuracy of the CBO. This can be enabled as follows,

Oh so the query planner and the CBO are the same? How should we distinguish the new CBO from the old (PostgreSQL?) CBO? What is 'selectivity estimation' and 'selectivity of filters'

• It may be better to remove the query planner and just use CBO. CBO maybe a part of the query planner which also includes the RBO (Rules Based Optimizer).
• The old one was also technically a cost based optimizer, it was just not accurately modeling the execution pipeline. We can call it heuristics based optimizer, because we were assigning some heuristic costs to the number of result rows depending on the type of the scan.
• Selectivity of a filter tells the number of rows that the filter will select, or the number of rows that will pass the filter.