[Datafusion] Optimize literal expression evaluation #106
Description
Note: migrated from original JIRA: https://issues.apache.org/jira/browse/ARROW-10243
While benchmarking the tpch query I noticed that the physical literal expression takes up a sizable amount of time. I think the creation of the corresponding array for numeric literals can be speed up by creating Buffer and ArrayData directly without going through a builder. That also allows to skip building a null bitmap for non-null literals.
I'm also thinking whether it might be possible to cache the created array. For queries without a WHERE clause, I'd expect all batches except the last to have the same length. I'm not sure though where to store the cached value.
Another possible optimization could be to cast literals already on the logical plan side. In the tpch query the literal 1 is of type u64 in the logical plan and then needs to be processed by a cast kernel to convert to f64 for usage in an arithmetic expression.
The attached flamegraph is of 10 runs of tpch, with the data being loaded into memory before running the queries (See ARROW-10240).
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flamegraph ./target/release/tpch --iterations 10 --path ../tpch-dbgen --format tbl --query 1 --batch-size 4096 -c1 --load
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