e6336b8b57
Keep a pre-initialized FunctionCallInfoData in AggStatePerAggData, and re-use that at each row instead of doing InitFunctionCallInfoData each time. This saves only half a dozen assignments and maybe some stack manipulation, and yet that seems to be good for a percent or two of the overall query run time for simple aggregates such as count(*). The cost is that the FunctionCallInfoData (which is about a kilobyte, on 64-bit machines) stays allocated for the duration of the query instead of being short-lived stack data. But we're already paying an equivalent space cost for each regular FuncExpr or OpExpr node, so I don't feel bad about paying it for aggregate functions. The code seems a little cleaner this way too, since the number of things passed to advance_transition_function decreases.
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