58a359e585
This adjusts slot_deform_heap_tuple() to add special-case loops to eliminate much of the branching that was done within the body of the main deform loop. Previously, while looping over each attribute to deform, slot_deform_heap_tuple() would always recheck if the given attribute was NULL by looking at HeapTupleHasNulls() and if so, went on to check the tuple's NULL bitmap. Since many tuples won't contain any NULLs, we can just check HeapTupleHasNulls() once and when there are no NULLs, use a more compact version of the deforming loop which contains no NULL checking code at all. The same is possible for the "slow" mode checking part of the loop. That variable was checked several times for each attribute, once to determine if the offset to the attribute value could be taken from the attcacheoff, and again to check if the offset could be cached for next time. These "slow" checks can mostly be eliminated by instead having multiple loops. Initially, we can start in the non-slow loop and break out of that loop if and only if we must stop caching the offset. This eliminates branching for both slow and non-slow deforming methods. The amount of code required for the no nulls / non-slow version is very small. It's possible to have separate loops like this due to the fact that once we move into slow mode, we never need to switch back into non-slow mode for a given tuple. We have the compiler take care of writing out the multiple required loops by having a pg_attribute_always_inline function which gets called various times passing in constant values for the "slow" and "hasnulls" parameters. This allows the compiler to eliminate const-false branches and remove comparisons for const-true ones. This commit has shown overall query performance increases of around 5-20% in deform-heavy OLAP-type workloads. Author: David Rowley Reviewed-by: Victor Yegorov Discussion: https://postgr.es/m/CAGnEbog92Og2CpC2S8=g_HozGsWtt_3kRS1sXjLz0jKSoCNfLw@mail.gmail.com Discussion: https://postgr.es/m/CAApHDvo9e0XG71WrefYaRv5n4xNPLK4k8LjD0mSR3c9KR2vi2Q@mail.gmail.com
PostgreSQL Database Management System
This directory contains the source code distribution of the PostgreSQL database management system.
PostgreSQL is an advanced object-relational database management system that supports an extended subset of the SQL standard, including transactions, foreign keys, subqueries, triggers, user-defined types and functions. This distribution also contains C language bindings.
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