pgsql: Optimize update of tables with generated columns

Optimize update of tables with generated columns

When updating a table row with generated columns, only recompute those
generated columns whose base columns have changed in this update and
keep the rest unchanged. This can result in a significant performance
benefit. The required information was already kept in
RangeTblEntry.extraUpdatedCols; we just have to make use of it.

Reviewed-by: Pavel Stehule <pavel(dot)stehule(at)gmail(dot)com>
Discussion: https://www.postgresql.org/message-id/flat/b05e781a-fa16-6b52-6738-761181204567(at)2ndquadrant(dot)com

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/c6679e4fca21d253ced84c51ac1a31c1b2aec72f

Modified Files
--------------
src/backend/commands/copy.c | 2 +-
src/backend/executor/execReplication.c | 4 ++--
src/backend/executor/nodeModifyTable.c | 37 ++++++++++++++++++++++++++++------
src/include/executor/nodeModifyTable.h | 2 +-
src/include/nodes/execnodes.h | 3 +++
5 files changed, 38 insertions(+), 10 deletions(-)