pgsql: Revise child-to-root tuple conversion map management.

Revise child-to-root tuple conversion map management.

Store the tuple conversion map to convert a tuple from a child table's
format to the root format in a new ri_ChildToRootMap field in
ResultRelInfo. It is initialized if transition tuple capture for FOR
STATEMENT triggers or INSERT tuple routing on a partitioned table is
needed. Previously, ModifyTable kept the maps in the per-subplan
ModifyTableState->mt_per_subplan_tupconv_maps array, or when tuple
routing was used, in
ResultRelInfo->ri_Partitioninfo->pi_PartitionToRootMap. The new field
replaces both of those.

Now that the child-to-root tuple conversion map is always available in
ResultRelInfo (when needed), remove the TransitionCaptureState.tcs_map
field. The callers of Exec*Trigger() functions no longer need to set or
save it, which is much less confusing and bug-prone. Also, as a future
optimization, this will allow us to delay creating the map for a given
result relation until the relation is actually processed during
execution.

Author: Amit Langote
Discussion: https://www.postgresql.org/message-id/CA%2BHiwqHtCWLdK-LO%3DNEsvOdHx%2B7yv4mE_zYK0i3BH7dXb-wxog%40mail.gmail.com

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/6973533650c04653d9018f61c1ac99ecb11094bd

Modified Files
--------------
src/backend/commands/copy.c | 29 +----
src/backend/commands/trigger.c | 10 +-
src/backend/executor/execMain.c | 1 +
src/backend/executor/execPartition.c | 23 ++--
src/backend/executor/nodeModifyTable.c | 210 +++++++++------------------------
src/include/commands/trigger.h | 10 +-
src/include/executor/execPartition.h | 6 -
src/include/nodes/execnodes.h | 10 +-
8 files changed, 84 insertions(+), 215 deletions(-)