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| author | Tom Lane <tgl@sss.pgh.pa.us> | 2022-07-09 15:10:15 -0400 |
|---|---|---|
| committer | Tom Lane <tgl@sss.pgh.pa.us> | 2022-07-09 15:10:15 -0400 |
| commit | 3cd0ac987819280eb8dd3e0997f0294b8bc6355a (patch) | |
| tree | adcb32ec90bca7d80e16bbd4e2cbf2d4242d4a85 /src/include/nodes | |
| parent | 8c73c11a0d39049de2c1f400d8765a0eb21f5228 (diff) | |
| download | postgresql-3cd0ac987819280eb8dd3e0997f0294b8bc6355a.tar.gz postgresql-3cd0ac987819280eb8dd3e0997f0294b8bc6355a.zip | |
Doc: rearrange high-level commentary about node support coverage.
copyfuncs.c and friends no longer seem like great places to put
high-level remarks about what's covered and what isn't. Move that
material to backend/nodes/README and other more-prominent places.
Add back (versions of) some remarks that disappeared in 2be87f092.
Discussion: https://postgr.es/m/3843645.1657385930@sss.pgh.pa.us
Diffstat (limited to 'src/include/nodes')
| -rw-r--r-- | src/include/nodes/execnodes.h | 21 |
1 files changed, 15 insertions, 6 deletions
diff --git a/src/include/nodes/execnodes.h b/src/include/nodes/execnodes.h index 967604b8a50..01b1727fc09 100644 --- a/src/include/nodes/execnodes.h +++ b/src/include/nodes/execnodes.h @@ -3,11 +3,20 @@ * execnodes.h * definitions for executor state nodes * - * ExprState represents the evaluation state for a whole expression tree. - * Most Expr-based plan nodes do not have a corresponding expression state - * node, they're fully handled within execExpr* - but sometimes the state - * needs to be shared with other parts of the executor, as for example - * with SubPlanState, which nodeSubplan.c has to modify. + * Most plan node types declared in plannodes.h have a corresponding + * execution-state node type declared here. An exception is that + * expression nodes (subtypes of Expr) are usually represented by steps + * of an ExprState, and fully handled within execExpr* - but sometimes + * their state needs to be shared with other parts of the executor, as + * for example with SubPlanState, which nodeSubplan.c has to modify. + * + * Node types declared in this file do not have any copy/equal/out/read + * support. (That is currently hard-wired in gen_node_support.pl, rather + * than being explicitly represented by pg_node_attr decorations here.) + * There is no need for copy, equal, or read support for executor trees. + * Output support could be useful for debugging; but there are a lot of + * specialized fields that would require custom code, so for now it's + * not provided. * * * Portions Copyright (c) 1996-2022, PostgreSQL Global Development Group @@ -53,7 +62,7 @@ struct LogicalTapeSet; /* ---------------- * ExprState node * - * ExprState is the top-level node for expression evaluation. + * ExprState represents the evaluation state for a whole expression tree. * It contains instructions (in ->steps) to evaluate the expression. * ---------------- */ |