Track more precisely query locations for nested statements

Previously, a Query generated through the transform phase would have
unset stmt_location, tracking the starting point of a query string.

Extensions relying on the statement location to extract its relevant
parts in the source text string would fallback to use the whole
statement instead, leading to confusing results like in
pg_stat_statements for queries relying on nested queries, like:
- EXPLAIN, with top-level and nested query using the same query string,
and a query ID coming from the nested query when the non-top-level
entry.
- Multi-statements, with only partial portions of queries being
normalized.
- COPY TO with a query, SELECT or DMLs.

This patch improves things by keeping track of the statement locations
and propagate it to Query during transform, allowing PGSS to only show
the relevant part of the query for nested query.  This leads to less
bloat in entries for non-top-level entries, as queries can now be
grouped within the same (toplevel, queryid) duos in pg_stat_statements.
The result gives a stricter one-one mapping between query IDs and its
query strings.

The regression tests introduced in 45e0ba30fc40 produce differences
reflecting the new logic.

Author: Anthonin Bonnefoy
Reviewed-by: Michael Paquier, Jian He
Discussion: https://postgr.es/m/CAO6_XqqM6S9bQ2qd=75W+yKATwoazxSNhv5sjW06fjGAtHbTUA@mail.gmail.com

1 files changed, 10 insertions, 0 deletions

diff --git a/src/include/nodes/parsenodes.h b/src/include/nodes/parsenodes.h
index c92cef3d16d..b40b661ec8a 100644
--- a/src/include/nodes/parsenodes.h
+++ b/src/include/nodes/parsenodes.h
@@ -2046,6 +2046,8 @@ typedef struct InsertStmt
 	List	   *returningList;	/* list of expressions to return */
 	WithClause *withClause;		/* WITH clause */
 	OverridingKind override;	/* OVERRIDING clause */
+	ParseLoc	stmt_location;	/* start location, or -1 if unknown */
+	ParseLoc	stmt_len;		/* length in bytes; 0 means "rest of string" */
 } InsertStmt;
 
 /* ----------------------
@@ -2060,6 +2062,8 @@ typedef struct DeleteStmt
 	Node	   *whereClause;	/* qualifications */
 	List	   *returningList;	/* list of expressions to return */
 	WithClause *withClause;		/* WITH clause */
+	ParseLoc	stmt_location;	/* start location, or -1 if unknown */
+	ParseLoc	stmt_len;		/* length in bytes; 0 means "rest of string" */
 } DeleteStmt;
 
 /* ----------------------
@@ -2075,6 +2079,8 @@ typedef struct UpdateStmt
 	List	   *fromClause;		/* optional from clause for more tables */
 	List	   *returningList;	/* list of expressions to return */
 	WithClause *withClause;		/* WITH clause */
+	ParseLoc	stmt_location;	/* start location, or -1 if unknown */
+	ParseLoc	stmt_len;		/* length in bytes; 0 means "rest of string" */
 } UpdateStmt;
 
 /* ----------------------
@@ -2090,6 +2096,8 @@ typedef struct MergeStmt
 	List	   *mergeWhenClauses;	/* list of MergeWhenClause(es) */
 	List	   *returningList;	/* list of expressions to return */
 	WithClause *withClause;		/* WITH clause */
+	ParseLoc	stmt_location;	/* start location, or -1 if unknown */
+	ParseLoc	stmt_len;		/* length in bytes; 0 means "rest of string" */
 } MergeStmt;
 
 /* ----------------------
@@ -2159,6 +2167,8 @@ typedef struct SelectStmt
 	bool		all;			/* ALL specified? */
 	struct SelectStmt *larg;	/* left child */
 	struct SelectStmt *rarg;	/* right child */
+	ParseLoc	stmt_location;	/* start location, or -1 if unknown */
+	ParseLoc	stmt_len;		/* length in bytes; 0 means "rest of string" */
 	/* Eventually add fields for CORRESPONDING spec here */
 } SelectStmt;