Fix plpgsql's handling of "simple" expression evaluation.

In general, expression execution state trees aren't re-entrantly usable,
since functions can store private state information in them.
For efficiency reasons, plpgsql tries to cache and reuse state trees for
"simple" expressions.  It can get away with that most of the time, but it
can fail if the state tree is dirty from a previous failed execution (as
in an example from Alvaro) or is being used recursively (as noted by me).

Fix by tracking whether a state tree is in use, and falling back to the
"non-simple" code path if so.  This results in a pretty considerable speed
hit when the non-simple path is taken, but the available alternatives seem
even more unpleasant because they add overhead in the simple path.  Per
idea from Heikki.

Back-patch to all supported branches.

diff --git a/src/pl/plpgsql/src/pl_exec.c b/src/pl/plpgsql/src/pl_exec.c
index 2d1ede46be0c1c13720a2d412520335061ba31a0..526f9d789e5659146bf2e8f8d85013667742a1c4 100644 (file)
--- a/src/pl/plpgsql/src/pl_exec.c
+++ b/src/pl/plpgsql/src/pl_exec.c
@@ -3920,7 +3920,14 @@ exec_eval_expr(PLpgSQL_execstate *estate,
         * directly
         */
        if (expr->expr_simple_expr != NULL)
-               return exec_eval_simple_expr(estate, expr, isNull, rettype);
+       {
+               /*
+                * If expression is in use in current xact, don't touch it.
+                */
+               if (!(expr->expr_simple_in_use &&
+                         expr->expr_simple_id == estate->eval_estate_simple_id))
+                       return exec_eval_simple_expr(estate, expr, isNull, rettype);
+       }
 
        rc = exec_run_select(estate, expr, 2, NULL);
        if (rc != SPI_OK_SELECT)
@@ -4071,6 +4078,7 @@ exec_eval_simple_expr(PLpgSQL_execstate *estate,
        {
                expr->expr_simple_state = ExecPrepareExpr(expr->expr_simple_expr,
                                                                                                  estate->eval_estate);
+               expr->expr_simple_in_use = false;
                expr->expr_simple_id = estate->eval_estate_simple_id;
        }
 
@@ -4130,6 +4138,11 @@ exec_eval_simple_expr(PLpgSQL_execstate *estate,
                        ActiveSnapshot = CopySnapshot(GetTransactionSnapshot());
                }
 
+               /*
+                * Mark expression as busy for the duration of the ExecEvalExpr call.
+                */
+               expr->expr_simple_in_use = true;
+
                /*
                 * Finally we can call the executor to evaluate the expression
                 */
@@ -4137,11 +4150,15 @@ exec_eval_simple_expr(PLpgSQL_execstate *estate,
                                                          econtext,
                                                          isNull,
                                                          NULL);
+
+               /* Assorted cleanup */
+               expr->expr_simple_in_use = false;
                MemoryContextSwitchTo(oldcontext);
        }
        PG_CATCH();
        {
                /* Restore global vars and propagate error */
+               /* note we intentionally don't reset expr_simple_in_use here */
                ActiveSnapshot = saveActiveSnapshot;
                PG_RE_THROW();
        }
@@ -4741,6 +4758,7 @@ exec_simple_check_plan(PLpgSQL_expr *expr)
         */
        expr->expr_simple_expr = tle->expr;
        expr->expr_simple_state = NULL;
+       expr->expr_simple_in_use = false;
        expr->expr_simple_id = -1;
        /* Also stash away the expression result type */
        expr->expr_simple_type = exprType((Node *) tle->expr);

diff --git a/src/pl/plpgsql/src/plpgsql.h b/src/pl/plpgsql/src/plpgsql.h
index c48a66a1912c5b8ab779ce866298e2043037fa3d..12790e9aceb10cc0b564826afee4833d7992a5f0 100644 (file)
--- a/src/pl/plpgsql/src/plpgsql.h
+++ b/src/pl/plpgsql/src/plpgsql.h
@@ -181,10 +181,11 @@ typedef struct PLpgSQL_expr
 
        /*
         * if expr is simple AND prepared in current eval_estate,
-        * expr_simple_state is valid.  Test validity by seeing if expr_simple_id
-        * matches eval_estate_simple_id.
+        * expr_simple_state and expr_simple_in_use are valid. Test validity by
+        * seeing if expr_simple_id matches eval_estate_simple_id.
         */
-       ExprState  *expr_simple_state;
+       ExprState  *expr_simple_state;          /* eval tree for expr_simple_expr */
+       bool            expr_simple_in_use;             /* true if eval tree is active */
        long int        expr_simple_id;
 
        /* params to pass to expr */

diff --git a/src/test/regress/expected/plpgsql.out b/src/test/regress/expected/plpgsql.out
index f2826f10625b0f6d8a072e287a6ba01fd6f1b8df..ff1a9604df736a8f3281ae26a6d41cfdc1cae8dd 100644 (file)
--- a/src/test/regress/expected/plpgsql.out
+++ b/src/test/regress/expected/plpgsql.out
@@ -2977,3 +2977,50 @@ SELECT nonsimple_expr_test();
 (1 row)
 
 DROP FUNCTION nonsimple_expr_test();
+--
+-- Test cases involving recursion and error recovery in simple expressions
+-- (bugs in all versions before October 2010).  The problems are most
+-- easily exposed by mutual recursion between plpgsql and sql functions.
+--
+create function recurse(float8) returns float8 as
+$$
+begin
+  if ($1 < 10) then
+    return sql_recurse($1 + 1);
+  else
+    return $1;
+  end if;
+end;
+$$ language plpgsql;
+-- "limit" is to prevent this from being inlined
+create function sql_recurse(float8) returns float8 as
+$$ select recurse($1) limit 1; $$ language sql;
+select recurse(0);
+ recurse 
+---------
+      10
+(1 row)
+
+create function error1(text) returns text language sql as
+$$ SELECT relname::text FROM pg_class c WHERE c.oid = $1::regclass $$;
+create function error2(p_name_table text) returns text language plpgsql as $$
+begin
+  return error1(p_name_table);
+end$$;
+BEGIN;
+create table public.stuffs (stuff text);
+SAVEPOINT a;
+select error2('nonexistent.stuffs');
+ERROR:  schema "nonexistent" does not exist
+CONTEXT:  SQL function "error1" statement 1
+PL/pgSQL function "error2" line 2 at return
+ROLLBACK TO a;
+select error2('public.stuffs');
+ error2 
+--------
+ stuffs
+(1 row)
+
+rollback;
+drop function error2(p_name_table text);
+drop function error1(text);

diff --git a/src/test/regress/sql/plpgsql.sql b/src/test/regress/sql/plpgsql.sql
index 27ab5afbdffa0c49a374fca95ffec2530e804ddd..37bdb72fb7e8d17633ee318eb45368495d49c31f 100644 (file)
--- a/src/test/regress/sql/plpgsql.sql
+++ b/src/test/regress/sql/plpgsql.sql
@@ -2480,3 +2480,45 @@ $$ LANGUAGE plpgsql;
 SELECT nonsimple_expr_test();
 
 DROP FUNCTION nonsimple_expr_test();
+
+--
+-- Test cases involving recursion and error recovery in simple expressions
+-- (bugs in all versions before October 2010).  The problems are most
+-- easily exposed by mutual recursion between plpgsql and sql functions.
+--
+
+create function recurse(float8) returns float8 as
+$$
+begin
+  if ($1 < 10) then
+    return sql_recurse($1 + 1);
+  else
+    return $1;
+  end if;
+end;
+$$ language plpgsql;
+
+-- "limit" is to prevent this from being inlined
+create function sql_recurse(float8) returns float8 as
+$$ select recurse($1) limit 1; $$ language sql;
+
+select recurse(0);
+
+create function error1(text) returns text language sql as
+$$ SELECT relname::text FROM pg_class c WHERE c.oid = $1::regclass $$;
+
+create function error2(p_name_table text) returns text language plpgsql as $$
+begin
+  return error1(p_name_table);
+end$$;
+
+BEGIN;
+create table public.stuffs (stuff text);
+SAVEPOINT a;
+select error2('nonexistent.stuffs');
+ROLLBACK TO a;
+select error2('public.stuffs');
+rollback;
+
+drop function error2(p_name_table text);
+drop function error1(text);