On Sun, 8 Jan 2017 20:57:50 +0300
Victor Wagner <vi...@wagner.pp.ru> wrote:
> Collegues!
>
> Recently I've found out that PL/Python have very nice feature -
> explicit subtransaction object, which allows to execute block of code
> in the context of subtransaction.
>
[skip]
>
> I'm attaching the patch which implements subtransaction command for
Sorry, unfortunately attached empty file instead of patch
--
Victor Wagner <vi...@wagner.pp.ru>
diff --git a/doc/src/sgml/pltcl.sgml b/doc/src/sgml/pltcl.sgml
index 8afaf4a..7a532b7 100644
--- a/doc/src/sgml/pltcl.sgml
+++ b/doc/src/sgml/pltcl.sgml
@@ -901,6 +901,85 @@ if {[catch { spi_exec $sql_command }]} {
is a global variable.)
</para>
</sect1>
+ <sect1 id="pltcl-subransaction">
+ <title>Explicit Subtransactions</title>
+ <para>
+ Recovering from errors caused by database access as described in
+ <xref linkend="pltcl-error-handling"> can lead to an undesirable
+ situation where some operations succeed before one of them fails,
+ and after recovering from that error the data is left in an
+ inconsistent state. PL/Tcl offers a solution to this problem in
+ the form of explicit subtransactions.
+ </para>
+
+ <sect2>
+ <title>Subtransaction command</title>
+
+ <para>
+ Consider a function that implements a transfer between two
+ accounts:
+<programlisting>
+CREATE FUNCTION transfer_funds() RETURNS void AS $$
+if [catch {
+ spi_exec "UPDATE accounts SET balance = balance - 100 WHERE account_name = 'joe'"
+ spi_exec "UPDATE accounts SET balance = balance + 100 WHERE account_name = 'mary'"
+} errormsg] {
+ set result [format "error transferring funds: %s" $errormsg ]
+} else {
+ set result "funds transferred correctly"
+}
+set plan [spi_prepare "INSERT INTO operations (result) VALUES ($1)"]
+spi_execp -count 1 $plan, [list $result)
+$$ LANGUAGE pltclu;
+</programlisting>
+ If the second <literal>UPDATE</literal> statement results in an
+ exception being raised, this function will report the error, but
+ the result of the first <literal>UPDATE</literal> will
+ nevertheless be committed. In other words, the funds will be
+ withdrawn from Joe's account, but will not be transferred to
+ Mary's account.
+ </para>
+
+ <para>
+ To avoid such issues, you can wrap your
+ <literal>spi_exec</literal> calls in an explicit
+ subtransaction. The PL/Tcl provides a
+ commmand <literal>subtransaction</literal> to manage explicit
+ subtransactions.
+ Using explicit subtransactions
+ we can rewrite our function as:
+<programlisting>
+CREATE FUNCTION transfer_funds2() RETURNS void AS $$
+if [catch {
+ subtransaction {
+ spi_exec "UPDATE accounts SET balance = balance - 100 WHERE account_name = 'joe'"
+ spi_exec "UPDATE accounts SET balance = balance + 100 WHERE account_name = 'mary'"
+ }
+ } errormsg] {
+ set result [format "error transferring funds: %s" $errormsg]
+ } else {
+ set result "funds transferred correctly"
+ }
+ set plan [spi_prepare "INSERT INTO operations (result) VALUES ($1)"]
+ spi_execp $plan, [list $result]
+$$ LANGUAGE pltclu;
+</programlisting>
+ Note that the use of <literal>catch</literal> is still
+ required. Otherwise the exception would propagate to the top of
+ the stack and would cause the whole function to abort with
+ a <productname>PostgreSQL</productname> error, so that the
+ <literal>operations</literal> table would not have any row
+ inserted into it. The <literal>subtransaction</literal> command does not
+ trap errors, it only assures that all database operations executed
+ inside its scope will be atomically committed or rolled back. A
+ rollback of the subtransaction block occurs on any kind of
+ exception exit, not only ones caused by errors originating from
+ database access. A regular Tcl exception raised inside an
+ explicit subtransaction block would also cause the subtransaction
+ to be rolled back.
+ </para>
+ </sect2>
+ </sect1>
<sect1 id="pltcl-unknown">
<title>Modules and the <function>unknown</> Command</title>
diff --git a/src/pl/tcl/Makefile b/src/pl/tcl/Makefile
index 25082ec..614385d 100644
--- a/src/pl/tcl/Makefile
+++ b/src/pl/tcl/Makefile
@@ -28,7 +28,7 @@ DATA = pltcl.control pltcl--1.0.sql pltcl--unpackaged--1.0.sql \
pltclu.control pltclu--1.0.sql pltclu--unpackaged--1.0.sql
REGRESS_OPTS = --dbname=$(PL_TESTDB) --load-extension=pltcl
-REGRESS = pltcl_setup pltcl_queries pltcl_unicode
+REGRESS = pltcl_setup pltcl_queries pltcl_unicode pltcl_subxact
# Tcl on win32 ships with import libraries only for Microsoft Visual C++,
# which are not compatible with mingw gcc. Therefore we need to build a
diff --git a/src/pl/tcl/expected/pltcl_subxact.out b/src/pl/tcl/expected/pltcl_subxact.out
new file mode 100644
index 0000000..17b9d90
--- /dev/null
+++ b/src/pl/tcl/expected/pltcl_subxact.out
@@ -0,0 +1,145 @@
+--
+-- Test explicit subtransactions
+--
+-- Test table to see if transactions get properly rolled back
+CREATE TABLE subtransaction_tbl (
+ i integer
+);
+CREATE FUNCTION subtransaction_ctx_test(what_error text = NULL) RETURNS text
+AS $$
+subtransaction {
+ spi_exec "INSERT INTO subtransaction_tbl VALUES (1)"
+ spi_exec "INSERT INTO subtransaction_tbl VALUES (2)"
+ if {$1 == "SPI"} {
+ spi_exec "INSERT INTO subtransaction_tbl VALUES ('oops')"
+ } elseif { $1 == "Tcl"} {
+ elog ERROR "Tcl error"
+ }
+}
+$$ LANGUAGE pltcl;
+SELECT subtransaction_ctx_test();
+ subtransaction_ctx_test
+-------------------------
+
+(1 row)
+
+SELECT * FROM subtransaction_tbl;
+ i
+---
+ 1
+ 2
+(2 rows)
+
+TRUNCATE subtransaction_tbl;
+SELECT subtransaction_ctx_test('SPI');
+ERROR: invalid input syntax for integer: "oops"
+CONTEXT: invalid input syntax for integer: "oops"
+ while executing
+"spi_exec "INSERT INTO subtransaction_tbl VALUES ('oops')""
+ invoked from within
+"subtransaction {
+ spi_exec "INSERT INTO subtransaction_tbl VALUES (1)"
+ spi_exec "INSERT INTO subtransaction_tbl VALUES (2)"
+ if {$1 == "SPI"..."
+ (procedure "__PLTcl_proc_16494" line 3)
+ invoked from within
+"__PLTcl_proc_16494 SPI"
+in PL/Tcl function "subtransaction_ctx_test"
+SELECT * FROM subtransaction_tbl;
+ i
+---
+(0 rows)
+
+TRUNCATE subtransaction_tbl;
+SELECT subtransaction_ctx_test('Tcl');
+ERROR: Tcl error
+CONTEXT: Tcl error
+ while executing
+"elog ERROR "Tcl error""
+ invoked from within
+"subtransaction {
+ spi_exec "INSERT INTO subtransaction_tbl VALUES (1)"
+ spi_exec "INSERT INTO subtransaction_tbl VALUES (2)"
+ if {$1 == "SPI"..."
+ (procedure "__PLTcl_proc_16494" line 3)
+ invoked from within
+"__PLTcl_proc_16494 Tcl"
+in PL/Tcl function "subtransaction_ctx_test"
+SELECT * FROM subtransaction_tbl;
+ i
+---
+(0 rows)
+
+TRUNCATE subtransaction_tbl;
+-- Nested subtransactions
+CREATE FUNCTION subtransaction_nested_test(swallow boolean = 'f') RETURNS text
+AS $$
+elog NOTICE "subtransaction_tested_test got arg '$1'"
+spi_exec "INSERT INTO subtransaction_tbl VALUES (1)"
+subtransaction {
+ spi_exec "INSERT INTO subtransaction_tbl VALUES (2)"
+ if [catch {
+ subtransaction {
+ spi_exec "INSERT INTO subtransaction_tbl VALUES (3)"
+ spi_exec "error"
+ }
+ } errormsg] {
+ if {$1 != "t"} {
+ error $errormsg $::errorInfo $::errorCode
+ }
+ elog NOTICE "Swallowed $errormsg"
+ }
+}
+return "ok"
+$$ LANGUAGE pltcl;
+SELECT subtransaction_nested_test();
+NOTICE: subtransaction_tested_test got arg 'f'
+ERROR: syntax error at or near "error"
+CONTEXT: syntax error at or near "error"
+ while executing
+"spi_exec "error""
+ invoked from within
+"subtransaction {
+ spi_exec "INSERT INTO subtransaction_tbl VALUES (3)"
+ spi_exec "error"
+ }"
+ invoked from within
+"if [catch {
+ subtransaction {
+ spi_exec "INSERT INTO subtransaction_tbl VALUES (3)"
+ spi_exec "error"
+ }
+ } errormsg] {
+..."
+ invoked from within
+"subtransaction {
+ spi_exec "INSERT INTO subtransaction_tbl VALUES (2)"
+ if [catch {
+ subtransaction {
+ spi_exec "INSERT INTO subt..."
+ (procedure "__PLTcl_proc_16498" line 5)
+ invoked from within
+"__PLTcl_proc_16498 f"
+in PL/Tcl function "subtransaction_nested_test"
+SELECT * FROM subtransaction_tbl;
+ i
+---
+(0 rows)
+
+TRUNCATE subtransaction_tbl;
+SELECT subtransaction_nested_test('t');
+NOTICE: subtransaction_tested_test got arg 't'
+NOTICE: Swallowed syntax error at or near "error"
+ subtransaction_nested_test
+----------------------------
+ ok
+(1 row)
+
+SELECT * FROM subtransaction_tbl;
+ i
+---
+ 1
+ 2
+(2 rows)
+
+TRUNCATE subtransaction_tbl;
diff --git a/src/pl/tcl/pltcl.c b/src/pl/tcl/pltcl.c
index d813dcb..f03ecf1 100644
--- a/src/pl/tcl/pltcl.c
+++ b/src/pl/tcl/pltcl.c
@@ -307,6 +307,8 @@ static HeapTuple pltcl_build_tuple_result(Tcl_Interp *interp,
pltcl_call_state *call_state);
static void pltcl_init_tuple_store(pltcl_call_state *call_state);
+static int pltcl_subtransaction(ClientData cdata, Tcl_Interp *interp,
+ int objc, Tcl_Obj *const objv[]);
/*
* Hack to override Tcl's builtin Notifier subsystem. This prevents the
@@ -483,7 +485,8 @@ pltcl_init_interp(pltcl_interp_desc *interp_desc, bool pltrusted)
pltcl_SPI_execute_plan, NULL, NULL);
Tcl_CreateObjCommand(interp, "spi_lastoid",
pltcl_SPI_lastoid, NULL, NULL);
-
+ Tcl_CreateObjCommand(interp, "subtransaction",
+ pltcl_subtransaction, NULL,NULL);
/************************************************************
* Try to load the unknown procedure from pltcl_modules
************************************************************/
@@ -3070,3 +3073,43 @@ pltcl_init_tuple_store(pltcl_call_state *call_state)
CurrentResourceOwner = oldowner;
MemoryContextSwitchTo(oldcxt);
}
+
+/*
+ * pltcl_subtransaction - implements tcl level subtransaction block
+ * Called with exactly one argument - piece of Tcl Code, and executes
+ * this code inside subtransaction.
+ * Rolls subtransaction back if Tcl_EvalEx returns TCL_ERROR
+ */
+static int
+pltcl_subtransaction(ClientData cdata, Tcl_Interp *interp,
+ int objc, Tcl_Obj *const objv[])
+{
+ /* Initialize local memory context */
+ MemoryContext oldcontext = CurrentMemoryContext;
+ ResourceOwner oldowner = CurrentResourceOwner;
+ int retcode;
+ if (objc != 2)
+ {
+ Tcl_WrongNumArgs(interp,1,objv,"command");
+ return TCL_ERROR;
+ }
+
+ BeginInternalSubTransaction(NULL);
+ MemoryContextSwitchTo(TopTransactionContext);
+
+ retcode = Tcl_EvalObjEx(interp, objv[1],0);
+
+ if (retcode == TCL_ERROR)
+ {
+ /* Roollback the subtransaction */
+ RollbackAndReleaseCurrentSubTransaction();
+ }
+ else
+ {
+ /* Commit the subtransaction */
+ ReleaseCurrentSubTransaction();
+ }
+ MemoryContextSwitchTo(oldcontext);
+ CurrentResourceOwner = oldowner;
+ return retcode;
+}
diff --git a/src/pl/tcl/sql/pltcl_subxact.sql b/src/pl/tcl/sql/pltcl_subxact.sql
new file mode 100644
index 0000000..c5859e1
--- /dev/null
+++ b/src/pl/tcl/sql/pltcl_subxact.sql
@@ -0,0 +1,63 @@
+--
+-- Test explicit subtransactions
+--
+
+-- Test table to see if transactions get properly rolled back
+
+CREATE TABLE subtransaction_tbl (
+ i integer
+);
+
+CREATE FUNCTION subtransaction_ctx_test(what_error text = NULL) RETURNS text
+AS $$
+subtransaction {
+ spi_exec "INSERT INTO subtransaction_tbl VALUES (1)"
+ spi_exec "INSERT INTO subtransaction_tbl VALUES (2)"
+ if {$1 == "SPI"} {
+ spi_exec "INSERT INTO subtransaction_tbl VALUES ('oops')"
+ } elseif { $1 == "Tcl"} {
+ elog ERROR "Tcl error"
+ }
+}
+$$ LANGUAGE pltcl;
+
+SELECT subtransaction_ctx_test();
+SELECT * FROM subtransaction_tbl;
+TRUNCATE subtransaction_tbl;
+SELECT subtransaction_ctx_test('SPI');
+SELECT * FROM subtransaction_tbl;
+TRUNCATE subtransaction_tbl;
+SELECT subtransaction_ctx_test('Tcl');
+SELECT * FROM subtransaction_tbl;
+TRUNCATE subtransaction_tbl;
+
+-- Nested subtransactions
+
+CREATE FUNCTION subtransaction_nested_test(swallow boolean = 'f') RETURNS text
+AS $$
+elog NOTICE "subtransaction_tested_test got arg '$1'"
+spi_exec "INSERT INTO subtransaction_tbl VALUES (1)"
+subtransaction {
+ spi_exec "INSERT INTO subtransaction_tbl VALUES (2)"
+ if [catch {
+ subtransaction {
+ spi_exec "INSERT INTO subtransaction_tbl VALUES (3)"
+ spi_exec "error"
+ }
+ } errormsg] {
+ if {$1 != "t"} {
+ error $errormsg $::errorInfo $::errorCode
+ }
+ elog NOTICE "Swallowed $errormsg"
+ }
+}
+return "ok"
+$$ LANGUAGE pltcl;
+
+SELECT subtransaction_nested_test();
+SELECT * FROM subtransaction_tbl;
+TRUNCATE subtransaction_tbl;
+
+SELECT subtransaction_nested_test('t');
+SELECT * FROM subtransaction_tbl;
+TRUNCATE subtransaction_tbl;
--
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