Re: Revised Patch to allow multiple table locks in "Unison" - Mailing list pgsql-patches

Tom Lane wrote:
>
> Bruce Momjian <pgman@candle.pha.pa.us> writes:
> > Patch applied.
>
> Idly looking this over again, I noticed a big OOPS:
>
> >> !            freeList(lockstmt->rellist);
>
> >> !            pfree(relname);
>
> >> !                    pfree(relname);
>
> It is most definitely NOT the executor's business to release pieces of
> the querytree; this will certainly break plpgsql functions, for example,
> where the same querytree is executed repeatedly.

Thanks for having a look, Tom. I've taken you advice into account, and
I've reworked the patch.

A new patch is below.

Neil

--
Neil Padgett
Red Hat Canada Ltd.                       E-Mail:  npadgett@redhat.com
2323 Yonge Street, Suite #300,
Toronto, ON  M4P 2C9

Index: doc/src/sgml/ref/lock.sgml
===================================================================
RCS file:
/home/projects/pgsql/cvsroot/pgsql/doc/src/sgml/ref/lock.sgml,v
retrieving revision 1.26
diff -c -p -r1.26 lock.sgml
*** doc/src/sgml/ref/lock.sgml    2001/08/04 22:01:38    1.26
--- doc/src/sgml/ref/lock.sgml    2001/08/07 18:34:23
*************** Postgres documentation
*** 15,21 ****
     LOCK
    </refname>
    <refpurpose>
!    Explicitly lock a table inside a transaction
    </refpurpose>
   </refnamediv>
   <refsynopsisdiv>
--- 15,21 ----
     LOCK
    </refname>
    <refpurpose>
!    Explicitly lock a table / tables inside a transaction
    </refpurpose>
   </refnamediv>
   <refsynopsisdiv>
*************** Postgres documentation
*** 23,30 ****
     <date>2001-07-09</date>
    </refsynopsisdivinfo>
    <synopsis>
! LOCK [ TABLE ] <replaceable class="PARAMETER">name</replaceable>
! LOCK [ TABLE ] <replaceable class="PARAMETER">name</replaceable> IN
<replaceable class="PARAMETER">lockmode</replaceable> MODE

  where <replaceable class="PARAMETER">lockmode</replaceable> is one of:

--- 23,30 ----
     <date>2001-07-09</date>
    </refsynopsisdivinfo>
    <synopsis>
! LOCK [ TABLE ] <replaceable class="PARAMETER">name</replaceable> [,
...]
! LOCK [ TABLE ] <replaceable class="PARAMETER">name</replaceable> [,
...] IN <replaceable class="PARAMETER">lockmode</replaceable> MODE

  where <replaceable class="PARAMETER">lockmode</replaceable> is one of:

*************** ERROR <replaceable class="PARAMETER">nam
*** 373,378 ****
--- 373,379 ----
       An example for this rule was given previously when discussing the
       use of SHARE ROW EXCLUSIVE mode rather than SHARE mode.
      </para>
+
     </listitem>
    </itemizedlist>

*************** ERROR <replaceable class="PARAMETER">nam
*** 383,388 ****
--- 384,395 ----
     </para>
    </note>

+   <para>
+    When locking multiple tables, the command LOCK a, b; is equivalent
to LOCK
+    a; LOCK b;. The tables are locked one-by-one in the order specified
in the
+    <command>LOCK</command> command.
+   </para>
+
    <refsect2 id="R2-SQL-LOCK-3">
     <refsect2info>
      <date>1999-06-08</date>
*************** ERROR <replaceable class="PARAMETER">nam
*** 406,411 ****
--- 413,419 ----
     <para>
      <command>LOCK</command> works only inside transactions.
     </para>
+
    </refsect2>
   </refsect1>

Index: src/backend/commands/command.c
===================================================================
RCS file:
/home/projects/pgsql/cvsroot/pgsql/src/backend/commands/command.c,v
retrieving revision 1.138
diff -c -p -r1.138 command.c
*** src/backend/commands/command.c    2001/08/04 22:01:38    1.138
--- src/backend/commands/command.c    2001/08/07 18:34:24
*************** needs_toast_table(Relation rel)
*** 1984,1991 ****
          MAXALIGN(data_length);
      return (tuple_length > TOAST_TUPLE_THRESHOLD);
  }
!
!
  /*
   *
   * LOCK TABLE
--- 1984,1990 ----
          MAXALIGN(data_length);
      return (tuple_length > TOAST_TUPLE_THRESHOLD);
  }
!
  /*
   *
   * LOCK TABLE
*************** needs_toast_table(Relation rel)
*** 1994,2019 ****
  void
  LockTableCommand(LockStmt *lockstmt)
  {
!     Relation    rel;
!     int            aclresult;
!
!     rel = heap_openr(lockstmt->relname, NoLock);
!
!     if (rel->rd_rel->relkind != RELKIND_RELATION)
!         elog(ERROR, "LOCK TABLE: %s is not a table", lockstmt->relname);
!
!     if (lockstmt->mode == AccessShareLock)
!         aclresult = pg_aclcheck(lockstmt->relname, GetUserId(), ACL_SELECT);
!     else
!         aclresult = pg_aclcheck(lockstmt->relname, GetUserId(),
!                                 ACL_UPDATE | ACL_DELETE);
!
!     if (aclresult != ACLCHECK_OK)
!         elog(ERROR, "LOCK TABLE: permission denied");
!
!     LockRelation(rel, lockstmt->mode);
!
!     heap_close(rel, NoLock);    /* close rel, keep lock */
  }


--- 1993,2030 ----
  void
  LockTableCommand(LockStmt *lockstmt)
  {
!     List *p;
!     Relation rel;
!
!     /* Iterate over the list and open, lock, and close the relations
!        one at a time
!      */
!
!         foreach(p, lockstmt->rellist)
!         {
!             char* relname = strVal(lfirst(p));
!             int            aclresult;
!
!             rel = heap_openr(relname, NoLock);
!
!             if (rel->rd_rel->relkind != RELKIND_RELATION)
!                 elog(ERROR, "LOCK TABLE: %s is not a table",
!                      relname);
!
!             if (lockstmt->mode == AccessShareLock)
!                 aclresult = pg_aclcheck(relname, GetUserId(),
!                                         ACL_SELECT);
!             else
!                 aclresult = pg_aclcheck(relname, GetUserId(),
!                                         ACL_UPDATE | ACL_DELETE);
!
!             if (aclresult != ACLCHECK_OK)
!                 elog(ERROR, "LOCK TABLE: permission denied");
!
!             LockRelation(rel, lockstmt->mode);
!
!             heap_close(rel, NoLock);    /* close rel, keep lock */
!         }
  }


Index: src/backend/nodes/copyfuncs.c
===================================================================
RCS file:
/home/projects/pgsql/cvsroot/pgsql/src/backend/nodes/copyfuncs.c,v
retrieving revision 1.150
diff -c -p -r1.150 copyfuncs.c
*** src/backend/nodes/copyfuncs.c    2001/08/04 22:01:38    1.150
--- src/backend/nodes/copyfuncs.c    2001/08/07 18:34:24
*************** _copyLockStmt(LockStmt *from)
*** 2425,2432 ****
  {
      LockStmt   *newnode = makeNode(LockStmt);

!     if (from->relname)
!         newnode->relname = pstrdup(from->relname);
      newnode->mode = from->mode;

      return newnode;
--- 2425,2432 ----
  {
      LockStmt   *newnode = makeNode(LockStmt);

!     Node_Copy(from, newnode, rellist);
!
      newnode->mode = from->mode;

      return newnode;
Index: src/backend/nodes/equalfuncs.c
===================================================================
RCS file:
/home/projects/pgsql/cvsroot/pgsql/src/backend/nodes/equalfuncs.c,v
retrieving revision 1.98
diff -c -p -r1.98 equalfuncs.c
*** src/backend/nodes/equalfuncs.c    2001/08/04 22:01:38    1.98
--- src/backend/nodes/equalfuncs.c    2001/08/07 18:34:24
*************** _equalDropUserStmt(DropUserStmt *a, Drop
*** 1283,1289 ****
  static bool
  _equalLockStmt(LockStmt *a, LockStmt *b)
  {
!     if (!equalstr(a->relname, b->relname))
          return false;
      if (a->mode != b->mode)
          return false;
--- 1283,1289 ----
  static bool
  _equalLockStmt(LockStmt *a, LockStmt *b)
  {
!     if (!equal(a->rellist, b->rellist))
          return false;
      if (a->mode != b->mode)
          return false;
Index: src/backend/parser/gram.y
===================================================================
RCS file: /home/projects/pgsql/cvsroot/pgsql/src/backend/parser/gram.y,v
retrieving revision 2.241
diff -c -p -r2.241 gram.y
*** src/backend/parser/gram.y    2001/08/06 05:42:48    2.241
--- src/backend/parser/gram.y    2001/08/07 18:34:30
*************** DeleteStmt:  DELETE FROM relation_expr w
*** 3281,3291 ****
                  }
          ;

! LockStmt:    LOCK_P opt_table relation_name opt_lock
                  {
                      LockStmt *n = makeNode(LockStmt);

!                     n->relname = $3;
                      n->mode = $4;
                      $$ = (Node *)n;
                  }
--- 3281,3291 ----
                  }
          ;

! LockStmt:    LOCK_P opt_table relation_name_list opt_lock
                  {
                      LockStmt *n = makeNode(LockStmt);

!                     n->rellist = $3;
                      n->mode = $4;
                      $$ = (Node *)n;
                  }
Index: src/include/nodes/parsenodes.h
===================================================================
RCS file:
/home/projects/pgsql/cvsroot/pgsql/src/include/nodes/parsenodes.h,v
retrieving revision 1.138
diff -c -p -r1.138 parsenodes.h
*** src/include/nodes/parsenodes.h    2001/08/04 22:01:39    1.138
--- src/include/nodes/parsenodes.h    2001/08/07 18:34:30
*************** typedef struct VariableResetStmt
*** 760,766 ****
  typedef struct LockStmt
  {
      NodeTag        type;
!     char       *relname;        /* relation to lock */
      int            mode;            /* lock mode */
  } LockStmt;

--- 760,766 ----
  typedef struct LockStmt
  {
      NodeTag        type;
!     List       *rellist;        /* relations to lock */
      int            mode;            /* lock mode */
  } LockStmt;

Index: src/interfaces/ecpg/preproc/preproc.y
===================================================================
RCS file:
/home/projects/pgsql/cvsroot/pgsql/src/interfaces/ecpg/preproc/preproc.y,v
retrieving revision 1.148
diff -c -p -r1.148 preproc.y
*** src/interfaces/ecpg/preproc/preproc.y    2001/08/04 22:01:39    1.148
--- src/interfaces/ecpg/preproc/preproc.y    2001/08/07 18:34:32
*************** DeleteStmt:  DELETE FROM relation_expr w
*** 2421,2427 ****
                  }
          ;

! LockStmt:  LOCK_P opt_table relation_name opt_lock
                  {
                      $$ = cat_str(4, make_str("lock"), $2, $3, $4);
                  }
--- 2421,2427 ----
                  }
          ;

! LockStmt:  LOCK_P opt_table relation_name_list opt_lock
                  {
                      $$ = cat_str(4, make_str("lock"), $2, $3, $4);
                  }