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

I have backed out the entire patch.  I think it is best for the author
to make the suggested changes and resubmit.  Reversed patch attached.


> 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.
> Bruce, please remove those lines.
>
> Another thing I am concerned about now that I look more closely is that
> the multi-rel case code opens the relations without any lock, and then
> assumes they'll stick around while it opens and access-checks the rest.
> This will fail if someone else drops one of the rels meanwhile.  I think
> the entire routine should be reduced to a simple loop that opens, locks,
> and closes the rels one at a time.  The extra code bulk to do it this
> way isn't buying us anything at all.
>
>             regards, tom lane
>
> ---------------------------(end of broadcast)---------------------------
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>

--
  Bruce Momjian                        |  http://candle.pha.pa.us
  pgman@candle.pha.pa.us               |  (610) 853-3000
  +  If your life is a hard drive,     |  830 Blythe Avenue
  +  Christ can be your backup.        |  Drexel Hill, Pennsylvania 19026
Tom Lane wrote:
>
> Neil Padgett <npadgett@redhat.com> writes:
> >> This seems fine to me (and in fact I thought we'd already agreed to it).
>
> > Here's the patch then. =)
>
> [ quick mental checklist... ]  You forgot the documentation updates.
> Otherwise it looks good.

Ok -- I made a go at the documentation. I'm no SGML wizard, so if
someone could check my changes that would be helpful.

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 1.24
diff -c -p -r1.24 lock.sgml
*** doc/src/sgml/ref/lock.sgml    2001/07/09 22:18:33    1.24
--- doc/src/sgml/ref/lock.sgml    2001/08/02 21:39:42
*************** 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 1.136
diff -c -p -r1.136 command.c
*** src/backend/commands/command.c    2001/07/16 05:06:57    1.136
--- src/backend/commands/command.c    2001/08/02 21:39:43
*************** 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 */
  }


--- 1993,2096 ----
  void
  LockTableCommand(LockStmt *lockstmt)
  {
!     int         relCnt;
!
!     relCnt = length(lockstmt -> rellist);
!
!     /* Handle a single relation lock specially to avoid overhead on likely the
!        most common case */
!
!     if(relCnt == 1)
!     {
!
!         /* Locking a single table */
!
!         Relation    rel;
!         int            aclresult;
!         char *relname;
!
!         relname = strVal(lfirst(lockstmt->rellist));
!
!         freeList(lockstmt->rellist);
!
!         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);
!
!         pfree(relname);
!
!         heap_close(rel, NoLock);    /* close rel, keep lock */
!     }
!     else
!     {
!         List *p;
!         Relation *RelationArray;
!         Relation *pRel;
!
!         /* Locking multiple tables */
!
!         /* Create an array of relations */
!
!         RelationArray = palloc(relCnt * sizeof(Relation));
!         pRel = RelationArray;
!
!         /* Iterate over the list and populate the relation array */
!
!         foreach(p, lockstmt->rellist)
!         {
!             char* relname = strVal(lfirst(p));
!             int            aclresult;
!
!             *pRel = heap_openr(relname, NoLock);
!
!             if ((*pRel)->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");

!             pRel++;
!             pfree(relname);
!         }

!         /* Now, lock all the relations, closing each after it is locked
!            (Keeping the locks)
!          */

!         for(pRel = RelationArray;
!             pRel < RelationArray + relCnt;
!             pRel++)
!             {
!                 LockRelation(*pRel, lockstmt->mode);

!                 heap_close(*pRel, NoLock);
!             }

!         /* Free the relation array */

!         pfree(RelationArray);
!     }
  }


Index: src/backend/nodes/copyfuncs.c
===================================================================
RCS file:
/home/projects/pgsql/cvsroot/pgsql/src/backend/nodes/copyfuncs.c,v
retrieving revision 1.148
diff -c -p -r1.148 copyfuncs.c
*** src/backend/nodes/copyfuncs.c    2001/07/16 19:07:37    1.148
--- src/backend/nodes/copyfuncs.c    2001/08/02 21:39:44
*************** _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 1.96
diff -c -p -r1.96 equalfuncs.c
*** src/backend/nodes/equalfuncs.c    2001/07/16 19:07:38    1.96
--- src/backend/nodes/equalfuncs.c    2001/08/02 21:39:44
*************** _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 2.238
diff -c -p -r2.238 gram.y
*** src/backend/parser/gram.y    2001/07/16 19:07:40    2.238
--- src/backend/parser/gram.y    2001/08/02 21:39:46
*************** DeleteStmt:  DELETE FROM relation_expr w
*** 3280,3290 ****
                  }
          ;

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

!                     n->relname = $3;
                      n->mode = $4;
                      $$ = (Node *)n;
                  }
--- 3280,3290 ----
                  }
          ;

! 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 1.136
diff -c -p -r1.136 parsenodes.h
*** src/include/nodes/parsenodes.h    2001/07/16 19:07:40    1.136
--- src/include/nodes/parsenodes.h    2001/08/02 21:39:46
*************** 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 1.146
diff -c -p -r1.146 preproc.y
*** src/interfaces/ecpg/preproc/preproc.y    2001/07/16 05:07:00    1.146
--- src/interfaces/ecpg/preproc/preproc.y    2001/08/02 21:39:49
*************** 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);
                  }