patch for large queries

Hi Hackers,

I don't like last minute patches before the final freeze, but I believe that
this one could be useful for people experiencing out-of-memory crashes while
executing queries which retrieve or use a very large number of tuples.

The problem happens when storage is allocated for functions results used in
a large query, for example:

select upper(name) from big_table;
select big_table.array[1] from big_table;
select count(upper(name)) from big_table;

This patch is a dirty hack that fixes the out-of-memory problem for the most
common cases, like the above ones. It is not the final solution for the
problem but it can work for some people, so I'm posting it.

The patch should be safe because all changes are under #ifdef. Furthermore
the feature can be enabled or disabled at runtime by the `free_tuple_memory'
options in the pg_options file. The option is disabled by default and must
be explicitly enabled at runtime to have any effect.

To enable the patch add the follwing line to Makefile.custom:

CUSTOM_COPT += -DFREE_TUPLE_MEMORY

To enable the option at runtime add the following line to pg_option:

free_tuple_memory=1

Here is the patch:

*** src/include/utils/portal.h.orig Wed May 26 09:07:16 1999
--- src/include/utils/portal.h Fri Jun 11 18:06:07 1999
***************
*** 80,85 ****
--- 80,89 ----
extern PortalVariableMemory PortalGetVariableMemory(Portal portal);
extern PortalHeapMemory PortalGetHeapMemory(Portal portal);

+ #ifdef FREE_TUPLE_MEMORY
+ bool PortalHeapMemoryIsValid(MemoryContext context, Pointer pointer);
+ #endif
+
/* estimate of the maximum number of open portals a user would have,
* used in initially sizing the PortalHashTable in EnablePortalManager()
*/
*** src/backend/utils/mmgr/portalmem.c.orig Wed May 26 09:06:02 1999
--- src/backend/utils/mmgr/portalmem.c Fri Jun 11 18:06:28 1999
***************
*** 289,294 ****
--- 289,312 ----
}
}

+ #ifdef FREE_TUPLE_MEMORY
+ /*
+ * PortalHeapMemoryIsValid --
+ *
+ * Check if a pointer is allocated in a memory context.
+ *
+ */
+ bool
+ PortalHeapMemoryIsValid(MemoryContext context, Pointer pointer)
+ {
+ HeapMemoryBlock block = HEAPMEMBLOCK((PortalHeapMemory) context);
+
+ AssertState(PointerIsValid(block));
+
+ return (AllocSetContains(&block->setData, pointer));
+ }
+ #endif
+
/* ----------------
* PortalHeapMemoryRealloc
* ----------------
*** src/include/utils/trace.h.orig Sat Jun 5 09:00:40 1999
--- src/include/utils/trace.h Fri Jun 11 19:01:30 1999
***************
*** 64,69 ****
--- 64,72 ----
OPT_SYSLOG, /* use syslog for error messages */
OPT_HOSTLOOKUP, /* enable hostname lookup in ps_status */
OPT_SHOWPORTNUMBER, /* show port number in ps_status */
+ #ifdef FREE_TUPLE_MEMORY
+ OPT_FREE_TUPLE_MEMORY, /* try to pfree memory for each tuple */
+ #endif

NUM_PG_OPTIONS /* must be the last item of enum */
};
***************
*** 83,91 ****
#endif /* TRACE_H */

/*
! * Local variables:
! * tab-width: 4
! * c-indent-level: 4
! * c-basic-offset: 4
* End:
*/
--- 86,94 ----
#endif /* TRACE_H */

/*
! * Local Variables:
! * tab-width: 4
! * c-indent-level: 4
! * c-basic-offset: 4
* End:
*/
*** src/backend/utils/misc/trace.c.orig Sat Jun 5 09:00:37 1999
--- src/backend/utils/misc/trace.c Fri Jun 11 19:01:31 1999
***************
*** 73,78 ****
--- 73,81 ----
"syslog", /* use syslog for error messages */
"hostlookup", /* enable hostname lookup in ps_status */
"showportnumber", /* show port number in ps_status */
+ #ifdef FREE_TUPLE_MEMORY
+ "free_tuple_memory", /* try to pfree memory for each tuple */
+ #endif

/* NUM_PG_OPTIONS */ /* must be the last item of enum */
};
***************
*** 404,412 ****
}

/*
! * Local variables:
! * tab-width: 4
! * c-indent-level: 4
! * c-basic-offset: 4
* End:
*/
--- 407,415 ----
}

/*
! * Local Variables:
! * tab-width: 4
! * c-indent-level: 4
! * c-basic-offset: 4
* End:
*/
*** src/backend/access/common/heaptuple.c.orig Wed May 26 09:01:59 1999
--- src/backend/access/common/heaptuple.c Fri Jun 11 19:08:33 1999
***************
*** 27,32 ****
--- 27,37 ----
#include <storage/bufpage.h>
#include <utils/memutils.h>

+ #ifdef FREE_TUPLE_MEMORY
+ #include <utils/portal.h>
+ #include <utils/trace.h>
+ #endif
+
#ifndef HAVE_MEMMOVE
#include <regex/utils.h>
#else
***************
*** 93,98 ****
--- 98,106 ----
int i;
int numberOfAttributes = tupleDesc->natts;
Form_pg_attribute *att = tupleDesc->attrs;
+ #ifdef FREE_TUPLE_MEMORY
+ bool free_tuple_memory = pg_options[OPT_FREE_TUPLE_MEMORY];
+ #endif

if (bit != NULL)
{
***************
*** 131,136 ****
--- 139,152 ----
*infomask |= HEAP_HASVARLENA;
data_length = VARSIZE(DatumGetPointer(value[i]));
memmove(data, DatumGetPointer(value[i]), data_length);
+ #ifdef FREE_TUPLE_MEMORY
+ /* try to pfree value[i] - dz */
+ if (free_tuple_memory &&
+ PortalHeapMemoryIsValid(CurrentMemoryContext,
+ (Pointer) value[i])) {
+ pfree(value[i]);
+ }
+ #endif
break;
case sizeof(char):
*data = att[i]->attbyval ?
***************
*** 147,154 ****
*((int32 *) value[i]));
break;
default:
! memmove(data, DatumGetPointer(value[i]),
! att[i]->attlen);
break;
}
data = (char *) att_addlength((long) data, att[i]->attlen, value[i]);
--- 163,177 ----
*((int32 *) value[i]));
break;
default:
! memmove(data, DatumGetPointer(value[i]), att[i]->attlen);
! #ifdef FREE_TUPLE_MEMORY
! /* try to pfree value[i] - dz */
! if (free_tuple_memory &&
! PortalHeapMemoryIsValid(CurrentMemoryContext,
! (Pointer) value[i])) {
! pfree(value[i]);
! }
! #endif
break;
}
data = (char *) att_addlength((long) data, att[i]->attlen, value[i]);
*** src/backend/executor/nodeAgg.c.orig Wed May 26 09:02:57 1999
--- src/backend/executor/nodeAgg.c Fri Jun 11 19:10:27 1999
***************
*** 31,36 ****
--- 31,41 ----
#include "utils/syscache.h"
#include "optimizer/clauses.h"

+ #ifdef FREE_TUPLE_MEMORY
+ #include <utils/portal.h>
+ #include <utils/trace.h>
+ #endif
+
/*
* AggFuncInfo -
* keeps the transition functions information around
***************
*** 113,119 ****
isNull1 = FALSE,
isNull2 = FALSE;
bool qual_result;
!

/* ---------------------
* get state info from node
--- 118,126 ----
isNull1 = FALSE,
isNull2 = FALSE;
bool qual_result;
! #ifdef FREE_TUPLE_MEMORY
! bool free_tuple_memory = pg_options[OPT_FREE_TUPLE_MEMORY];
! #endif

/* ---------------------
* get state info from node
***************
*** 241,246 ****
--- 248,257 ----
for (;;)
{
TupleTableSlot *outerslot;
+ #ifdef FREE_TUPLE_MEMORY
+ Oid valueType;
+ bool isByValue = 0;
+ #endif

isNull = isNull1 = isNull2 = 0;
outerslot = ExecProcNode(outerPlan, (Plan *) node);
***************
*** 293,298 ****
--- 304,334 ----
newVal = ExecEvalExpr(aggref->target, econtext,
&isNull, &isDone);
}
+ #ifdef FREE_TUPLE_MEMORY
+ if (free_tuple_memory) {
+ switch (nodeTag(aggref->target)) {
+ case T_Const:
+ isByValue = ((Const*) (aggref->target))->constbyval;
+ break;
+ case T_Var:
+ valueType = ((Var*) (aggref->target))->vartype;
+ isByValue = typeByVal(typeidType(valueType));
+ break;
+ case T_Array:
+ isByValue = ((Array*)(aggref->target))->arrayelembyval;
+ break;
+ case T_ArrayRef:
+ isByValue =((ArrayRef*)(aggref->target))->refelembyval;
+ break;
+ case T_Expr:
+ valueType = ((Expr*) (aggref->target))->typeOid;
+ isByValue = typeByVal(typeidType(valueType));
+ break;
+ default:
+ break;
+ }
+ }
+ #endif

if (isNull && !aggref->usenulls)
continue; /* ignore this tuple for this agg */
***************
*** 353,358 ****
--- 389,404 ----
(FmgrValues *) args, &isNull2);
Assert(!isNull2);
}
+
+ #ifdef FREE_TUPLE_MEMORY
+ /* try to pfree newVal if not isByValue - dz */
+ if (free_tuple_memory && !isByValue &&
+ PortalHeapMemoryIsValid(CurrentMemoryContext,
+ (Pointer) newVal))
+ {
+ pfree(newVal);
+ }
+ #endif
}

/*

--
Massimo Dal Zotto

+----------------------------------------------------------------------+
| Massimo Dal Zotto email: dz(at)cs(dot)unitn(dot)it |
| Via Marconi, 141 phone: ++39-0461534251 |
| 38057 Pergine Valsugana (TN) www: http://www.cs.unitn.it/~dz/ |
| Italy pgp: finger dz(at)tango(dot)cs(dot)unitn(dot)it |
+----------------------------------------------------------------------+