I have a couple functions which form the basis of an aggregate. The purpose of
the aggregate function is to be able to perform a GROUP BY on a one to many
table and produce a summary able where all the "many" integers will be packed
in a single array. If this were a text search query, rather than searching
hundreds of entries in the table, one fetch and possibly a detoast is used. It
is MUCH faster for my purpose.
It is used like this:
create table array_lookup as select id1, int_array_aggregate(id2) from lookup
group by (id1) ;
I have written a good number of functions in PGSQL, I'm not a newbe. Could
someone take a look at it? I don't think I am doing anything that would kill
the back end, so it may be a bug in RC3, I am just pulling my hair out. (FYI,
the one to many table may have thousands of rows for an entry.) One more thing:
I'm not getting any elog messages, so it should not be a memory issue.
>>>>>>>>>>>>>>>>
-- Internal function for the aggregate
-- Is called for each item in an aggregation
create function int_agg_state (int4, int4) returns int4 as 'MODULE_FILENAME','int_agg_state' language
'c';
-- Internal function for the aggregate
-- Is called at the end of the aggregation, and returns an array.
create function int_agg_final_array (int4) returns int4[] as 'MODULE_FILENAME','int_agg_final_array'
language'c';
-- The aggration funcion.
-- uses the above functions to create an array of integers from an aggregation.
create aggregate int_array_aggregate
( BASETYPE = int4, SFUNC = int_agg_state, STYPE = int4, FINALFUNC = int_agg_final_array,
INITCOND= 0
);
>>>>>>>>>>>>>>>>
/* This is actually a postgres version of a one dimentional array */
typedef struct agg
{ ArrayType a; int items; /* Number of items in array */ int lower; /* Lower bounds of array,
usedas max during aggregation
*/ int4 array[1];
}PGARRAY;
#define TOASTED 1
#define START_NUM 8
#define PGARRAY_SIZE(n) (sizeof(PGARRAY) + ((n-1)*sizeof(int4)))
PGARRAY * GetPGArray(int4 state, int fAdd);
Datum int_agg_state(PG_FUNCTION_ARGS);
Datum int_agg_final_array(PG_FUNCTION_ARGS);
PG_FUNCTION_INFO_V1(int_agg_state);
PG_FUNCTION_INFO_V1(int_agg_final_array);
/* Manage the aggregation state of the array */
PGARRAY * GetPGArray(int4 state, int fAdd)
{ PGARRAY *p = (PGARRAY *) state; if(!state) { /* New array */ int cb =
PGARRAY_SIZE(START_NUM);
p = (PGARRAY *) palloc(cb);
if(!p) { elog(ERROR,"Integer aggregator, cant allocate
memory\n"); return 0; }
p->a.size = cb; p->a.ndim= 0; p->a.flags = 0; p->items = 0;
p->lower= START_NUM; return p; } else if(fAdd) { /* Ensure
arrayhas space */ if(p->items >= p->lower) { PGARRAY *pn;
int n = p->lower + p->lower; int cbNew = PGARRAY_SIZE(n); pn =
(PGARRAY*) palloc(cbNew);
if(!pn) { elog(ERROR,"Integer aggregator,
cantallocate
memory\n"); } else {
memcpy(pn,p, p->a.size); pn->a.size = cbNew; pn->lower = n;
pfree(p); return pn; } }
} return p;
}
/* Called for each iteration during an aggregate function */
Datum int_agg_state(PG_FUNCTION_ARGS)
{ int4 state = PG_GETARG_INT32(0); int4 value = PG_GETARG_INT32(1);
PGARRAY *p = GetPGArray(state, 1); if(!p) { elog(ERROR,"No aggregate storage\n");
} else if(p->items >= p->lower) { elog(ERROR,"aggregate storage too small\n"); }
else { p->array[p->items++]= value; } PG_RETURN_INT32(p);
}
/* This is the final function used for the integer aggregator. It returns all
the integers* collected as a one dimentional integer array */
Datum int_agg_final_array(PG_FUNCTION_ARGS)
{ PGARRAY *p = GetPGArray(PG_GETARG_INT32(0),0);
if(p) { /* Fix up the fields in the structure, so Postgres understands
*/ p->a.size = PGARRAY_SIZE(p->items); p->a.ndim=1; p->a.flags = 0;
p->lower = 0; PG_RETURN_POINTER(p); } PG_RETURN_NULL();
}