Datum
adaptive_merge_agg(PG_FUNCTION_ARGS)
{
AdaptiveCounter counter1;
AdaptiveCounter counter2 = (AdaptiveCounter)PG_GETARG_BYTEA_P(1);
/* is the counter created (if not, create it - error 1%, 10mil items) */
if (PG_ARGISNULL(0)) {
/* just copy the second estimator into the first one */
counter1 = ac_copy(counter2);
} else {
/* ok, we already have the estimator - merge the second one into it */
counter1 = (AdaptiveCounter)PG_GETARG_BYTEA_P(0);
/* perform the merge (in place) */
counter1 = ac_merge(counter1, counter2, true);
}
/* return the updated bytea */
PG_RETURN_BYTEA_P(counter1);
}
/* Merge an adaptive counter into another one. The first parameter 'dest' is the target
* counter that will be modified during the merge.
*
* The counters have to be 'the same' i.e. the basic parameters (level, length, itemSize
* and error rate) need to be equal.
*/
AdaptiveCounter ac_merge(AdaptiveCounter dest, AdaptiveCounter src) {
AdaptiveCounter result;
int i = 0;
/* check if we need to swap dest/src - we need the destination to have
* higher (>=) level and lower item size (<=) at the same time */
if ((dest->level < src->level) ||
((dest->level == src->level) && (dest->itemSize > src->itemSize))) {
return ac_merge(src, dest);
}
/* it's possible to have (dest->level > src->level) and
* (dest->itemSize > src->itemSize) at the same time, which makes
* the counters impossible to merge. */
/* check that the counters are 'mergeable' - there are two
* conditions:
*
* 1) Lower level has to be merged into the higher level (this is
* assured thanks to the previous swap, so we have assert here).
*
* 2) The destination item size must not be higher than the source.
*
* Anyway the best way to make sure two counters are mergeable is
* to use exactly the same counters (error rate, item length).
*
* Maybe there should be another condition on maxItems, but I don't
* think so.
*/
assert(dest->level >= src->level);
if (dest->itemSize > src->itemSize) {
elog(ERROR, "counters not mergeable - item length dest=%d > src=%d ",
dest->itemSize, src->itemSize);
}
/* allocate space for the destination counter (mergeable -> same size) */
result = ac_create_copy(dest);
/* copy the items (from the src counter, the one with the lower level) */
for (i = 0; i < src->items; i++) {
ac_add_hash(result, &(src->bitmap[i*src->itemSize]));
}
return result;
}
Datum
adaptive_merge_simple(PG_FUNCTION_ARGS)
{
AdaptiveCounter counter1 = (AdaptiveCounter)PG_GETARG_BYTEA_P(0);
AdaptiveCounter counter2 = (AdaptiveCounter)PG_GETARG_BYTEA_P(1);
/* is the counter created (if not, create it - error 1%, 10mil items) */
if (PG_ARGISNULL(0) && PG_ARGISNULL(1)) {
PG_RETURN_NULL();
} else if (PG_ARGISNULL(0)) {
PG_RETURN_BYTEA_P(ac_copy(counter2));
} else if (PG_ARGISNULL(1)) {
PG_RETURN_BYTEA_P(ac_copy(counter1));
} else {
PG_RETURN_BYTEA_P(ac_merge(counter1, counter2, false));
}
}
