MonetDB: default - Implemented another trivial case for grouping...

[Stefan Manegold]

;-)

Dank je wel! --- Niet alleen voor deze, maar met naam ook voor de hele
nieuwe group-by code en al die andere nieuwe schone code!!!

Stefan

Changeset: 6f001c03cd8d for MonetDB
URL: http://dev.monetdb.org/hg/MonetDB?cmd=changeset;node=6f001c03cd8d
gdk/gdk_group.c
Branch: default
Implemented another trivial case for grouping: all equal values.
diff --git a/gdk/gdk_group.c b/gdk/gdk_group.c
--- a/gdk/gdk_group.c
+++ b/gdk/gdk_group.c
@@ -44,11 +44,14 @@
* is always created. In other words, the groups argument may not be
* NULL, but the extents and histo arguments may be NULL.
*
- * There are five different implementations of the grouping code.
+ * There are six different implementations of the grouping code.
*
* If it can be trivially determined that all groups are singletons,
* we can produce the outputs trivially.
*
+ * If all values in b are known to be equal (both sorted and reverse
+ * sorted), we produce a single group or copy the input group.
+ *
* If the input bats b and g are sorted, or if the subsorted flag is
* set (only used by BATsubsort), we only need to compare consecutive
* values.
@@ -102,6 +105,7 @@ BATgroup_internal(BAT **groups, BAT **ex
if (b->tkey || BATcount(b) <= 1 || (g && (g->tkey || BATtdense(g)))) {
/* grouping is trivial: 1 element per group */
+ ALGODEBUG fprintf(stderr, "#BATgroup: trivial case: 1 element per group\n");
if (BATcount(b) == 1 && b->htype == TYPE_oid)
ngrp = * (oid *) Hloc(b, BUNfirst(b));
else
@@ -132,6 +136,62 @@ BATgroup_internal(BAT **groups, BAT **ex
}
return GDK_SUCCEED;
}
+ if (b->tsorted && b->trevsorted) {
+ /* all values are equal */
+ if (g == NULL) {
+ /* there's only a single group: 0 */
+ ALGODEBUG fprintf(stderr, "#BATgroup: trivial case: single output group\n");
+ ngrp = 0;
+ gn = BATconstant(TYPE_oid, &ngrp, BATcount(b));
+ if (gn == NULL)
+ goto error;
+ BATseqbase(gn, b->hseqbase);
+ *groups = gn;
+ if (extents) {
+ ngrp = gn->hseqbase;
+ en = BATconstant(TYPE_void, &ngrp, 1);
+ if (en == NULL)
+ goto error;
+ BATseqbase(BATmirror(en), ngrp);
+ *extents = en;
+ }
+ if (histo) {
+ wrd cnt = (wrd) BATcount(b);
+
+ hn = BATconstant(TYPE_wrd, &cnt, 1);
+ if (hn == NULL)
+ goto error;
+ *histo = hn;
+ }
+ return GDK_SUCCEED;
+ }
+ if ((extents == NULL) == (e == NULL) &&
+ (histo == NULL) == (h == NULL)) {
+ /* inherit given grouping; note that if
+ * extents/histo is to be returned, we need
+ * e/h available in order to copy them,
+ * otherwise we will need to calculate them
+ * which we will do using the "normal" case */
+ ALGODEBUG fprintf(stderr, "#BATgroup: trivial case: copy input groups\n");
+ gn = BATcopy(g, g->htype, g->ttype, 0);
+ if (gn == NULL)
+ goto error;
+ *groups = gn;
+ if (extents) {
+ en = BATcopy(e, e->htype, e->ttype, 0);
+ if (en == NULL)
+ goto error;
+ *extents = en;
+ }
+ if (histo) {
+ hn = BATcopy(h, h->htype, h->ttype, 0);
+ if (hn == NULL)
+ goto error;
+ *histo = hn;
+ }
+ return GDK_SUCCEED;
+ }
+ }
assert(g == NULL || !BATtdense(g)); /* i.e. g->ttype == TYPE_oid */
bi = bat_iterator(b);
cmp = BATatoms[b->ttype].atomCmp;
@@ -167,6 +227,7 @@ BATgroup_internal(BAT **groups, BAT **ex
(g == NULL || g->tsorted || g->trevsorted)) ||
subsorted) {
/* we only need to compare each entry with the previous */
+ ALGODEBUG fprintf(stderr, "#BATgroup: compare consecutive values\n");
if (grps)
prev = *grps++;
pv = BUNtail(bi, BUNfirst(b));
@@ -220,6 +281,7 @@ BATgroup_internal(BAT **groups, BAT **ex
/* for each value, we need to scan all previous equal
* values (a consecutive, possibly empty, range) to
* see if we can find one in the same old group */
+ ALGODEBUG fprintf(stderr, "#BATgroup: subscan old groups\n");
pv = BUNtail(bi, BUNfirst(b));
ngrps[0] = ngrp;
if (extents)
@@ -284,6 +346,7 @@ BATgroup_internal(BAT **groups, BAT **ex
}
} else if (b->T->hash) {
/* we already have a hash table on b */
+ ALGODEBUG fprintf(stderr, "#BATgroup: use existing hash table\n");
hs = b->T->hash;
for (r = BUNfirst(b), p = r, q = r + BATcount(b); p < q; p++) {
v = BUNtail(bi, p);
@@ -343,6 +406,7 @@ BATgroup_internal(BAT **groups, BAT **ex
* build an incomplete hash table on the fly--also see
* BATassertHeadProps and BATderiveHeadProps for
* similar code */
+ ALGODEBUG fprintf(stderr, "#BATgroup: create partial hash table\n");
nme = BBP_physical(b->batCacheid);
nmelen = strlen(nme);
if ((hp = GDKzalloc(sizeof(Heap))) == NULL ||
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