Changeset: 265dfc40540c for MonetDB
URL: https://dev.monetdb.org/hg/MonetDB/rev/265dfc40540c
Modified Files:
gdk/gdk_sample.c
Branch: default
Log Message:
Generate a list of random numbers before checking for duplicates.
This means we quickly generate the numbers with a single locking
operation instead of locking and unlocking all the time.
diffs (64 lines):
diff --git a/gdk/gdk_sample.c b/gdk/gdk_sample.c
--- a/gdk/gdk_sample.c
+++ b/gdk/gdk_sample.c
@@ -129,28 +129,40 @@ do_batsample(BAT *b, BUN n, random_state
return NULL;
}
- /* while we do not have enough sample OIDs yet */
+ /* generate a list of random numbers; note we use the
+ * "tree" array, but we use the value from each location
+ * before it is overwritten by the use as part of the
+ * binary tree */
if (lock) {
- /* serialize access to random state engine */
- for (rescnt = 0; rescnt < n; rescnt++) {
- oid candoid;
- do {
- MT_lock_set(lock);
- candoid = minoid + next(rse) % cnt;
- MT_lock_unset(lock);
- /* if that candidate OID was already
- * generated, try again */
- } while (!OIDTreeMaybeInsert(tree, candoid,
rescnt));
- }
+ MT_lock_set(lock);
+ for (rescnt = 0; rescnt < n; rescnt++)
+ tree[rescnt].o = next(rse);
+ MT_lock_unset(lock);
} else {
- for (rescnt = 0; rescnt < n; rescnt++) {
- oid candoid;
- do {
- candoid = minoid + next(rse) % cnt;
- /* if that candidate OID was already
- * generated, try again */
- } while (!OIDTreeMaybeInsert(tree, candoid,
rescnt));
- }
+ for (rescnt = 0; rescnt < n; rescnt++)
+ tree[rescnt].o = next(rse);
+ }
+
+ /* while we do not have enough sample OIDs yet */
+ BUN rnd = 0;
+ for (rescnt = 0; rescnt < n; rescnt++) {
+ oid candoid;
+ do {
+ if (rnd == n) {
+ /* we ran out of random numbers,
+ * so generate more */
+ if (lock)
+ MT_lock_set(lock);
+ for (rnd = rescnt; rnd < n; rnd++)
+ tree[rnd].o = next(rse);
+ if (lock)
+ MT_lock_unset(lock);
+ rnd = rescnt;
+ }
+ candoid = minoid + tree[rnd++].o % cnt;
+ /* if that candidate OID was already
+ * generated, try again */
+ } while (!OIDTreeMaybeInsert(tree, candoid, rescnt));
}
if (!antiset) {
OIDTreeToBAT(tree, bn);
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