MonetDB: Jan2022 - increase critical section of rw lock:

[Aris Koning]

Changeset: dcc6f9951a32 for MonetDB
URL: https://dev.monetdb.org/hg/MonetDB/rev/dcc6f9951a32
Modified Files:
        sql/storage/objectset.c
Branch: Jan2022
Log Message:

increase critical section of rw lock:
Concurrently unlocking the read lock in the rw lock is a costly operation
and when concurrently executed in a big loop becomes a major bottleneck.
Increasing the critical section to cover the entire loop, improves the
performance quite a bit.


diffs (39 lines):

diff --git a/sql/storage/objectset.c b/sql/storage/objectset.c
--- a/sql/storage/objectset.c
+++ b/sql/storage/objectset.c
@@ -1095,6 +1095,7 @@ oi_next(struct os_iter *oi)
        if (oi->name) {
                versionhead  *n = oi->n;
 
+               lock_reader(oi->os); /* intentionally outside of while loop */
                while (n && !b) {
 
                        if (n->ov->b->name && strcmp(n->ov->b->name, oi->name) 
== 0) {
@@ -1105,24 +1106,23 @@ oi_next(struct os_iter *oi)
                                if (ov && os_atmc_get_state(ov) == active)
                                        b = ov->b;
                        } else {
-                               lock_reader(oi->os);
                                n = oi->n = n->next;
-                               unlock_reader(oi->os);
                        }
                }
+               unlock_reader(oi->os);
        } else {
                versionhead  *n = oi->n;
 
+               lock_reader(oi->os); /* intentionally outside of while loop */
                while (n && !b) {
                        objectversion *ov = n->ov;
-                       lock_reader(oi->os);
                        n = oi->n = n->next;
-                       unlock_reader(oi->os);
 
                        ov = get_valid_object_id(oi->tr, ov);
                        if (ov && os_atmc_get_state(ov) == active)
                                b = ov->b;
                }
+               unlock_reader(oi->os);
        }
        return b;
 }
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