Merge pull request #929 from wiredtiger/extlist-merge-swap

Make extent list management more efficient during checkpoints

2 files changed, 24 insertions, 2 deletions

diff --git a/src/block/block_ckpt.c b/src/block/block_ckpt.c
index 690c6dffd34..38921a026cf 100644
--- a/src/block/block_ckpt.c
+++ b/src/block/block_ckpt.c
@@ -30,7 +30,7 @@ __wt_block_ckpt_init(
 	WT_RET(__wt_block_extlist_init(
 	    session, &ci->discard, name, "discard", 0));
 	WT_RET(__wt_block_extlist_init(
-	    session, &ci->ckpt_avail, name, "ckpt_avail", 0));
+	    session, &ci->ckpt_avail, name, "ckpt_avail", 1));
 
 	return (0);
 }
@@ -366,7 +366,7 @@ __ckpt_process(
 	 */
 	__wt_block_extlist_free(session, &ci->ckpt_avail);
 	WT_RET(__wt_block_extlist_init(
-	    session, &ci->ckpt_avail, "live", "ckpt_avail", 0));
+	    session, &ci->ckpt_avail, "live", "ckpt_avail", 1));
 
 	/*
 	 * We've allocated our last page, update the checkpoint size.  We need
diff --git a/src/block/block_ext.c b/src/block/block_ext.c
index 9b31cbf31a3..583b0b59961 100644
--- a/src/block/block_ext.c
+++ b/src/block/block_ext.c
@@ -880,9 +880,31 @@ int
 __wt_block_extlist_merge(WT_SESSION_IMPL *session, WT_EXTLIST *a, WT_EXTLIST *b)
 {
 	WT_EXT *ext;
+	WT_EXTLIST tmp;
+	u_int i;
 
 	WT_VERBOSE_RET(session, block, "merging %s into %s", a->name, b->name);
 
+	/*
+	 * Sometimes the list we are merging is much bigger than the other: if
+	 * so, swap the lists around to reduce the amount of work we need to do
+	 * during the merge.  The size lists have to match as well, so this is
+	 * only possible if both lists are tracking sizes, or neither are.
+	 */
+	if (a->track_size == b->track_size && a->entries > b->entries) {
+		tmp = *a;
+		a->bytes = b->bytes;
+		b->bytes = tmp.bytes;
+		a->entries = b->entries;
+		b->entries = tmp.entries;
+		for (i = 0; i < WT_SKIP_MAXDEPTH; i++) {
+			a->off[i] = b->off[i];
+			b->off[i] = tmp.off[i];
+			a->sz[i] = b->sz[i];
+			b->sz[i] = tmp.sz[i];
+		}
+	}
+
 	WT_EXT_FOREACH(ext, a->off)
 		WT_RET(__block_merge(session, b, ext->off, ext->size));