[PATCH] vinyl: fix vy_range_update_compaction_priority hang

[Vladimir Davydov]

Under certain circumstances vy_slice_new() may create an empty slice,
e.g. on range split:

   |------------------ Slice ---------------|
                         |---- Run -----|
                     +
                  split key
   |---- Slice 1 ----||------ Slice 2 ------|
         ^^^^^^^
          Empty

vy_range_update_compaction_priority() uses the size of the last slice in
a range as a base for LSM tree level sizing. If the slice size happens
to be 0, it will simply hang in an infinite loop. Fix this potential
hang by using 1 if the last slice size is 0.
---
https://github.com/tarantool/tarantool/commits/dv/vy-fix-compaction-prio-calc-hang

 src/box/vy_range.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/src/box/vy_range.c b/src/box/vy_range.c
index 395639dc..4ff85211 100644
--- a/src/box/vy_range.c
+++ b/src/box/vy_range.c
@@ -343,7 +343,7 @@ vy_range_update_compaction_priority(struct vy_range *range,
 	uint64_t size;
 	struct vy_slice *slice;
 	slice = rlist_last_entry(&range->slices, struct vy_slice, in_range);
-	size = slice->count.bytes;
+	size = MAX(slice->count.bytes, 1);
 	slice = rlist_first_entry(&range->slices, struct vy_slice, in_range);
 	do {
 		target_run_size = size;
-- 
2.11.0