[PATCH 4/7] vinyl: fix force compaction logic

[Vladimir Davydov <vdavydov.dev@gmail.com>]

This patch address a few problems index.compact() is suffering from,
namely:

 - When a range is split or coalesced, it should inherit the value of
   needs_compaction flag from the source ranges. Currently, the flag is
   cleared so that the resulting range may be not compacted.

 - If a range has no slices, we shouldn't set needs_compaction flag for
   it, because obviously it can't be compacted, but we do.

 - The needs_compaction flag should be cleared as soon as we schedule a
   range for compaction, not when all slices have been compacted into
   one, as we presently expect, because the latter may never happen
   under a write-intensive load.
---
 src/box/vy_lsm.c       |  9 +++++++--
 src/box/vy_range.c     | 16 ++--------------
 src/box/vy_range.h     |  8 ++------
 src/box/vy_scheduler.c |  2 ++
 4 files changed, 13 insertions(+), 22 deletions(-)

diff --git a/src/box/vy_lsm.c b/src/box/vy_lsm.c
index 15592fbf..a0d211f8 100644
--- a/src/box/vy_lsm.c
+++ b/src/box/vy_lsm.c
@@ -1040,6 +1040,7 @@ vy_lsm_split_range(struct vy_lsm *lsm, struct vy_range *range)
 			if (new_slice != NULL)
 				vy_range_add_slice(part, new_slice);
 		}
+		part->needs_compaction = range->needs_compaction;
 		part->compact_priority = range->compact_priority;
 	}
 
@@ -1147,6 +1148,8 @@ vy_lsm_coalesce_range(struct vy_lsm *lsm, struct vy_range *range)
 		rlist_splice(&result->slices, &it->slices);
 		result->slice_count += it->slice_count;
 		vy_disk_stmt_counter_add(&result->count, &it->count);
+		if (it->needs_compaction)
+			result->needs_compaction = true;
 		vy_range_delete(it);
 		it = next;
 	}
@@ -1181,8 +1184,10 @@ vy_lsm_force_compaction(struct vy_lsm *lsm)
 	struct vy_range_tree_iterator it;
 
 	vy_range_tree_ifirst(lsm->tree, &it);
-	while ((range = vy_range_tree_inext(&it)) != NULL)
-		vy_range_force_compaction(range);
+	while ((range = vy_range_tree_inext(&it)) != NULL) {
+		range->needs_compaction = true;
+		vy_range_update_compact_priority(range, &lsm->opts);
+	}
 
 	vy_range_heap_update_all(&lsm->range_heap);
 }
diff --git a/src/box/vy_range.c b/src/box/vy_range.c
index 6a55a018..ddcd2ed3 100644
--- a/src/box/vy_range.c
+++ b/src/box/vy_range.c
@@ -262,18 +262,6 @@ vy_range_remove_slice(struct vy_range *range, struct vy_slice *slice)
 	vy_disk_stmt_counter_sub(&range->count, &slice->count);
 }
 
-void
-vy_range_force_compaction(struct vy_range *range)
-{
-	if (range->slice_count == 1) {
-		/* Already compacted. */
-		assert(!range->needs_compaction);
-		return;
-	}
-	range->needs_compaction = true;
-	range->compact_priority = range->slice_count;
-}
-
 /**
  * To reduce write amplification caused by compaction, we follow
  * the LSM tree design. Runs in each range are divided into groups
@@ -304,9 +292,9 @@ vy_range_update_compact_priority(struct vy_range *range,
 	assert(opts->run_count_per_level > 0);
 	assert(opts->run_size_ratio > 1);
 
-	if (range->slice_count == 1) {
+	if (range->slice_count <= 1) {
 		/* Nothing to compact. */
-		range->compact_priority = 1;
+		range->compact_priority = 0;
 		range->needs_compaction = false;
 		return;
 	}
diff --git a/src/box/vy_range.h b/src/box/vy_range.h
index d7031e70..2ca19a1c 100644
--- a/src/box/vy_range.h
+++ b/src/box/vy_range.h
@@ -110,8 +110,8 @@ struct vy_range {
 	 * If this flag is set, the range must be scheduled for
 	 * major compaction, i.e. its compact_priority must be
 	 * raised to max (slice_count). The flag is set by
-	 * vy_range_force_compaction() and cleared automatically
-	 * when all slices of the range have been compacted.
+	 * vy_lsm_force_compaction() and cleared when the range
+	 * is scheduled for compaction.
 	 */
 	bool needs_compaction;
 	/** Number of times the range was compacted. */
@@ -229,10 +229,6 @@ vy_range_add_slice_before(struct vy_range *range, struct vy_slice *slice,
 void
 vy_range_remove_slice(struct vy_range *range, struct vy_slice *slice);
 
-/** Mark a range for major compaction. */
-void
-vy_range_force_compaction(struct vy_range *range);
-
 /**
  * Update compaction priority of a range.
  *
diff --git a/src/box/vy_scheduler.c b/src/box/vy_scheduler.c
index 4959300e..a1ae3f54 100644
--- a/src/box/vy_scheduler.c
+++ b/src/box/vy_scheduler.c
@@ -1604,6 +1604,8 @@ vy_task_compact_new(struct vy_scheduler *scheduler, struct vy_lsm *lsm,
 	assert(n == 0);
 	assert(new_run->dump_lsn >= 0);
 
+	range->needs_compaction = false;
+
 	task->range = range;
 	task->new_run = new_run;
 	task->wi = wi;
-- 
2.11.0