[Tarantool-patches] [PATCH v2 2/2] memtx: increase the memory quota if needed to truncate or delete

[Ilya Kosarev <i.kosarev@tarantool.org>]

Trying to perform space:truncate() and space:delete() while reaching
memtx_memory limit we could experience slab allocator failure. This
behavior seems to be quite surprising for users. Now we are increasing
memtx quota if needed for truncation or deletion. After performing it
quota is being set back to the previous value if possible, while it
should be so for almost any case, since we are meant to free some space
during deletion or truncation.

Closes #3807
---
 src/box/box.cc         | 34 +++++++++++++++++++++++++++++++++-
 src/box/memtx_engine.c | 18 ++++++++++++++++++
 src/box/memtx_engine.h |  5 +++++
 3 files changed, 56 insertions(+), 1 deletion(-)

diff --git a/src/box/box.cc b/src/box/box.cc
index 1b2b27d61..03e2f3cc9 100644
--- a/src/box/box.cc
+++ b/src/box/box.cc
@@ -1250,7 +1250,26 @@ box_delete(uint32_t space_id, uint32_t index_id, const char *key,
 	request.index_id = index_id;
 	request.key = key;
 	request.key_end = key_end;
-	return box_process1(&request, result);
+
+	struct space *space = space_cache_find(space_id);
+	if (space == NULL)
+		return -1;
+	struct memtx_engine *memtx =
+		(struct memtx_engine *)space->engine;
+	size_t total;
+	bool extended;
+	memtx_engine_guarantee_memory(memtx, memtx->arena.slab_size,
+				      &total, &extended);
+
+	int rc = box_process1(&request, result);
+
+	if (extended) {
+		size_t new_total = quota_set(&memtx->quota, total);
+		if (new_total > total)
+			quota_set(&memtx->quota, quota_used(&memtx->quota));
+	}
+
+	return rc;
 }
 
 int
@@ -1321,9 +1340,22 @@ space_truncate(struct space *space)
 	ops_buf_end = mp_encode_uint(ops_buf_end, 1);
 	assert(ops_buf_end < buf + buf_size);
 
+	struct memtx_engine *memtx =
+		(struct memtx_engine *)space->engine;
+	size_t total;
+	bool extended;
+	memtx_engine_guarantee_memory(memtx, memtx->arena.slab_size,
+				      &total, &extended);
+
 	if (box_upsert(BOX_TRUNCATE_ID, 0, tuple_buf, tuple_buf_end,
 		       ops_buf, ops_buf_end, 0, NULL) != 0)
 		diag_raise();
+
+	if (extended) {
+		size_t new_total = quota_set(&memtx->quota, total);
+		if (new_total > total)
+			quota_set(&memtx->quota, quota_used(&memtx->quota));
+	}
 }
 
 int
diff --git a/src/box/memtx_engine.c b/src/box/memtx_engine.c
index 23ccc4703..cbac015e3 100644
--- a/src/box/memtx_engine.c
+++ b/src/box/memtx_engine.c
@@ -1090,6 +1090,24 @@ memtx_engine_set_memory(struct memtx_engine *memtx, size_t size)
 	return 0;
 }
 
+void
+memtx_engine_guarantee_memory(struct memtx_engine *memtx,
+			      size_t request, size_t *old_total,
+			      bool *extended)
+{
+	struct quota *memtx_quota = &memtx->quota;
+	size_t total, used;
+	quota_get_total_and_used(memtx_quota, &total, &used);
+	*old_total = total;
+	if (total - used < request) {
+		quota_set(memtx_quota,
+			  total + request - (total - used));
+		*extended = true;
+		return;
+	}
+	*extended = false;
+}
+
 void
 memtx_engine_set_max_tuple_size(struct memtx_engine *memtx, size_t max_size)
 {
diff --git a/src/box/memtx_engine.h b/src/box/memtx_engine.h
index f562c66df..f74f65e96 100644
--- a/src/box/memtx_engine.h
+++ b/src/box/memtx_engine.h
@@ -213,6 +213,11 @@ memtx_engine_set_snap_io_rate_limit(struct memtx_engine *memtx, double limit);
 int
 memtx_engine_set_memory(struct memtx_engine *memtx, size_t size);
 
+void
+memtx_engine_guarantee_memory(struct memtx_engine *memtx,
+			      size_t request, size_t *old_total,
+			      bool *extended);
+
 void
 memtx_engine_set_max_tuple_size(struct memtx_engine *memtx, size_t max_size);
 
-- 
2.17.1