[PATCH v2 2/4] schema: add space names cache

[Kirill Yukhin]

Since SQL is heavily using name -> space mapping,
introduce (instead of scanning _space space) dedicated
cache, which maps space name to space pointer.
---
 src/box/schema.cc | 58 ++++++++++++++++++++++++++++++++++++++++++++++++++++++-
 src/box/schema.h  |  8 ++++++++
 2 files changed, 65 insertions(+), 1 deletion(-)

diff --git a/src/box/schema.cc b/src/box/schema.cc
index 08457a46..b931fdf 100644
--- a/src/box/schema.cc
+++ b/src/box/schema.cc
@@ -55,6 +55,7 @@
 
 /** All existing spaces. */
 static struct mh_i32ptr_t *spaces;
+static struct mh_strnptr_t *spaces_by_name;
 static struct mh_i32ptr_t *funcs;
 static struct mh_strnptr_t *funcs_by_name;
 static struct mh_i32ptr_t *sequences;
@@ -95,6 +96,17 @@ space_by_id(uint32_t id)
 	return (struct space *) mh_i32ptr_node(spaces, space)->val;
 }
 
+/** Return space by its name */
+struct space *
+space_by_name(const char *name)
+{
+	mh_int_t space = mh_strnptr_find_inp(spaces_by_name, name,
+					     strlen(name));
+	if (space == mh_end(spaces_by_name))
+		return NULL;
+	return (struct space *) mh_strnptr_node(spaces_by_name, space)->val;
+}
+
 /** Return current schema version */
 uint32_t
 box_schema_version()
@@ -165,7 +177,25 @@ void
 space_cache_replace(struct space *old_space, struct space *new_space)
 {
 	assert(new_space != NULL || old_space != NULL);
+	struct space *old_space_by_n = NULL;
 	if (new_space != NULL) {
+		/*
+		 * If replacing is performed and space name was
+		 * changed, then need to explicitly remove old
+		 * entry from spaces cache.
+		 * NB: Since space_id never changed - no need
+		 * to do so for space_id cache.
+		 */
+		if (old_space != NULL && strcmp(space_name(old_space),
+						new_space->def->name) != 0) {
+			const char *name = space_name(old_space);
+			mh_int_t k = mh_strnptr_find_inp(spaces_by_name, name,
+							 strlen(name));
+			assert(k != mh_end(spaces_by_name));
+			mh_strnptr_del(spaces_by_name, k, NULL);
+			old_space_by_n = (struct space *)mh_strnptr_node(spaces_by_name,
+									 k)->val;
+		}
 		const struct mh_i32ptr_node_t node_p = { space_id(new_space),
 							 new_space };
 		struct mh_i32ptr_node_t old, *p_old = &old;
@@ -174,7 +204,23 @@ space_cache_replace(struct space *old_space, struct space *new_space)
 			panic_syserror("Out of memory for the data "
 				       "dictionary cache.");
 		}
-		assert((struct space *)p_old->val == old_space);
+		const char *name = space_name(new_space);
+		uint32_t name_len = strlen(name);
+		uint32_t hash = mh_strn_hash(name, name_len);
+		const struct mh_strnptr_node_t node_s = { name, name_len, hash,
+							  new_space };
+		struct mh_strnptr_node_t old_s, *p_old_s = &old_s;
+		k = mh_strnptr_put(spaces_by_name, &node_s, &p_old_s, NULL);
+		if (k == mh_end(spaces_by_name)) {
+			panic_syserror("Out of memory for the data "
+				       "dictionary cache.");
+		}
+		assert(old_space_by_n == NULL || p_old_s == NULL);
+		if(old_space_by_n == NULL && p_old != NULL) {
+			assert(p_old->val == p_old_s->val);
+			old_space_by_n = (struct space *)p_old->val;
+		}
+		assert((struct space*)old_space_by_n == old_space);
 	} else {
 		mh_int_t k = mh_i32ptr_find(spaces, space_id(old_space), NULL);
 		assert(k != mh_end(spaces));
@@ -183,6 +229,14 @@ space_cache_replace(struct space *old_space, struct space *new_space)
 		(void)old_space_by_id;
 		assert(old_space_by_id == old_space);
 		mh_i32ptr_del(spaces, k, NULL);
+		const char *name = space_name(old_space);
+		k = mh_strnptr_find_inp(spaces_by_name, name, strlen(name));
+		assert(k != mh_end(spaces_by_name));
+		old_space_by_n = (struct space *)mh_strnptr_node(spaces_by_name,
+								 k)->val;
+		assert(old_space_by_n == old_space_by_id);
+		(void)old_space_by_id;
+		mh_strnptr_del(spaces_by_name, k, NULL);
 	}
 	space_cache_version++;
 }
@@ -302,6 +356,7 @@ schema_init()
 
 	/* Initialize the space cache. */
 	spaces = mh_i32ptr_new();
+	spaces_by_name = mh_strnptr_new();
 	funcs = mh_i32ptr_new();
 	funcs_by_name = mh_strnptr_new();
 	sequences = mh_i32ptr_new();
@@ -449,6 +504,7 @@ schema_free(void)
 		space_cache_replace(space, NULL);
 	}
 	mh_i32ptr_delete(spaces);
+	mh_strnptr_delete(spaces_by_name);
 	while (mh_size(funcs) > 0) {
 		mh_int_t i = mh_first(funcs);
 
diff --git a/src/box/schema.h b/src/box/schema.h
index 05f32de..89866a8 100644
--- a/src/box/schema.h
+++ b/src/box/schema.h
@@ -58,6 +58,14 @@ extern struct latch schema_lock;
 struct space *
 space_by_id(uint32_t id);
 
+/**
+ * Try to look up a space by space name in the space name cache.
+ *
+ * @return NULL if space not found, otherwise space object.
+ */
+struct space *
+space_by_name(const char *name);
+
 uint32_t
 box_schema_version();
 
-- 
2.11.0