[tarantool-patches] Re: [PATCH 1/4] sql: optimize compilation of SELECT COUNT(*)

[n.pettik]

I have rebased on fresh 2.0, but no significant changes seem to appear.

> 1. In Tarantool 'memtx' count() is not a scan - it is O(1) operation, that simply
> gets current size of the primary index B+ tree. Maybe worth show it in the
> explanation.

Done (alongside, with tests):

 --- a/src/box/sql/select.c
+++ b/src/box/sql/select.c
@@ -5259,6 +5259,8 @@ updateAccumulator(Parse * pParse, AggInfo * pAggInfo)
 /**
  * Add a single OP_Explain instruction to the VDBE to explain
  * a simple count(*) query ("SELECT count(*) FROM <tab>").
+ * For memtx engine count is a simple operation,
+ * which takes O(1) complexity.
  *
  * @param parse_context Current parsing context.
  * @param table_name Name of table being queried.
@@ -5267,7 +5269,7 @@ static void
 explain_simple_count(struct Parse *parse_context, const char *table_name)
 {
        if (parse_context->explain == 2) {
-               char *zEqp = sqlite3MPrintf(parse_context->db, "SCAN TABLE %s",
+               char *zEqp = sqlite3MPrintf(parse_context->db, "B+tree count %s”,

==============================================================================

diff --git a/test/sql-tap/eqp.test.lua b/test/sql-tap/eqp.test.lua
index 468bca0a7..15d428814 100755
--- a/test/sql-tap/eqp.test.lua
+++ b/test/sql-tap/eqp.test.lua
@@ -733,10 +733,10 @@ test:do_execsql_test(
     ]])
 
 test:do_eqp_test(7.1, "SELECT count(*) FROM t1", {
-    {0, 0, 0, "SCAN TABLE T1"},
+    {0, 0, 0, "B+tree count T1"},
 })
 test:do_eqp_test(7.2, "SELECT count(*) FROM t2", {
-    {0, 0, 0, "SCAN TABLE T2"},
+    {0, 0, 0, "B+tree count T2"},
 })
 -- MUST_WORK_TEST
 if (0 > 0)
@@ -781,7 +781,7 @@ test:do_eqp_test("8.1.1", "SELECT * FROM t2", {
 --     {0, 0, 0, "SEARCH TABLE T2 USING INTEGER PRIMARY KEY (rowid=?)"},
 -- }
 test:do_eqp_test("8.1.3", "SELECT count(*) FROM t2", {
-    {0, 0, 0, "SCAN TABLE T2"},
+    {0, 0, 0, "B+tree count T2"},
 })
 test:do_eqp_test("8.2.1", "SELECT * FROM t1", {
     {0, 0, 0, "SCAN TABLE T1"},
@@ -793,7 +793,7 @@ test:do_eqp_test("8.2.3", "SELECT * FROM t1 WHERE b=? AND c=?", {
     {0, 0, 0, "SEARCH TABLE T1 USING PRIMARY KEY (B=? AND C=?)"},
 })
 test:do_eqp_test("8.2.4", "SELECT count(*) FROM t1", {
-    {0, 0, 0, "SCAN TABLE T1"},
+    {0, 0, 0, "B+tree count T1"},
 })