MDEV-31787 MDEV-26151 Add a test exercising non-0 spider_casual_read

Also:
- clean up spider_check_and_get_casual_read_conn() and
  spider_check_and_set_autocommit()
- remove a couple of commented out code blocks

storage/spider/mysql-test/spider/bugfix/r/mdev_26151.result

+
+MDEV-26151 MDEV-31787
+
+for master_1
+for child2
+for child3
+set @old_spider_bgs_mode= @@spider_bgs_mode;
+set session spider_bgs_mode=1;
+CREATE SERVER $srv FOREIGN DATA WRAPPER MYSQL OPTIONS (SOCKET "$MASTER_1_MYSOCK", DATABASE 'test',user 'root');
+create table td (a int, PRIMARY KEY (a));
+create table ts (a int, PRIMARY KEY (a)) ENGINE=Spider COMMENT='WRAPPER "mysql", srv "srv_mdev_26151",TABLE "td", casual_read "3"';
+insert into td values (11), (42);
+select max(a) from ts;
+max(a)
+42
+drop table td, ts;
+create table td (a int, PRIMARY KEY (a));
+create table ts (a int, PRIMARY KEY (a)) ENGINE=Spider COMMENT='WRAPPER "mysql", srv "srv_mdev_26151",TABLE "td", casual_read "1"';
+insert into td values (11), (42);
+select max(a) from ts;
+max(a)
+42
+select min(a) from ts;
+min(a)
+11
+drop table td, ts;
+drop server srv_mdev_26151;
+set session spider_bgs_mode=@old_spider_bgs_mode;
+for master_1
+for child2
+for child3
+
+end of test
+

storage/spider/mysql-test/spider/bugfix/t/mdev_26151.test

+--echo
+--echo MDEV-26151 MDEV-31787
+--echo
+
+# This test exercises the code path where a nonzero casual_read takes
+# effect.
+
+--disable_query_log
+--disable_result_log
+--source ../../t/test_init.inc
+--enable_result_log
+--enable_query_log
+
+--let $srv=srv_mdev_26151
+set @old_spider_bgs_mode= @@spider_bgs_mode;
+set session spider_bgs_mode=1;
+evalp CREATE SERVER $srv FOREIGN DATA WRAPPER MYSQL OPTIONS (SOCKET "$MASTER_1_MYSOCK", DATABASE 'test',user 'root');
+
+# casual_read != 0 && casual_read != 1
+create table td (a int, PRIMARY KEY (a));
+
+eval create table ts (a int, PRIMARY KEY (a)) ENGINE=Spider COMMENT='WRAPPER "mysql", srv "$srv",TABLE "td", casual_read "3"';
+
+insert into td values (11), (42);
+
+select max(a) from ts;
+
+drop table td, ts;
+
+create table td (a int, PRIMARY KEY (a));
+
+# casual_read = 1
+eval create table ts (a int, PRIMARY KEY (a)) ENGINE=Spider COMMENT='WRAPPER "mysql", srv "$srv",TABLE "td", casual_read "1"';
+
+insert into td values (11), (42);
+
+select max(a) from ts;
+
+select min(a) from ts;
+
+drop table td, ts;
+
+eval drop server $srv;
+set session spider_bgs_mode=@old_spider_bgs_mode;
+
+--disable_query_log
+--disable_result_log
+--source ../../t/test_deinit.inc
+--enable_result_log
+--enable_query_log
+
+--echo
+--echo end of test
+--echo

storage/spider/spd_conn.cc

@@ -1260,6 +1260,30 @@ int spider_free_conn(
   DBUG_RETURN(0);
 }
 
+/**
+  May get or create a connection spawning a background thread
+
+  For each link (data node, formally representable as the tuple
+  (spider, link_idx)), there is an associated casual read value
+  (`spider->result_list.casual_read[link_idx]').
+
+  If the CRV is 0, do nothing. Otherwise, An casual read id
+  (`conn->casual_read_current_id`) is associated with the link and
+  query id. The CRI starts from 2, and is used only when CRV is 1, to
+  update the CRV (see below). The updated CRV is then used to
+  construct the connection key used for get or create a connection
+  that spawns a background thread to execute queries.
+
+  If the CRV is 1, it is assigned CRI. The latter is then incremented
+  by 1. The CRI will only go up to 63, before "wrapping" back to 2.
+
+  If 2 <= CRV <= 63, it is left alone.
+
+  Note that this function relies on the assumption that the CRV is
+  reset (e.g. using `spider_param_casual_read()') between consecutive
+  calls of this function for the CRV == 1 case to auto-increment as
+  expected.
+*/
 int spider_check_and_get_casual_read_conn(
   THD *thd,
   ha_spider *spider,
@@ -1267,8 +1291,8 @@ int spider_check_and_get_casual_read_conn(
 ) {
   int error_num;
   DBUG_ENTER("spider_check_and_get_casual_read_conn");
-  if (spider->result_list.casual_read[link_idx])
-  {
+  if (!spider->result_list.casual_read[link_idx])
+    DBUG_RETURN(0);
   SPIDER_CONN *conn = spider->conns[link_idx];
   if (conn->casual_read_query_id != thd->query_id)
   {
@@ -1280,28 +1304,22 @@ int spider_check_and_get_casual_read_conn(
     spider->result_list.casual_read[link_idx] = conn->casual_read_current_id;
     ++conn->casual_read_current_id;
     if (conn->casual_read_current_id > 63)
-      {
       conn->casual_read_current_id = 2;
   }
-    }
   char first_byte_bak = *spider->conn_keys[link_idx];
   *spider->conn_keys[link_idx] =
     '0' + spider->result_list.casual_read[link_idx];
-    if (
-      !(spider->conns[link_idx] =
-        spider_get_conn(spider->share, link_idx,
-          spider->conn_keys[link_idx], spider->trx,
-          spider, FALSE, TRUE, SPIDER_CONN_KIND_MYSQL,
-          &error_num))
-    ) {
+  if (!(spider->conns[link_idx]= spider_get_conn(
+          spider->share, link_idx, spider->conn_keys[link_idx],
+          spider->trx, spider, FALSE, TRUE, SPIDER_CONN_KIND_MYSQL,
+          &error_num)))
+  {
     *spider->conn_keys[link_idx] = first_byte_bak;
     DBUG_RETURN(error_num);
   }
   *spider->conn_keys[link_idx] = first_byte_bak;
   spider->conns[link_idx]->casual_read_base_conn = conn;
-    conn = spider->conns[link_idx];
-    spider_check_and_set_autocommit(thd, conn, NULL);
-  }
+  spider_check_and_set_autocommit(thd, spider->conns[link_idx], NULL);
   DBUG_RETURN(0);
 }
 
@@ -1837,6 +1855,12 @@ int spider_set_conn_bg_param(
   DBUG_RETURN(0);
 }
 
+/**
+  Creates a background thread on `conn' to run `spider_bg_conn_action()'
+
+  Does not create when `conn' is NULL or a bg thread has already been
+  created for `conn'.
+*/
 int spider_create_conn_thread(
   SPIDER_CONN *conn
 ) {

storage/spider/spd_trx.cc

@@ -1589,27 +1589,9 @@ int spider_check_and_set_autocommit(
   SPIDER_CONN *conn,
   int *need_mon
 ) {
-  bool autocommit;
   DBUG_ENTER("spider_check_and_set_autocommit");
-
-  autocommit = !thd_test_options(thd, OPTION_NOT_AUTOCOMMIT);
-  if (autocommit)
-  {
-    spider_conn_queue_autocommit(conn, TRUE);
-  } else {
-    spider_conn_queue_autocommit(conn, FALSE);
-  }
-/*
-  if (autocommit && conn->autocommit != 1)
-  {
-    spider_conn_queue_autocommit(conn, TRUE);
-    conn->autocommit = 1;
-  } else if (!autocommit && conn->autocommit != 0)
-  {
-    spider_conn_queue_autocommit(conn, FALSE);
-    conn->autocommit = 0;
-  }
-*/
+  spider_conn_queue_autocommit(
+    conn, !thd_test_options(thd, OPTION_NOT_AUTOCOMMIT));
   DBUG_RETURN(0);
 }
 
@@ -1631,17 +1613,6 @@ int spider_check_and_set_sql_log_off(
       spider_conn_queue_sql_log_off(conn, FALSE);
     }
   }
-/*
-  if (internal_sql_log_off && conn->sql_log_off != 1)
-  {
-    spider_conn_queue_sql_log_off(conn, TRUE);
-    conn->sql_log_off = 1;
-  } else if (!internal_sql_log_off && conn->sql_log_off != 0)
-  {
-    spider_conn_queue_sql_log_off(conn, FALSE);
-    conn->sql_log_off = 0;
-  }
-*/
   DBUG_RETURN(0);
 }