Bug#28211 RENAME DATABASE and query cache don't play nicely together

When all table blocks were removed from the query cache the client session
hung in a tight loop waiting on an impossible condition while consuming a lot
of CPU.

This patch also corrects an error which caused valid tables to sometimes be
removed from the query cache.


mysql-test/r/query_cache.result:
  Added test case to make sure server doesn't hang in a tight loop if last
  table block is removed from the cache.
mysql-test/t/query_cache.test:
  Added test case to make sure server doesn't hang in a tight loop if last
  table block is removed from the cache.
sql/sql_cache.cc:
  - Refactored loop over table blocks. The invalidate_table() function effects
    the elements over which we iterate. The previous stop condition was broken
    due to a compiler optimization error probably caused by the goto-statement
    pointing out of the loop. The effect being that tables_blocks was never
    checked for null values and thus the loop never terminated.
  - The new implementation uses two while loops instead of a goto-statement.
    The tables_blocks is a circular list which becomes null if the last table
    block is removed from the list.

1 files changed, 48 insertions, 0 deletions

diff --git a/mysql-test/r/query_cache.result b/mysql-test/r/query_cache.result
index 64d32ba334c..287ccd3e048 100644
--- a/mysql-test/r/query_cache.result
+++ b/mysql-test/r/query_cache.result
@@ -1437,3 +1437,51 @@ set GLOBAL query_cache_type=default;
 set GLOBAL query_cache_limit=default;
 set GLOBAL query_cache_min_res_unit=default;
 set GLOBAL query_cache_size= default;
+drop database if exists db1;
+drop database if exists db2;
+set GLOBAL query_cache_size=15*1024*1024;
+create database db1;
+use db1;
+create table t1(c1 int)engine=myisam;
+insert into t1(c1) values (1);
+select * from db1.t1 f;
+c1
+1
+show status like 'Qcache_queries_in_cache';
+Variable_name	Value
+Qcache_queries_in_cache	1
+rename schema db1 to db2;
+show status like 'Qcache_queries_in_cache';
+Variable_name	Value
+Qcache_queries_in_cache	0
+drop database db2;
+set global query_cache_size=default;
+drop database if exists db1;
+drop database if exists db3;
+set GLOBAL query_cache_size=15*1024*1024;
+create database db1;
+create database db3;
+use db1;
+create table t1(c1 int) engine=myisam;
+use db3;
+create table t1(c1 int) engine=myisam;
+use db1;
+insert into t1(c1) values (1);
+use mysql;
+select * from db1.t1;
+c1
+1
+select c1+1 from db1.t1;
+c1+1
+2
+select * from db3.t1;
+c1
+show status like 'Qcache_queries_in_cache';
+Variable_name	Value
+Qcache_queries_in_cache	3
+rename schema db1 to db2;
+show status like 'Qcache_queries_in_cache';
+Variable_name	Value
+Qcache_queries_in_cache	1
+drop database db2;
+drop database db3;