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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.
parent ad4da535
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Showing with 145 additions and 27 deletions
mysql-test/r/query_cache.result
View file @ b9dc6ad7
......@@ -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;
mysql-test/t/query_cache.test
View file @ b9dc6ad7
......@@ -1000,3 +1000,48 @@ set GLOBAL query_cache_min_res_unit=default;
set GLOBAL query_cache_size= default;
# End of 5.0 tests
#
# Bug #28211 RENAME DATABASE and query cache don't play nicely together
#
--disable_warnings
drop database if exists db1;
drop database if exists db2;
--enable_warnings
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;
show status like 'Qcache_queries_in_cache';
rename schema db1 to db2;
show status like 'Qcache_queries_in_cache';
drop database db2;
set global query_cache_size=default;
--disable_warnings
drop database if exists db1;
drop database if exists db3;
--enable_wearnings
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;
select c1+1 from db1.t1;
select * from db3.t1;
show status like 'Qcache_queries_in_cache';
rename schema db1 to db2;
show status like 'Qcache_queries_in_cache';
drop database db2;
drop database db3;
# End of 5.1 tests
sql/sql_cache.cc
View file @ b9dc6ad7
......@@ -1445,40 +1445,62 @@ void Query_cache::invalidate(THD *thd, const char *key, uint32 key_length,
DBUG_VOID_RETURN;
}
/*
Remove all cached queries that uses the given database
/**
@brief Remove all cached queries that uses the given database
*/
void Query_cache::invalidate(char *db)
{
bool restart= FALSE;
DBUG_ENTER("Query_cache::invalidate (db)");
STRUCT_LOCK(&structure_guard_mutex);
if (query_cache_size > 0 && !flush_in_progress)
{
DUMP(this);
restart_search:
if (tables_blocks)
{
Query_cache_block *curr= tables_blocks;
Query_cache_block *next;
do
{
next= curr->next;
if (strcmp(db, (char*)(curr->table()->db())) == 0)
invalidate_table(curr);
Query_cache_block *table_block = tables_blocks;
do {
restart= FALSE;
do
{
Query_cache_block *next= table_block->next;
Query_cache_table *table = table_block->table();
if (strcmp(table->db(),db) == 0)
invalidate_table(table_block);
table_block= next;
/*
If our root node to used tables became null then the last element
in the table list was removed when a query was invalidated;
Terminate the search.
*/
if (tables_blocks == 0)
{
table_block= tables_blocks;
}
/*
If the iterated list has changed underlying structure;
we need to restart the search.
*/
else if (table_block->type == Query_cache_block::FREE)
{
restart= TRUE;
table_block= tables_blocks;
}
/*
The used tables are linked in a circular list;
loop until we return to the begining.
*/
} while (table_block != tables_blocks);
/*
invalidate_table can freed block on which point 'next' (if
table of this block used only in queries which was deleted
by invalidate_table). As far as we do not allocate new blocks
and mark all headers of freed blocks as 'FREE' (even if they are
merged with other blocks) we can just test type of block
to be sure that block is not deleted
Invalidating a table will also mean that all cached queries using
this table also will be invalidated. This will in turn change the
list of tables associated with these queries and the linked list of
used table will be changed. Because of this we might need to restart
the search when a table has been invalidated.
*/
if (next->type == Query_cache_block::FREE)
goto restart_search;
curr= next;
} while (curr != tables_blocks);
}
} while (restart);
} // end if( tables_blocks )
}
STRUCT_UNLOCK(&structure_guard_mutex);
......@@ -2412,6 +2434,7 @@ Query_cache::register_tables_from_list(TABLE_LIST *tables_used,
(ulong) tables_used->table,
tables_used->table->s->table_cache_key.length,
(ulong) tables_used->table->s->table_cache_key.str));
if (!insert_table(tables_used->table->s->table_cache_key.length,
tables_used->table->s->table_cache_key.str,
block_table,
......@@ -2478,9 +2501,8 @@ my_bool Query_cache::register_all_tables(Query_cache_block *block,
n= register_tables_from_list(tables_used, 0, block_table);
if (n)
if (n==0)
{
DBUG_PRINT("qcache", ("failed at table %d", (int) n));
/* Unlink the tables we allocated above */
for (Query_cache_block_table *tmp = block->table(0) ;
tmp != block_table;
......@@ -2970,8 +2992,11 @@ Query_cache::double_linked_list_exclude(Query_cache_block *point,
{
point->next->prev = point->prev;
point->prev->next = point->next;
/*
If the root is removed; select a new root
*/
if (point == *list_pointer)
*list_pointer = point->next;
*list_pointer= point->next;
}
DBUG_VOID_RETURN;
}
......@@ -3769,7 +3794,7 @@ void Query_cache::tables_dump()
Query_cache_table *table = table_block->table();
DBUG_PRINT("qcache", ("'%s' '%s'", table->db(), table->table()));
table_block = table_block->next;
} while ( table_block != tables_blocks);
} while (table_block != tables_blocks);
}
else
DBUG_PRINT("qcache", ("no tables in list"));
......
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