Fix crash in embedded server due to incorrect storage of results

in the query cache. (Bug #9549)


libmysqld/emb_qcache.h:
  Fix Querycache_stream::use_next_block() to actually use the next
  block and mark blocks as used when it writes to them.
mysql-test/r/query_cache.result:
  Update results.
mysql-test/t/query_cache.test:
  Add new regression test.
libmysqld/emb_qcache.cc:
  Fix calls to use_next_block() to indicate whether we are writing
  to the next block or not.
sql/sql_cache.cc:
  Initialize the first block properly when storing a result in
  the embedded server.

1 files changed, 45 insertions, 0 deletions

diff --git a/mysql-test/t/query_cache.test b/mysql-test/t/query_cache.test
index b0148a689af..b287e71d6ae 100644
--- a/mysql-test/t/query_cache.test
+++ b/mysql-test/t/query_cache.test
@@ -684,4 +684,49 @@ repair table t1;
 show status like 'qcache_queries_in_cache';
 drop table t1;
 
+# Bug #9549: Make sure cached queries that span more than one cache block
+# are handled properly in the embedded server.
+
+# We just want a small query cache, so we can fragment it easily
+set GLOBAL query_cache_size=64*1024;
+# This actually gives us a usable cache size of about 48K
+
+# Each table is about 14K
+create table t1 (a text);
+insert into t1 values (repeat('abcdefghijklmnopqrstuvwxyz', 550));
+create table t2 (a text);
+insert into t2 values (repeat('ijklmnopqrstuvwxyzabcdefgh', 550));
+
+# Load a query from each table into the query cache
+--disable_result_log
+select a from t1; # Q1
+select a from t2; # Q2
+--enable_result_log
+show status like 'Qcache_%_blocks';
+
+# Now the cache looks like (14K for Q1)(14K for Q2)(20K free)
+
+# Flush Q1 from the cache by adding an out-of-order chunk to t1
+insert into t1 select reverse(a) from t1;
+show status like 'Qcache_%_blocks';
+
+# Now the cache looks like (14K free)(14K for Q2)(20K free)
+
+# Load our new data into the query cache
+--disable_result_log
+select a from t1;  # Q3
+--enable_result_log
+show status like 'Qcache_%_blocks';
+
+# Now the cache should be like (14K for Q3)(14K for Q2)(14K for Q3)(6K free)
+
+# Note that Q3 is split across two chunks!
+
+# Load Q3 from the cache, and actually pay attention to the results
+select a from t1;
+
+flush query cache;
+
+drop table t1, t2;
+
 set GLOBAL query_cache_size=0;