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该Bug在MySQL的内部版本号为bug13943231，并且很容易触发该BUG
1.Test case：
create table t1(c1 int) engine=innodb;
alter table t1 discard tablespace;
alter table t1 add unique index(c1);
2.原因：
MySQL的discard tablespace操作实际上已经删除了.ibd文件，但在innodb层并没有判断该行为，而是继续执行下去，因此很快就触发断言失败，以下是一次crash的backtrace：
(gdb) f 2
#2 0x000000000089a39b in fil_space_get_latch (id=5988266, flags=0x4a20ed20)
at /home/yinfeng.zwx/project/PS5518/trunk/Percona-Server-5.5.18/storage/innobase/fil/fil0fil.c:537
537 ut_a(space);
(gdb) l
532
533 mutex_enter(&fil_system->mutex);
534
535 space = fil_space_get_by_id(id);
536
537 ut_a(space);
538
539 if (flags) {
540 *flags = space->flags;
541 }
(gdb) p space
$1 = (fil_space_t *) 0x0
#2 fil_space_get_latch
#3 fseg_create_general
#4 btr_create
#5 dict_create_index_tree_step
#6 dict_create_index_step
#7 que_thr_step
#8 que_run_threads_low
#9 que_run_threads
#10 row_merge_create_index_graph
#11 row_merge_create_index
#12 ha_innobase::add_index
3.修复(来自官方)：
修复的方法很简单，就是在add_index时判断是否已经discard tablespace了，如果是，就返回错误。
=== modified file ‘storage/innobase/handler/handler0alter.cc’
— storage/innobase/handler/handler0alter.cc 2012-02-28 12:04:21 +0000
+++ storage/innobase/handler/handler0alter.cc 2012-05-16 11:03:22 +0000
@@ -708,6 +708,10 @@
ut_a(indexed_table == prebuilt->table);
+ if (indexed_table->tablespace_discarded) {
+ DBUG_RETURN(-1);
+ }
+
/* Check that index keys are sensible */
error = innobase_check_index_keys(key_info, num_of_keys, prebuilt->table);
