Cursor::doStartTableScan can be called twice without any cleanup

[Stewart Smith]

first select query in count_distinct.

hit assert in libinnodb with embedded_innodb engine.

Breakpoint 1, drizzled::mysql_parse (session=0x14e0f10,
    inBuf=0x14de808 "drop table if exists t1,t2,t3", length=29)
    at drizzled/sql_parse.cc:715
715 lex_start(session);
(gdb) b EmbeddedInnoDBCursor::doStartTableScan(bool)
Breakpoint 2 at 0x7ffff3f2e9d8: file plugin/embedded_innodb/embedded_innodb_engine.cc, line 1735.
(gdb) c
Continuing.

Breakpoint 2, EmbeddedInnoDBCursor::doStartTableScan (this=0x14f7268)
    at plugin/embedded_innodb/embedded_innodb_engine.cc:1735
1735 if(*get_trx(current_session) == NULL)
(gdb) b EmbeddedInnoDBCursor::doEndTableScan()
Breakpoint 3 at 0x7ffff3f2efee: file plugin/embedded_innodb/embedded_innodb_engine.cc, line 1860.
(gdb) b EmbeddedInnoDBCursor::close()
Breakpoint 4 at 0x7ffff3f2b6b6: file plugin/embedded_innodb/embedded_innodb_engine.cc, line 628.
(gdb) b EmbeddedInnoDBCursor::reset()
Breakpoint 5 at 0x7ffff3f2fe12: file plugin/embedded_innodb/embedded_innodb_engine.cc, line 2221.
(gdb) c
Continuing.

Breakpoint 2, EmbeddedInnoDBCursor::doStartTableScan (this=0x14f7268)
    at plugin/embedded_innodb/embedded_innodb_engine.cc:1735
1735 if(*get_trx(current_session) == NULL)
(gdb)

[Stewart Smith (stewart)]

=== modified file 'plugin/embedded_innodb/embedded_innodb_engine.cc'
--- plugin/embedded_innodb/embedded_innodb_engine.cc 2010-05-26 10:19:08 +0000
+++ plugin/embedded_innodb/embedded_innodb_engine.cc 2010-05-26 13:14:09 +0000
@@ -620,6 +620,8 @@
     ref_length= 0; // FIXME: this is a bug. we need to work out what index it is.
   }

+ in_table_scan= false;
+
   return(0);
 }

@@ -1732,6 +1734,10 @@
 {
   ib_trx_t transaction;

+ if (in_table_scan)
+ doEndTableScan();
+ in_table_scan= true;
+
   if(*get_trx(current_session) == NULL)
   {
     EmbeddedInnoDBEngine *innodb_engine= static_cast<EmbeddedInnoDBEngine*>(engine);
@@ -1859,7 +1865,7 @@
   ib_tuple_delete(tuple);
   err= ib_cursor_reset(cursor);
   assert(err == DB_SUCCESS);
-
+ in_table_scan= false;
   return 0;
 }
You need to do something like this:

=== modified file 'plugin/embedded_innodb/embedded_innodb_engine.h'
--- plugin/embedded_innodb/embedded_innodb_engine.h 2010-05-26 10:19:08 +0000
+++ plugin/embedded_innodb/embedded_innodb_engine.h 2010-05-26 13:14:09 +0000
@@ -123,6 +123,8 @@
   bool write_can_replace;
   uint64_t hidden_autoinc_pkey_position;
   drizzled::memory::Root *blobroot;
+
+ bool in_table_scan;
 };

 #endif /* PLUGIN_EMBEDDED_INNODB_EMBEDDED_INNODB_ENGINE_H */

[Stewart Smith (stewart)]

What you know (from http://forge.mysql.com/wiki/MySQL_Internals_Custom_Engine#14.17.21.rnd_init):

Unlike index_init(), rnd_init() can be called two times without rnd_end() in between (it only makes sense if scan=1). then the second call should prepare for the new table scan (e.g if rnd_init allocates the cursor, second call should position it to the start of the table, no need to deallocate and allocate it again

Actually documented.

Index scanning has index_first()... why we couldn't have something sane ,who knows.

We should still fix it.