Bug #19773 Crash when using multi-table updates with federated tables
Submitted: 12 May 2006 14:50 Modified: 13 Jul 2006 3:48
Reporter: Michael Widenius Email Updates:
Status: Closed Impact on me:
None 
Category:MySQL Server: Federated storage engine Severity:S1 (Critical)
Version:5.0.22, 5.1.10 OS:Linux (Linux)
Assigned to: Bugs System CPU Architecture:Any

[12 May 2006 14:50] Michael Widenius
Description:
The implementations of ha_federated::position() and ha_federarated::rnd_pos() are conceptually wrong and needs to be re-implented.

The idea of ::postition() is that it should return a reference (primary key, cursor position, file position, etc) to a given row so that on can use ::rnd_pos() to retrive the same row again.

The current implementations assumes that the row is in the active result set, but this is not the case and that why we get a crash.

How to repeat:
Save the file federated2.test as t/federated2.test and do:
mysql-test-run --record t/federated2.test

Note that the test result federated2.result doesn not 100 % comply to federated2.test
The reason is that as federated2.test crashed, I was not able to create a correct result file but instead did run the test against a MyISAM table.

The results from the queries should however be correct and should help verify that the federated code is fixed correctly 

Suggested fix:
The code should be fixed in the following way:

- Rewrite ::position() so that if we are doing a table scan, then store the internal position in *ref. If not, then store the primary key in *ref'.  :rnd_pos() should detect what is stored in *pos and use either position or primary key to find the row.

If there is no primary key, don't allow this table to be updated in a multi-table-update.
[12 May 2006 14:51] Michael Widenius
Test case for bug

Attachment: federated2.test (application/octet-stream, text), 2.42 KiB.

[12 May 2006 14:51] Michael Widenius
Result set for test case (with MyISAM files instead of federated files)

Attachment: federated2.result (application/octet-stream, text), 1.60 KiB.

[17 May 2006 22:40] Patrick Galbraith
Working on a solution for ::position
[26 May 2006 23:45] Patrick Galbraith
this is what I have so far. It passes the basic federated test, but still no go on federated2

void ha_federated::position(const byte *record)
{
  DBUG_ENTER("ha_federated::position");
  if (has_a_primary_key)
  {
    DBUG_PRINT("info", ("has_a_primary_key"));
    ref_length= table->key_info[0].key_length;
    key_copy(ref, (byte *)record, table->key_info, ref_length);
  }
  else
  {
    DBUG_PRINT("info", ("has_a_primary_key"));
    ref_length= mean_rec_length;
    memcpy(ref, record, ref_length);
  }
  DBUG_VOID_RETURN;
}

int ha_federated::rnd_pos(byte *buf, byte *pos)
{
  DBUG_ENTER("ha_federated::rnd_pos");

  int result= 0;
  statistic_increment(table->in_use->status_var.ha_read_rnd_count,
                      &LOCK_status);
  if (has_a_primary_key)
    result= index_read_idx(buf, 0, pos, ref_length, HA_READ_KEY_EXACT);
  else
    memcpy(buf, pos, ref_length);
  DBUG_RETURN(result);
}
[1 Jun 2006 16:09] Patrick Galbraith
Further help from Antony has yielded a working solution that I am working on coding. I estimate this to be committed for review in a day.
[7 Jun 2006 16:27] Patrick Galbraith
I have working code that I just need to clean up today and hope to have a commit for review by end of day.
[8 Jun 2006 14:09] Patrick Galbraith
See patch
[21 Jun 2006 12:27] Michael Widenius
Review done.
- Some part of patch needs to be moved into 5.1 as this is new optimizations
- A lot of cleanups to do
[22 Jun 2006 6:38] Bugs System
A patch for this bug has been committed. After review, it may
be pushed to the relevant source trees for release in the next
version. You can access the patch from:

  http://lists.mysql.com/commits/8049
[28 Jun 2006 6:43] Bugs System
A patch for this bug has been committed. After review, it may
be pushed to the relevant source trees for release in the next
version. You can access the patch from:

  http://lists.mysql.com/commits/8375
[28 Jun 2006 10:00] Michael Widenius
Created a new patch based on Patricks patch, but with less overall code changes.
Patrick has the patch and for me it's ok to push that patch.
[28 Jun 2006 19:11] Bugs System
A patch for this bug has been committed. After review, it may
be pushed to the relevant source trees for release in the next
version. You can access the patch from:

  http://lists.mysql.com/commits/8431
[3 Jul 2006 5:11] Bugs System
A patch for this bug has been committed. After review, it may
be pushed to the relevant source trees for release in the next
version. You can access the patch from:

  http://lists.mysql.com/commits/8628
[6 Jul 2006 19:26] Paul Dubois
Noted in 5.0.23 changelog.

Multiple-table updates with FEDERATED tables could cause a server crash.
[11 Jul 2006 18:35] Patrick Galbraith
Ver 5.1.12-beta
[13 Jul 2006 3:48] Paul Dubois
Noted in 5.1.12 changelog.
[13 Jul 2006 22:09] Bugs System
A patch for this bug has been committed. After review, it may
be pushed to the relevant source trees for release in the next
version. You can access the patch from:

  http://lists.mysql.com/commits/9144
[13 Jul 2006 22:09] Bugs System
A patch for this bug has been committed. After review, it may
be pushed to the relevant source trees for release in the next
version. You can access the patch from:

  http://lists.mysql.com/commits/9145