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From Bart van der Schans <b.vandersch...@onehippo.com>
Subject Re: Question about consistency checker and node ordering in queries
Date Fri, 20 Jan 2012 14:44:25 GMT
On Fri, Jan 20, 2012 at 3:39 PM, Julian Reschke <julian.reschke@gmx.de> wrote:
> On 2012-01-20 15:22, Bart van der Schans wrote:
>>
>> Hi all,
>>
>> I was wondering about how the ConsistencyCheckerImpl fetches all the
>> node ids. The first set of node ids is fetched with
>> "pm.getAllNodeIds(null, NODESATONCE)" in the internalCheckConsistency
>> method. All subsequent sets are fetched with "pm.getAllNodeIds(lastId,
>> NODESATONCE)".
>>
>> In the BundleDbPersistenceManager the method
>> getAllNodeIds(NodeId,maxCount) uses the "bundleSelectAllIdsSQL" if the
>> first parameter is null otherwise the "bundleSelectAllIdsFromSQL"
>> query. The  "bundleSelectAllIdsSQL" query doesn't use ordering and the
>> "bundleSelectAllIdsFromSQL" does.
>>
>> Now my question is the following: souldn't the "bundleSelectAllIdsSQL"
>> also use an order clause to make sure the correct batch of node ids is
>> fetched the first time? Or is that somehow implicitly guaranteed?
>
>
> Good question. I was confused about that as well. I tried and stepped
> through he code and everything seem to worked as advertised, so I stopped
> worrying about it :-)

I think (at least on mysql) we're just lucky that the natural ordering
is by NODE_ID:

mysql> SELECT hex(NODE_ID) FROM VERSION_BUNDLE ORDER BY NODE_ID LIMIT 0,10;
+----------------------------------+
| hex(NODE_ID)                     |
+----------------------------------+
| 000005E87E6D402BA27CDF41E7999D8A |
| 000007DC02CF48BA8FFEDA5F566A3A98 |
| 00000C4A81744934B4F0CB55C9967378 |
| 000016C9E4464C4FA7B6F4B9CF2F9903 |
| 00001D5A1C6F4339B317BB436AA54431 |
| 0000257D67AB4F1EA4DDEDB84BB13039 |
| 00002C51F22145B89F59E882BB505036 |
| 00002F2AFC2E4842863C360B68A36BDA |
| 0000354F151945CEA953D62C922A4FAC |
| 00003C0254C8471E8349C0B6F0DEFDC2 |
+----------------------------------+
10 rows in set (0.00 sec)

mysql> SELECT hex(NODE_ID) FROM VERSION_BUNDLE LIMIT 0,10;
+----------------------------------+
| hex(NODE_ID)                     |
+----------------------------------+
| 000005E87E6D402BA27CDF41E7999D8A |
| 000007DC02CF48BA8FFEDA5F566A3A98 |
| 00000C4A81744934B4F0CB55C9967378 |
| 000016C9E4464C4FA7B6F4B9CF2F9903 |
| 00001D5A1C6F4339B317BB436AA54431 |
| 0000257D67AB4F1EA4DDEDB84BB13039 |
| 00002C51F22145B89F59E882BB505036 |
| 00002F2AFC2E4842863C360B68A36BDA |
| 0000354F151945CEA953D62C922A4FAC |
| 00003C0254C8471E8349C0B6F0DEFDC2 |
+----------------------------------+
10 rows in set (0.00 sec)

But that doesn't have to be the case with other databases. Maybe
somebody can try similar queries on another database?

Regards,
bart

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