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From Selcuk AYA <>
Subject Re: Txn Work Update(2)
Date Thu, 01 Dec 2011 07:37:49 GMT
On Wed, Nov 30, 2011 at 3:26 PM, Emmanuel Lecharny <> wrote:
> On 11/30/11 11:48 AM, Selcuk AYA wrote:
>> Hi all,
> hi !
>> time to give an update on the txn status. I just checked in some code
>> with explanation of the changes for each project separately. Here is
>> just an overall summary and todo:
>> *I added txn being/commit/abort to ldap requests and ran some test
>> with txns enabled. Put in various fixes to the txn layer based on the
>> tests. So first signs life signs for txns. More tests will be done but
>> I need to digress into AVL first. I also need to handle paged search.
> Great !
> Paged search is just a a normal search, but one that last longer. The way we
> handle it is by using a counter of sent responses.
> Basically, entries are sent one by one to the client, using a
> SearchResultEntry to hold the entry. With the pagedSearch, once we have
> reached the limit set by the client, we stop the sending of entries, and
> hold the cursor in the user's session, so that he can send back a new search
> request for then next entries - if needed -. Is there anything special you
> need to deal with here ? (btw, the cursor will be deleted as soon as the
> session will be closed. I hope this cleanup is effective...)
There is not much todo here as you guessed. The only problem is the
transaction context is stored in a thread local variable. When paged
search send partial data, we should store the context somewhere and
hand it off to the thread that will continue processing the search.

>> *I have also been working on removing interfaces related to
>> modification from the partition
> Hmmm, can you be a bit more specific ?

When I say modification or change, I mean
modify/move/rename/moveAndRename/add/delete. Instead of partitions
implementing these separately, there is a layer above partitions which
handle these operations transactionally. The class that handles this
is called OperationExecutionManager. Partitions expose master table
and indices for the operation execution manager execute the

>> and have been trying to get rid of the
>> Store interface. Got rid of the store interface except for config
>> methods and calls from the ui layer. I removed the modifications up
>> but still have to call the modification methods of the partition
>> interface because SchemaPartition triggers some changes based on the
>> logical  change. I believe those changes can be removed to schema
>> interceptor?
> We can't modify a schema. We can only add or delete a schema entry. This is
> a limitation, and I think it's mandated by the spec (don't remember where it
> comes from, but the idea is that modifying a schema element might imply a
> global modification on all the entries, something we don't want to accept).
>> In general, if a partition wants to do a change based on
>> a data update, then it should be able to do it during master table
>> update or by registering an interceptor(For example I changed multi
>> file ldif partition to do file updates when master table is updated).
>> Then we can get rid of the modification methods on partitions.
> you mean, the modify/move/rename/moveAndRename methods ?

As mentioned above, by change or modification, I mean any operation
that ends up in update of data. For schema partitions, I believe
changes triggered after logical ldap change operations can be moved to
an interceptor.

>> Note that, how search is done is still upto the partiton.
>> DefaultSearchEngine is changed to work with any partition and returns
>> transactioanally consistent data.( it used to work with Store
>> interface. Now it works with Partition interface. ). However, a
>> partition can use another search engine and can use the data in txn
>> logs to provide consistent data.
> Ok.
>> * Would be good to get triggers working as they are a nice way to
>> demonstrate txns. What is the reason trigger tests are ignored?
> Because since we have modified the server to not use JNDI anymore, it
> impacted the trigger code (which is still based on JNDI). We don't have time
> now to fix this feature, and we have to review the full code in this area,
> as the guy who contributed it is now gone and missing. Let's say it was a
> choice : we know that it's a cool feature, but it's not an urgent one atm...
>> * Would be good to have statement snapshot isolation for
>> EntryFilteringCursor. Not having this doesnt affect ldap requests but
>> might affect code that works with EntryFilteringCursor directly.
>> Currently there are few cases of this especially during startup.
> I'll buy some more explanation : what is a 'statement snapshot' ?

Say you do a search and get an entry filtering cursor and then you
modify the entries that you get from the cursor. Something like this:

cursor = ..
while ( )
  entry = cursor.get();
  modify entry.


If we have statement snapshot for the search, cursor will not see any
updates to the master table of index tables done through the
modifications.  This might be useful in some cases.

>> * Tried to introduce some rules into how modifications are done: If we
>> think of search engine and data modification layer as a data layer,
>> then under it we have storage level. Storage level might have a cache
>> of entries, or index entries or tuples. When a thread reads an object
>> from the storage layer and wants to update it, another thread might be
>> reading the same object. To avoid confusing the reader thread, object
>> to be changed should be cloned before change is applied.
> Absolutely.
>> Changed
>> modification layer to follow this rule. As mentioned in the previous
>> emails, default search engine is modifying index entries and this is
>> not good, I  put a workaround for this.
> Ok. We need to fix this.
> Thanks a lot for the update, Selcuk !
> --
> Regards,
> Cordialement,
> Emmanuel Lécharny

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