[hibernate-issues] [Hibernate-JIRA] Updated: (HHH-2448) Generate identical column aliases among cluster

[Loïc LEFEVRE (JIRA)]

     [ http://opensource.atlassian.com/projects/hibernate/browse/HHH-2448?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

Loïc LEFEVRE updated HHH-2448:
------------------------------

    Attachment: report_03.txt

Okay after some more investigation, I can say that columns aliases are mainly compound of:
-1- the first letters -- including the '_' character or not (depends upon the version, commented right now) -- 
    of the column: if column.name = TOTO_OID keep only TOTO_ or TOTO so that the length of "TOTO" + uniqueInteger + "_" is 10 chars long
-2- the unique integer of the table the column belong to + a trailing '_' (the unique integer of the table is generated in the constuctor
    of the org.hibernate.mapping.Table class and depends of the mapping loading *order*
    
Whereas the attachment report_1.txt shows differences in columns aliases naming regarding the column unique integer, we decided to
load all the mappings at application starting so now the first unique integer "bug" is corrected. 

However we then encountered problems regarding the table unique number (see report_3.txt). And since this is caused by mapping load ordering, 
I checked our java code doing this job and found we first load all the mapping filenames in a HashSet and then we iterate on this to load all 
mappings using org.hibernate.cfg.Configuration.addClass() and I'm sure the HashSet is the cause of our problems. If I use a TreeSet, then the 
(same) mappings will be loaded in the same order on any application server instance of our cluster.

It seems these choices will (theoretically) prevent our problems but we'll try before saying so.

By the way, this can lead to a warning regarding mapping best practices in a cluster environment.

Regards,
Loïc

> Generate identical column aliases among cluster
> -----------------------------------------------
>
>                 Key: HHH-2448
>                 URL: http://opensource.atlassian.com/projects/hibernate/browse/HHH-2448
>             Project: Hibernate3
>          Issue Type: Improvement
>          Components: query-criteria, query-hql
>    Affects Versions: 3.2.2
>         Environment: Hibernate version: 3.2.2, 2.1.8
> Database: Oracle 9.2.0.8
>            Reporter: Loïc LEFEVRE
>         Attachments: report_03.txt, report_1.txt, report_2.txt
>
>
> Among our weblogic cluster (12 instances), we can see that a query can have different column aliases.
> Although all seems correct, when regarding database reports like StatsPack or Spotlight we can see that because of these different aliases, the reports are wrong. Indeed, a resource consuming query can see its associated report properties (cpu usage, buffer gets, number of executions...) divided by the number of weblogic instances of our cluster (i.e. divided by 12) thus preventing us to pinpoint the queries to look at.
> On a 3 instances cluster, we can see this report:
> REPORT#1: one statement with a poor number of buffer gets/execution is reported splitted in 3, see the alias generated for column DTO.CREATION_DATE
> for example
> On a 4 instances cluster, we can see this report:
> REPORT#2: one statement responsible of the latch free/cache buffers chains wait events splitted in 4, note the column alias generated fordeffcashcy0_.BEST_EXPECTED_CY
> More than confusing the DBAs about the same query with n different "faces", our reports don't show us all the queries to look at: indeed, in our "Top 50 queries", a lot of them are duplicates! Also the memory required in the SGA to store the queries, the execution plan and so on is increased...
> Finally, although the column aliases can have up to 30 characters under Oracle, the limit is set to 10, why? 

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