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From "Mike Matrigali (JIRA)" <j...@apache.org>
Subject [jira] Updated: (DERBY-2364) improve documentation to explain logged/unlogged operations
Date Sun, 06 May 2007 22:11:15 GMT

     [ https://issues.apache.org/jira/browse/DERBY-2364?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
]

Mike Matrigali updated DERBY-2364:
----------------------------------

      Component/s: Documentation
    Fix Version/s: 10.3.0.0

> improve documentation to explain logged/unlogged operations
> -----------------------------------------------------------
>
>                 Key: DERBY-2364
>                 URL: https://issues.apache.org/jira/browse/DERBY-2364
>             Project: Derby
>          Issue Type: Improvement
>          Components: Documentation
>            Reporter: Jim Newsham
>            Priority: Minor
>             Fix For: 10.3.0.0
>
>
> Documentation does not appear to describe what logged and unlogged operations are (definition,
description), nor which specific operations are logged and which are unlogged, under normal
circumstances.
> From derby-user mailing list discussion:
> Jim Newsham wrote:
> > I'd like to back up an online derby database, and would also like to 
> > understand how this interacts with other concurrent transactions 
> > (regarding visibility, blocking, etc.).  I found some documentation in 
> > derbyadmin.pdf.  It mentions logged and unlogged operations, but 
> > doesn't describe what they are, or which database operations are 
> > logged and which are unlogged.  Is there another reference that provides more details?
> > 
> Hi Jim,
> I am assuming you are referring to 10.2 version of the Derby. In 10.2 Backup does not
block any user operations (DML/DDL), it just makes any un-logged operation to a logged one
if an  unlogged operation starts after the backup starts copying data or waits if an unlogged
operation is in progress, if you use SYSCS_UTIL.SYSCS_BACKUP_DATABASE(). If you don't the
backup to wait for unlogged operation to complete, then you can use SYSCS_UTIL.SYSCS_BACKUP_DATABASE_NOWAIT.
These two methods are described in the admin guide: 
> http://db.apache.org/derby/docs/10.2/adminguide/cadminhubbkup01.html)
> The reason to do automatic conversion of  unlogged operation to logged 
> one or make backup wait is,   Derby backup relies on transaction log 
> to bring the database to consistent state using the data file copies.
>  From the user perspective some operations that are unlogged may run slow,because during
the backup they are getting logged; but they will not get blocked for the backup to complete.
> What are the unlogged operations in Derby ?
> Derby does not have support like unlogged tables , but internally for 
> some operations it does not log because it can keep the database 
> consistent without logging the data.
> I don't remember all the cases, but two main unlogged operations 
> cases, I know of are :
> 1) Index creation:
> Only "create index is logged" , but not all the data inserts into the 
> index. The reason inserts into the index on create is not logged is , 
> if there is a failure , it will just drop the index.
> If you create an index when the backup is in progress, it will be 
> slower because it has to be logged.
> Foreign Keys , Primary Keys create backing indexes. Adding those keys
> to an existing table with data  will also run slower.
> 2) Import to an empty table or replacing all the data in a table.
> In this case also data inserts into table are not logged.  Internally
> derby creates a new table for the import and changes the catalogs to
> point to the new table and drops the original table when import
> completes.
> If you perform such an import operation when backup is in progress ,
> it will be slower because data is logged.
> I thought some of these cases were mentioned in the docs, looks like
> they are not. Please file a Jira entry for the doc improvement.
> Hope that helps
> -suresh

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