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From "Sunitha Kambhampati (JIRA)" <derby-...@db.apache.org>
Subject [jira] Commented: (DERBY-271) Document the new property derby.system.durability=test
Date Tue, 17 May 2005 00:10:05 GMT
     [ http://issues.apache.org/jira/browse/DERBY-271?page=comments#action_65573 ]
     
Sunitha Kambhampati commented on DERBY-271:
-------------------------------------------

Thanks Jeff for quickly generating the doc.
Here are some of my comments.  Thanks.
------------------------

This is a property that can take values other than test, but currently we only support 'test'
but in future will be used for other durability modes.
Therefore I dont think we should say ' This property can be used under testing purposes to
improve performance'     but maybe instead to say something similar to

This property can be used to change the default durability of derby to improve performance
at the expense of consistency and durability of the database.
Currently the only valid supported case insensitive value is 'test'.  If this property is
set to any other value other than 'test', this property setting is ignored
In the future, this property can be used to set different modes of durability - for example
a form of relaxed durability where database can recover to a
consistent state, or to enable some kind of in-memory mode.

1) I think we need to specify that the supported value is test  , maybe after 'Default' section
.
Supported values are 'test'

2)  This line needs to change 'Consequently, this property should only be set when using Derby
as a test database, where high performance is required and the data is not very important.'
Since users can use it for whatever they want as long as they can withstand the consequences
of using derby.system.durability=test.   So how about we change this to say a sample usage
would be to enable this property when using Derby as a test database where consistency or
recoverability is not an issue. It could probably go along in the example section.

> Document the new property derby.system.durability=test
> ------------------------------------------------------
>
>          Key: DERBY-271
>          URL: http://issues.apache.org/jira/browse/DERBY-271
>      Project: Derby
>         Type: Sub-task
>   Components: Documentation
>     Versions: 10.1.0.0
>     Reporter: Sunitha Kambhampati
>     Assignee: Jeff Levitt
>  Attachments: derby271new.zip
>
> Need to document the new property - derby.system.durability
> This should probably go along with other properties in Tuning guide. 
> --------------------------------------------------    
> derby.system.durability
> Currently the only valid supported case insensitive value is 'test' 
> If this property is set to any other value other than 'test', this 
> property setting is ignored
> In the future, this property can be used to set different modes of durability 
> - for example a form of relaxed durability where database can recover to a 
> consistent state, or to enable some kind of in-memory mode.
> When set to 'test', the store system will not force sync calls in the 
> following cases  
> - for the log file at each commit
> - for the log file before data page is forced to disk
> - for page allocation when file is grown
> - for data writes during checkpoint
> That means
> - a commit no longer guarantees that the transaction's modification
> will survive a system crash or JVM termination
> - the database may not recover successfully upon restart
> - a near full disk at runtime may cause unexpected errors
> - database can be in an inconsistent state
> This setting is provided for performance reasons and should ideally
> only be used when the system can withstand the above consequences.
> One sample use would be to use this mode (derby.system.durability=test)
> when using Derby as a test database, where high performance is required
> and the data is not very important.   
> If database is booted with derby.system.durability=test, the following warning message
is logged in derby.log
> WARNING: The database is booted with derby.system.durability=test. In this mode, it is
possible that database may not be able to recover, committed transactions may be lost, database
may be in an inconsistent state. Please use this mode only when these consequences are acceptable

> and a similar message will appear in derby.log  if the database was booted with derby.system.durability=test
at any time previously.
> It is important to realize that once the database is booted with derby.system.durability=test,
there are no guarantees on if the database is consistent or not. 
> -------------------
> Valid supported values are test
> Example
> derby.system.durability=test
> One can set this as a command line option to the JVM when starting the
> application or in the derby.properties file. It is a system level 
> property.
> This property is static; if you change it while Derby is running, 
> the change does not take effect until you reboot.  

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