Configuring write-behind loader support

ObjectGrid descriptor XML file

<objectGrid name="library" >
     <backingMap name="book" writeBehind="T300;C900" pluginCollectionRef="bookPlugins"/>

In the previous example, write-behind support of the book backing map is enabled with parameter T300;C900. The write-behind attribute specifies the maximum update time, maximum key update count, or both. The format of the write-behind parameter is:

write-behind attribute::= <defaults> | <update time> [ ";" <conversion clause> ]| <update key count> 
[ ";" <conversion clause> ]| <conversion clause> | <update time> ";" <update key count> [ ";" <conversion clause> ]

If you want the write-behind loader to convert insert and update operations to an upsert, you can set the configuration option ConvertToUpsert=<true|false> on the write-behind attribute <conversion clause>. By setting this configuration option to true, the operations are converted to an upsert before it is passed to the loader. Before you set ConvertToUpsert=true, you should check the specifications of back-end loader to ensure that upsert operations are supported. The default value is false.

update time ::= "T" <positive integer>
update key count ::= "C" <positive integer>
defaults ::= "" {table}
conversion clause ::= ConvertToUpsert=<true|false> 

These parameters are only hints. The real update count and update time will be within close range of the parameters. However, we do not guarantee that the actual update count or update time are the same as defined in the parameters. Also, to prevent all partitions from accessing the database simultaneously, the ObjectGrid randomizes the update starting time. For example, the first update can occur after up to twice as long as the real update time.

In the previous example T300;C900, the loader writes the data to the back-end when 300 seconds have passed since the last update or when 900 keys are pending to be updated. The default update time is 300 seconds and the default update key count is 1000.

Table 1. Some write-behind options. For an attribute value, the table lists the update time and the update key count.

Attribute	Time
T100	The update time is 100 seconds, and the update key count is 1000 (the default value).
C2000	The update time is 300 seconds (the default value), and the update key count is 2000.
T300;C900	The update time is 300 seconds and the update key count is 900. The loader receives upsert LogElement operations instead of insert and update operations.
""	The update time is 300 second (the default value), and the update key count is 1000 (the default value). Note: If you configure the write-behind loader as an empty string: writeBehind="", the write-behind loader is enabled with the default values. Therefore, do not specify the writeBehind attribute if you do not want write-behind support enabled.

Programmatically enabling write-behind support

When you are creating a backing map programmatically for a local, in-memory eXtreme Scale, you can use the following method on the BackingMap interface to enable and disable write-behind support.

public void setWriteBehind(String writeBehindParam);

For more details about how to use the setWriteBehind method, see BackingMap interface.