13.9. LOB Considerations

LOBs and XML documents are streamed from the JBoss Data Virtualization server to the JDBC API. Normally, these values are not materialized in the server memory, avoiding potential out-of-memory issues. When using style sheets, or XQuery, whole XML documents must be materialized on the server. Even when using the XMLQuery or XMLTable functions and document projection is applied, memory issues may occur for large documents.

LOBs are broken into pieces when being created and streamed. The maximum size of each piece when fetched by the client can be configured with the lob-chunk-size-in-kb property.

The default value is 100. When dealing with extremely large LOBs, you may consider increasing lob-chunk-size-in-kb to decrease the amount of round-trips to stream the result. Setting the value too high may cause the server or client to have memory issues.

Source LOB values are typically accessed by reference, rather than having the value copied to a temporary location. Thus care must be taken to ensure that source LOBs are returned in a memory-safe manner. This caution is more for the source driver vendors not to consume VM memory for LOBs.