existing connections to that member terminate. However, when new type 2
connections to the data sharing group are requested, DB2 for z/OS connects the
application to an alternative member of the data sharing group that is active on the
same LPAR.
Related reference
“ IBM Data Server Driver for JDBC and SQLJ properties for DB2 for z/OS” on
page 228
Memory use for IBM Data Server Driver for IBM Data Server Driver for
JDBC and SQLJ type 2 connectivity on DB2 for z/OS
In general, applications that use IBM Data Server Driver for JDBC and SQLJ type 2
connectivity require more memory than applications that use IBM Data Server
Driver for JDBC and SQLJ type 4 connectivity.
With IBM Data Server Driver for JDBC and SQLJ type 4 connectivity, an
application receives data from the DB2 database server in network packets, and
receives only the data that is contained in a particular row and column of a table.
Applications that run under IBM Data Server Driver for JDBC and SQLJ type 2
connectivity on DB2 for z/OS generally require more memory. IBM Data Server
Driver for JDBC and SQLJ type 2 connectivity has a direct, native interface to DB2
for z/OS. For IBM Data Server Driver for JDBC and SQLJ type 2 connectivity, the
driver must provide memory in which DB2 for z/OS writes data. Because the
amount of data that is needed can vary from row to row, and the driver has no
information about how much memory is needed for each row, the driver must
allocate the maximum amount of memory that any row might need. This value is
determined from DESCRIBE information on the SELECT statement that generates
the result table. For example, when an application that uses IBM Data Server
Driver for JDBC and SQLJ type 2 connectivity selects a column that is defined as
VARCHAR(32000), the driver must allocate 32000 bytes for each row of the result
table.
The extra memory requirements can be particularly great for retrieval of LOB
columns, which can be defined with lengths of up to 2 GB, or for CAST
expressions that cast values to LOB types with large length attributes. Even when
you use a 64-bit JVM, all native connectivity to DB2 for z/OS is below the bar,
with 32-bit addressing limits. Although the maximum size of any row is defined as
approximately 2 GB, the practical maximum amount of available memory for use
by IBM Data Server Driver for JDBC and SQLJ type 2 connectivity is generally
significantly less. Therefore, applications that run under IBM Data Server Driver
for JDBC and SQLJ type 2 connectivity and involve LOBs with large length
attributes can fail with out-of-memory errors.
Two ways to alleviate excess memory use for LOB retrieval and manipulation are
to use progressive streaming or LOB locators. You enable progressive streaming or
LOB locator use by setting the progressiveStreaming property or the
fullyMaterializeLobData property.
Related concepts
“LOBs in JDBC applications with the IBM Data Server Driver for JDBC and
SQLJ” on page 49
Related reference
“Properties for the IBM Data Server Driver for JDBC and SQLJ” on page 201
98 Application Programming Guide and Reference for Java
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