OpenEdge Data Management: DataServer for Microsoft SQL Server

Chapter 8: Troubleshooting
ODBC_DEF_BLKCACHESZ is the default value for QT_CACHE_SIZE when block cursors are
enabled. This value is currently set to 10,000 bytes.
ODBC_DEF_LHDCACHESZ is the default value of QT_CACHE_SIZE when lookahead cursors
are enabled. It is currently set at 30,000 bytes.
The value of QT_CACHE_SIZE represents an upper limit for the row space available to
the lookahead cache, not the amount of space a lookahead cache will actually use.
This highlights a key distinction between block and lookahead cursors. The “cache
size” for block cursors is preallocated before results are retrieved so this value
represents an actual allocated amount. For lookahead cursors, memory is accrued as
rows are read back from the result set and added to the cache. So the “cache size”
specifies an upper limit on the number of cached rows allowable, not an exact amount
of space that will be allocated as is the case with block cursors.
Adjusting values
With the default size, approximately 6.5 open cursors and result sets per table can be
established at a given time before the maximum block memory area
(PRGRS_TABLE_BLOCKSIZE) is exceeded. At 10,000 bytes, 104 new block allocations
can be established before the maximum block memory (PRGRS_MAX_MBLOCKSIZE) is
exceeded. If record sizes are large or the typical row counts for your results sets are
large, you can consider increasing one or both of these sizes. Conversely, if record
sizes are small or the typical row counts for your results are small, you can consider
decreasing theses sizes. Consider setting these tuning parameters based on your
typical requirements and then override them for specific queries that are the exceptions
using the query tuning option.
ODBC driver problems
The ODBC drivers use the Microsoft Windows DLL technology. A driver problem can
leave the driver’s DLL in an unstable state. In this case, the next attempt to connect to
the driver might fail with a GPF or with an unexpected error message. If this occurs,
you might need to unload the driver’s DLL by using Windows utilities or by restarting
Windows.
In addition, drivers utilized by ODBC can get overlaid with incompatible DLL versions
as other products are installed on your system. You might need to reinstall ODBC
drivers and products if such incompatibilities occur.
332 OpenEdge Data Management: DataServer for Microsoft SQL Server