OpenEdge Data Management: DataServer for Microsoft SQL Server

Initial Programming Considerations
Data source record locking
2–36
In a DataServer application, MS SQL Server handles all of its own locking issues. ABL locking
rules are modified when you access information from a MS SQL Server data source. As a result,
the OpenEdge phrases NO–LOCK and SHARE–LOCK have isolation-level dependencies. The
EXCLUSIVE-LOCK behaves the same in MS SQL Server as in an OpenEdge database.
Table 2–13 provides data source specific comparisons.
Table 2–13: OpenEdge database and data source locking
OpenEdge Data source
NO–LOCK Supports the NO–LOCK option in a manner consistent with the
OpenEdge database when transaction isolation level is set to read
uncommitted.
SHARE–LOCK Supports shared locks at the table, page, and record level.
However, the scope and duration of the OpenEdge database vs.
MS SQL Server shared locks can differ depending on how data
source cursors behave at a transaction boundary and how isolation
levels are set. The repeatable read isolation level emulates the
OpenEdge database SHARE-LOCK behavior most closely. For more
information, see your MS SQL Server documentation.
EXCLUSIVE–LOCK Supports the EXCLUSIVE-LOCK option in a manner consistent with
the OpenEdge database using any available isolation level.
However, the MS SQL Server optimizer might produce locks at
either the table, page, or the record level.
The DataDirect drivers provide four transaction isolation levels in the following order from least
to most restrictive: read uncommitted, read committed, repeatable read, and serializable. In a
multi-user configuration, you can isolate users from each other in your data source by setting
the isolation level. In your OpenEdge schema holder, use the –Dsrv TXN_ISOLATION,n
connection parameter (where n = 1, 2, 4, or 8) to set the isolation level in ODBC. See Microsoft
documentation and the MS SQL Server documentation for more information.
Note: MS SQL Server might use page-level or table-level locking rather than record-level
locking, if its optimizer determines this is the best choice. This can affect data access
when two or more users attempt to read or update different records that are on the same
page. See your MS SQL Server documentation for details.
Table 2–14 shows the possible –Dsrv TXN_ISOLATION,n values with the respective meaning.
Table 2–14: TXN_ISOLATION values in the –Dsrv parameter
Value Meaning
1 Read uncommitted (default)
2 Read committed
4 Repeatable read
8 Serializable