Support Database Parameters 
The following overview describes database parameters belonging to the SUPPORT group. Most support database parameters are for troubleshooting. In normal operation, it is not necessary to change the support database parameters. Changing support database parameters requires detailed knowledge of the database system.
For information about other database parameters, see
To change the values of database parameters, use one of the following database tools: Database Studio, Database Manager CLI, or CCMS (in SAP systems only). More information:
Database Studio, Changing Database Parameters
Database Administration in CCMS, Parameters
Most changes to database parameters take effect only after the database has been restarted.
However, you can change certain database parameters while the database is running, that is in the ONLINE or ADMIN operational state (see the description of individual database parameters for more information). For these changes you can define when they are to become effective:
Until the next restart
After the next restart
Immediately and permanently
Note
Starting with version 7.7.03 of the database software, the names of many database parameters have changed.
Some database parameters have also been designated obsolete. These parameters have either been removed already or will be removed in one of the next database versions.
More information: Obsolete Database Parameters
Name (from version 7.7.03) |
Old Name (up to and including version 7.7.02) |
Description |
Change Restrictions |
More Information |
|---|---|---|---|---|
CommandBufferSize |
_PACKET_SIZE |
Size of the packages (shared memory segments) in which SQL statements and data are transferred A package consists of a request part and a reply part. The minimum package size is 48 KB. |
Changes only apply after a restart of the database. |
- |
DataIOClusterSize |
DATA_IO_BLOCK_COUNT |
Block size that the database system uses when writing data pages from the data cache to the data area. The optimum block size depends on your hardware and software. |
Changes only apply after a restart of the database. |
- |
DeadlockDumpFileName |
DEADLOCK_DUMP_FILENAME |
Determines whether the system writes a dump file when it encounters an SQL deadlock situation If you do not specify a file name, the system does not write a dump file. If you specify a file name, the system writes a dump file with that name in the database run directory. Note that the dump file can only be analyzed by development support. |
Can be changed in ONLINE or ADMIN operational state |
|
EnableMultipleServerTaskUKT |
ALLOW_MULTIPLE_SERVERTASK_UKTS |
Specifies whether the database system distributes the server tasks to the available user kernel threads. Otherwise they all run in the same user kernel thread. |
Changes only apply after a restart of the database. |
- |
EnableRemoveUndoOnTransactionEnd |
- |
YES: All undo files that are not needed for the history or for the garbage collectors are removed by the transactions themselves. This means that nearly all OLTP undo files will be removed at the end of a transaction. NO: The undo files are removed by the garbage collectors. |
Can be changed in ONLINE and ADMIN operational state |
Concepts of the Database System, Working Memory Areas |
EnableSymbolDemangling |
SYMBOL_DEMANGLING |
Specifies whether the database system carries out C/C++ demangling |
Can be changed in ONLINE and ADMIN operational state |
- |
EnableVariableInput EnableVariableOutput |
USEVARIABLEINPUT |
These parameters determine how the system transfers the content of variables between client and kernel. The system either transfers the actual length of the content or the maximum possible length of the content. In the latter case, the system fills up the content up to the maximum length (depending on the data type). |
Changes only apply after a restart of the database |
- |
EventFileName |
_EVENTFILE |
Name of the file in which the database system logs events |
Changes only apply after a restart of the database. |
|
EventFileSize |
_EVENTSIZE |
Size of the file in which the database system logs events (in KB) |
Changes only apply after a restart of the database. |
- |
FloatingServiceTasks |
- |
Maximal number of tasks in the floating service task pool The floating service task pool contains tasks that the system can use for events and for Database Analyzer You must configure at least 2 event tasks and 1 Database Analyzer task. See also PreservedEventTasks and PreservedDBAnalyzerTasks |
Changes only apply after a restart of the database. |
Concepts of the Database Systems, Tasks |
InitialAllocatorSize |
INIT_ALLOCATORSIZE |
Initial size of the working memory that is reserved at the start of a database session |
Changes only apply after a restart of the database. |
- |
KernelDumpFileName |
_KERNELDUMPFILE |
Name and location of the dump file that is written by the kernel when the database crashes The system writes the contents of the data cache and the converter to this file. Caution: This file may become very large. You can estimate the size of this file in the following way: CacheMemorySize + 10%. |
Changes only apply after a restart of the database. |
Parameter DIAG_HIST_NUM |
KernelTraceFile |
_KERNELTRACEFILE |
Name and location of th file to which the kernel writes the database trace messages The kernel only writes database trace messages if you previously activated the database trace. |
Changes only apply after a restart of the database. |
Concepts of the Database System, Load Balancing Between User Kernel Threads |
LoadBalancingWorkloadDeviation |
LOAD_BALANCING_EQ |
For internal load balancing Specifies which time delays the system should regard as equal when comparing waiting tasks (as a percentage) |
Can be changed in ONLINE and ADMIN operational state |
- |
LoadBalancingWorkloadThreshold |
LOAD_BALANCING_DIF |
For internal load balancing If the system considers moving a task from one user kernel thread to another, this parameter specifies the amount of time this task has to have waited longer than the longest waiting task in the target user kernel thread (as a percentage). |
Can be changed in ONLINE and ADMIN operational state |
- |
LogIOClusterSize |
LOG_IO_BLOCK_COUNT |
Block size that the database system uses when writing log pages from the log queues to the log area The optimum block size depends on your hardware and software. |
Changes only apply after a restart of the database. |
- |
MaxPagerTasks |
MAXPAGER |
Maximum number of pagers The system calculates this parameter from the MAXDATAVOLUMES parameter and other parameters. |
Not changeable You can override this parameter using the XP_MAXPAGER parameter. |
- |
MaxSavepointTimeInterval |
_RESTART_TIME |
Minimum time between two savepoints (in s) This corresponds to the time that is required for a restart after a system crash. Note that the database system always writes a savepoint in the following cases:
|
Changes only apply after a restart of the database. |
- |
MaxServerTaskStackSize |
MAX_SERVERTASK_STACK |
Maximum size of the stack that is used by the server tasks |
Changes only apply after a restart of the database. |
|
MaxSpecialTaskStackSize |
MAX_SPECIALTASK_STACK |
Maximum size of the stack that is used by the special tasks (all tasks except user tasks and server tasks) |
Changes only apply after a restart of the database. |
- |
MaxTaskStackSize |
_MAXTASK_STACK |
Size of the stack that is used by the user tasks |
Changes only apply after a restart of the database. |
|
MaxTempFilesPerIndexCreation |
_IDXFILE_LIST_SIZE |
Number of temporary result files when the system is creating an index using multiple server tasks (parallel indexing) The database system indexes large tables using multiple server tasks. These server tasks write their results to temporary files. When the number of these files reaches the value of this parameter, the database system has to merge the files before it can generate the actual index. This results in a decline in performance. |
Can be changed in ONLINE and ADMIN operational state |
- |
OMSStreamTimeout |
OMS_STREAM_TIMEOUT |
Maximum wait time for all database sessions that may elapse until the reply to an OMS stream request from a client (in s) |
Can be changed in ONLINE and ADMIN operational state |
- |
PreservedDBAnalyzerTasks |
- |
Minimum number of Database Analyzer tasks in the floating service task pool See also FloatingServiceTasks |
Changes only apply after a restart of the database. |
Database Analyzer documentation |
PreservedEventTasks |
_MAXEVENTTASKS |
Minimum number of event tasks in the floating service task pool See also FloatingServiceTasks The database system uses event tasks both for Event Dispatcher commands and for the DBM commands event_wait,event_receive, event_available, auto_extend and auto_update_statistics. |
Changes only apply after a restart of the database. |
Glossary, Event |
QueryAnalysisMode |
- |
Specifies which internal mechanism is used for semantic analysis of queries. To enable extended semantic analysis and as a prerequisite for the QueryRewrite function, choose EXTENDED. |
Can be changed in ONLINE and ADMIN operational state |
Special database parameter EnableQueryRewrite |
ReadAheadLobThreshold |
_READAHEAD_BLOBS |
If a LOB value is too large to be transferred to the client in a single request package, the database system splits it into several request packages. To increase performance, server tasks can import further parts of the LOB value while the first request package is being sent. This parameter specifies the minimum number of pages for a LOB value to be imported in advance by additional server tasks. |
Can be changed in ONLINE and ADMIN operational state |
- |
RTEDumpFileName |
_RTEDUMPFILE |
Name of the file to which the kernel writes information about the runtime environment if the system crashes |
Changes only apply after a restart of the database. |
- |
ShowMaxStackUsage |
SHOW_MAX_STACK_USE |
Specifies whether the system logs the maximum stack usage of each task in the kernel log Only set this parameter to YES for diagnosis purposes as it compromises performance. |
Changes only apply after a restart of the database. |
- |
TaskCluster01 to TaskCluster03 |
_TASKCLUSTER_01 to _03 |
These parameters determine how the database system distributes user tasks to the threads. Only change these parameters after consulting support. |
Changes only apply after a restart of the database. |
- |
TaskSpecificCatalogCacheMinSize |
CAT_CACHE_MINSIZE |
Minimum size of the task-specific catalog cache (in bytes) |
Changes only apply after a restart of the database. |
Concepts of the Database System, Working Memory Areas |
UpdateStatParallelServerTask |
UPDATESTAT_PARALLEL_SERVERS |
Specifies how many parallel server tasks the database system uses for updating the SQL optimizer statistics |
Can be changed in ONLINE and ADMIN operational state |
- |
UseAsynchronousIO |
_USE_ASYNC_IO |
Specifies whether operating system functions or special I/O threads are used for asynchronous I/O operations |
Changes only apply after a restart of the database. |
- |
UseColumnCompression |
COLUMNCOMPRESSION |
Only for columns that are not primary key columns Specifies whether the system can store the column values in variable length or not Default value: YES (columns have variable length, so the values can be compressed if necessary) |
Can be changed in ONLINE and ADMIN operational state |
- |
UseExtendedOracleSQLMode |
_SERVERDB_FOR_SAP |
Specifies whether the database is being used in an SAP system |
Can be changed in ONLINE and ADMIN operational state |
- |
UseFilesystemCacheForBackup |
- |
Specifies whether the database system uses the operating system's file system cache for I/O operations (O_DIRECT flag) when opening volumes or data carriers for backup or restore YES: The database system does not use the O_DIRECT flag NO: The database system uses the O_DIRECT flag (if this flag is supported by the file system; note that this flag is ignored for Linux kernels < 2.4.18). |
Changes only apply after a restart of the database. |
- |
UseFilesystemCacheForVolume |
(USE_OPEN_DIRECT)
This parameter replaces the USE_OPEN_DIRECT parameter, but with a different logic. For backward compatibility, DeprecatedParameter29 has been introduced as a direct replacement for USE_OPEN_DIRECT, see Obsolete Database Parameters. After migrating from an earlier database version and if USE_OPEN_DIRECT was set explicitly for example using a script, the system changes UseFilesystemCacheForVolume to the opposite value. Note though that after you have changed UseFilesystemCacheForVolume for the first time, it does not depend on USE_OPEN_DIRECT any longer. End of the caution. |
Specifies whether the database system uses the operating system's file system cache for I/O operations O_DIRECT flag) when it is opening volumes for normal database operation YES: The database system does not use the O_DIRECT flag NO: The database system uses the O_DIRECT flag (if this flag is supported by the file system; note that this flag is ignored for Linux kernels < 2.4.18). |
Changes only apply after a restart of the database. |
- |
UseStrategyCache |
OPTIM_CACHE |
Specifies whether the database system determines the search strategy only once or every time it executes a parsed SQL statement For prepared statements with parameters, it may be sufficient to determine the search strategy only once. |
Can be changed in ONLINE and ADMIN operational state |
- |
UseSystemPageCache |
USE_SYSTEM_PAGE_CACHE |
Specifies whether the database uses the system page cache for buffering memory pages that are no longer required |
Changes only apply after a restart of the database. |
- |
UseSystemTrigger |
ENABLE_SYSTEM_TRIGGERS |
Specifies whether system triggers are called when the database is restarted |
Changes only apply after a restart of the database. |
- |
UseVolumeLock |
SET_VOLUME_LOCK |
Specifies whether the database system sets a lock when a volume is added, which prevents the same volume from being added again later In the following cases, it may make sense to set this parameter to NO:
|
Changes only apply after a restart of the database. |
- |
Caution