Support Database Parameters 
The following overview describes database parameters belonging to the Support Database Parameters 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 Manager CLI Tutorial, Changing the Values of 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 individual 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
If you change a database parameter whose value is normally calculated by the system, then the system will consider this user-defined value for all subsequent recalculations of database parameter values. The system discards and recalculates this user-defined value only if it is not within the permitted value range (for example, after the database software has been updated).
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 |
- |
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 |
- |
EnableSymbolDemangling |
SYMBOL_DEMANGLING |
Specifies whether the database system performs C/C++ demangling |
Can be changed in ONLINE and ADMIN operational state |
- |
EnableSynchronousTaskIO |
_USE_IOPROCS_ONLY |
YES: I/O operations are executed only by special I/O threads NO: The kernel decides whether a task is to execute an I/O operation itself or delegate the I/O operation to a special I/O thread |
Can be changed in ONLINE and ADMIN operational state |
- |
EnableVariableInput EnableVariableOutput |
USEVARIABLEINPUT |
Specifies whether the current length of the variable contents or the maximum length of these variables is transmitted between client and kernel. In the latter case, the maximum length may be used depending on the data type of the variables. |
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 of the dump file that is written by the kernel when the system crashes To this file, the database system writes the contents of the data cache and the converter. Size your system so that sufficient memory space is available for this file (approximately CACHE_SIZE + 10%). |
Changes only apply after a restart of the database |
Parameter DIAG_HIST_NUM |
KernelTraceFile |
_KERNELTRACEFILE |
File to which the kernel writes trace entries The kernel only writes trace entries 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 load balancing Specifies which time delay should be regarded as equal when comparing waiting tasks (as a percentage) |
Changes only apply after a restart of the database |
- |
LoadBalancingWorkloadThreshold |
LOAD_BALANCING_DIF |
For load balancing Specifies by how much longer the task to be moved has to wait in its user kernel thread than the task that has been waiting the longest in the target user kernel thread (as a percentage) |
Changes only apply after a restart of the database |
- |
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 |
- |
PreservedDBAnalyzerTasks |
- |
Minimal 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 |
Minimal number of event tasks in the floating service task pool See also FloatingServiceTasks The database system uses event tasks both for Event Dispatcher 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 |
Database Manager CLI, |
MaxPagerTasks |
MAXPAGER |
Maximum number of pagers; calculated by the database system from MAXDATAVOLUMES and other parameters |
Not changeable You can override this parameter with XP_MAXPAGER. |
- |
MaxSavepointTimeInterval |
_RESTART_TIME |
Minimum time between two savepoints (in s); corresponds to the time that is required for a restart after a system crash Furthermore, 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 special tasks (all 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 in the case of 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 |
- |
MaxVolumes |
MAXVOLUMES |
Maximum number of data and log volumes including mirrored volumes |
Changes only apply after a restart of the database |
- |
MiniDumpType |
MINI_DUMP |
Defines whether the system writes the memory dumps knlmini.dmp and srvmini.dmp (for postmortem debugging) and how much information these dumps contain |
Changes only apply after a restart of the database |
- |
OMSStreamTimeout |
OMS_STREAM_TIMEOUT |
Maximum wait time for all database sessions that may elapse until the reply to an OMS stream request to a client (in s) |
Can be changed in ONLINE and ADMIN operational state |
- |
ReadAheadLobThreshold |
_READAHEAD_BLOBS |
Number of pages from which large LOB values are imported in advance by additional server tasks 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. |
Can be changed in ONLINE and ADMIN operational state |
- |
ReservedCommandBufferReplySize |
_MINREPLY_SIZE |
Minimum size of the memory that is available in a package (shared memory segment) for the reply 0: The whole package is available for the request/reply. |
Changes only apply after a restart of the database |
- |
RTEDumpFileName |
_RTEDUMPFILE |
File 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 |
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 describe 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 |
Specifies whether the column values can be stored in variable length or not. Default value: YES (columns have variable length, so the values can be compressed if necessary) Only for columns that are not primary key columns |
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 recovery 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 |
- |
UseSystemTriggers |
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