Support database
parameters do not have to be changed for normal operation. Changing them
requires very detailed knowledge of the database system. For more information
about the other database parameters, see General Database
Parameters, Special Database
Parameters and liveCache
Parameters.
Changes to database parameters do not take effect until the database instance is restarted.
Support database parameters
Parameters |
Description |
_BACKUP_HISTFILE |
Name of the history file for data and log backups; contains information about all backups that were previously created |
_BACKUP_MED_DEF |
Name of the file containing the definitions of the backup media |
_EVENTFILE |
Name of the file in which events are logged |
_EVENTFILE |
Size of the file in which events are logged; it is cyclically overwritten |
_IDXFILE_LIST_SIZE |
Number of temporary intermediate result files for parallel indexing Large tables are indexed with the help of several sever tasks. These server tasks write their results in temporary files. When the number of these files reaches the value of this parameter, then the files have to be merged before the actual index can be created. This results in a decline in performance. |
_IOPROCS_PER_DEV |
Number of threads that are available for asynchronous I/O operations (for each data volume and system used) |
_KERNELDIAGFILE |
Name of the log file of the kernel |
_KERNELDUMPFILE |
Name of the dump file that is written by the kernel when the system crashes. The content of the data cache and the converter are saved in this file. Size your system so that sufficient memory space is available for this file (approximately CACHE_SIZE + 10%). Note also parameter DIAG_HIST_NUM. |
_KERNELTRACEFILE |
File in which the kernel writes the trace entries. Trace entries are only written if the database trace was switched on previously. |
_MAXEVENTTASKS |
Maximum number of event tasks |
_MAXTASK_STACK |
Size of the stack that is used by the user tasks |
_MINREPLY_SIZE |
Minimum size of the memory that is available in a packet (shared memory segment) for the reply |
_MULT_IO_BLOCK_CNT |
Block size that is used when writing data from the data cache to the data volumes. The optimum block size depends on the hardware and software that is used. |
_PACKET_SIZE |
Size of the packets (shared memory segments) in which SQL statements and data are transferred; a packet consists of a request part and a reply part. |
_READAHEAD_BLOBS |
Number of pages from which large LONG values are imported in advance by additional server tasks LONG values are often too large to be transferred to the client in a single request packet and are split into several request packets. To increase performance, server tasks can import additional parts of the LONG value while the first request packet are being sent. |
_RESTART_TIME |
Minimum time between two savepoints (in seconds); corresponds to the time that is required for a restart after a system crash. Regardless of this, a savepoint is always written in the following cases: · After an index was created · If the number of pages released by a savepoint is larger than the number of free blocks in the data volumes |
_RTEDUMPFILE |
File in which the kernel writes information about the runtime environment if the system crashes |
_SERVERDB_FOR_SAP |
Specifies whether the database instance is used in an SAP system |
_TASKCLUSTER_01 to _03 |
These parameters describe how the user tasks are distributed to user tasks; do not change these parameters before speaking with support |
_USE_ASYNC_IO |
Specifies whether operating functions or special I/O threads are used for asynchronous I/O operations |
_USE_IOPROCS_ONLY |
Specifies whether I/O operations should be carried out exclusively by special I/O threads, or whether the kernel should decide whether a task executes an I/O operation, or if it passes the I/O operation to a special I/O thread |
ALLOW_DEMANGLE |
Specifies whether C/C++ demangling should be used |
ALLOW_MULTIPLE_SERVERTASK_UKTS |
Specifies whether the server tasks are distributed to the available user kernel threads or if they share a user kernel thread |
EXPAND_COM_TRACE |
Specifies whether storage space is reserved when COM trace files are created |
INIT_ALLOCATORSIZE |
Initial size of the main memory that is reserved at the start of a database session |
LOAD_BALANCING_DIF |
For load balancing; specifies by how much longer the task to be moved had 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) |
LOAD_BALANCING_EQ |
For load balancing; specifies which time difference should still be regarded as equal when comparing waiting tasks (as a percentage) |
MAX_SERVERTASK_STACK |
Maximum size of the stack that is used by the server tasks |
MAX_SPECIALTASK_STACK |
Maximum size of the stack that is used by special tasks (all except user tasks and server tasks) |
MAXVOLUMES |
Maximum number of data and log volumes including mirrored volumes; calculated by the system |
OMS_STREAM_TIMEOUT |
Maximum wait time for all database session that may elapse until the reply to an OMS stream request to a client (in seconds) |
OPTIM_CACHE |
Specifies whether the search strategy is determined only once or each time a parsed SQL statement is executed; for prepared statements with parameters it may be sufficient to determine the search strategy only once |
SET_VOLUME_LOCK |
Specifies whether a lock is set 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: · It is an NFS-mounted volume · It is a hot standby system (HS_STORAGE_DLL is set) |
SHOW_MAX_STACK_USE |
Logs the maximum stack consumption of each task in the kernel log; set this parameter to YES for diagnosis purposes only, as it affects performance during operation |
SUPPRESS_CORE |
Specifies whether kernel core dumps are suppressed |
USE_SYSTEM_PAGE_CACHE |
Specifies whether the database instance uses the system page cache for buffering memory pages that are no longer required |
XP_MP_REGION_LOOP |
Overrides MP_RGN_LOOP |