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Function documentation Support Database Parameters Locate the document in its SAP Library structure

Use

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 Structure linkliveCache Parameters.

Caution

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

 

 

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