The following
overview describes the special database parameters. For more information about
other database parameters, see General Database
Parameters, Support Database
Parameters and liveCache
Parameters.
Changes to database parameters do not take effect until the database instance is restarted.
Special database parameters (extended)
Parameters |
Description |
_COMMENT |
Description of the database instance |
_DATA_CACHE_RGNS |
Number of critical sections into which the data cache is divided. This division enables parallel writing to the data cache. This parameter is calculated by the database system and cannot be changed. You can override the parameter for test purposes, however, using the XP_DATA_CACHE_RGNS support database parameter. |
_EVENT_ALIVE_CYCLE |
Time interval in which the kernel creates an event that shows it is still running (prevents network timeout) |
_MAXEVENTS |
Maximum number of events held in the main memory by the kernel for processing by the Database Manager |
_MAX_MESSAGE_FILES |
Maximum number of trace files that can be opened in parallel |
_ROW_RGNS |
Number of critical sections into which the total of all rows is divided in the lock list. This division enables parallel access to the lock list. |
_TAB_RGNS |
Number of critical sections into which the total of all tables is divided in the lock list. This division enables parallel access to the lock list. |
_TRANS_RGNS |
Number of critical sections into which the total of all transactions is divided in the lock list. This division enables parallel access to the lock list. |
_UNICODE |
Determines whether the database system uses UNICODE as the character string. You define this database parameter when you create the database instance; it cannot be changed later. |
AUTO_RECREATE_BAD_INDICES |
Indices marked as BAD are recreated automatically after a restore |
BACKUP_BLOCK_CNT |
Block size for describing backup media; only applicable for tapes that have an optimal block size. |
CAT_CACHE_SUPPLY |
Memory size of the catalog cache for all user tasks (in pages) |
CONVERTER_REGIONS |
Number of critical sections into which the converter is divided. This division enables parallel writing to the converter. |
DATE_TIME_FORMAT |
System default for the date and time format. Each user can change the date and time format for a session by making corresponding entries in the database tool (such as in the Loader using standard_date_mask) or by making corresponding entries in SQL statements (datetimeformat). See Date and Time Format. |
DEADLOCK_DETECTION |
Maximum search depth for deadlock detection; deadlocks that were not detected up to the specified search depth are only resolved by a timeout (see REQUEST_TIMEOUT) |
DEFAULT_CODE |
System default for the code attribute. Applies only to the column values of the data type CHAR[ACTER], VARCHAR and LONG[VARCHAR]. |
DIAG_HISTORY_NUM |
Number of histories in the <diag_history_path> directory |
DIAG_HISTORY_PATH |
Directory <diag_history_path> for the histories of log files |
FORMATTING_MODE |
The database system formats the volumes when the database instance is created. Define the type of formatting with this parameter. A parallel formatting is only useful for data volumes of type File, which are located on different hard disks. |
FORMAT_DATAVOLUME |
Suppresses the formatting of data volumes when a new database instance is created; only useful for test purposes |
HIRES_TIMER_TYPE |
Type of time measurement that is used by the kernel for internal operations; only useful for multiprocessor computers where there can be synchronization problems between the CPUs |
HS_DELAY_TIME_<NNN> |
Only for hot standby systems; time delay in seconds with which the standby component NNN redoes changes of the master component. |
HS_NODE_<NNN> |
Computer name / address of the hot standby component NNN. The default value for the master component is HSS_NODE_001. |
HS_STORAGE_DLL |
Only for hot standby systems; name of the library with which the storage management system is controlled. The default value is libhsscopy. |
HS_SYNC_INTERVAL |
Only for hot standby systems; minimum time delay between two commands of the master component to synchronize the standby components, specified in seconds. |
JOIN_MAXTAB_LEVEL4 |
Parameter of the SQL Optimizer; see JOIN_SEARCH_LEVEL |
JOIN_MAXTAB_LEVEL9 |
Parameter of the SQL Optimizer; see JOIN_SEARCH_LEVEL |
JOIN_OPERATOR_IMPLEMENTATION |
Specifies whether the SQL Optimizer uses the operator graph for joins. |
JOIN_SEARCH_LEVEL |
Algorithm used by the SQL Optimizer for the join sequence search; see Database Parameter JOIN_SEARCH_LEVEL |
JOIN_TABLEBUFFER |
Size of the buffer that the SQL Optimizer can use for each join step for a read operation. |
KERNELDIAGSIZE |
Size of log file knldiag (in KB) |
LOAD_BALANCING_CHK |
Time interval in which the database system checks whether load balancing should be useful (in s) |
LOG_BACKUP_TO_PIPE |
Specifies whether a log backup to pipes is allowed |
LOG_IO_QUEUE |
Size of the log queue (in pages) |
LRU_FOR_SCAN |
Specifies whether the total data cache is used for scans |
MAXRGN_REQUEST |
Maximum number of attempts by a task to access a critical section. If this number is exceeded, the task allows a different task of the same user kernel thread to access the CPU. |
MAXSERVERTASKS |
Number of server tasks |
MAX_RETENTION_TIME |
liveCache parameter |
MEMORY_ALLOCATION_LIMIT |
Maximum memory to be used by the database instance (in KB) |
MEM_ENHANCE_LIMIT |
Maximum additional memory to be used, through a Memory Scalability Enhancement for example (in MB) |
MIN_RETENTION_TIME |
liveCache parameter |
MP_RGN_LOOP |
Maximum number of attempts by a task to access a critical section that is locked by a different task; if this number is exceeded, the accessing task changes its state to "waiting". |
OFFICIAL_NODE |
Only for cluster systems; official name of the database within the cluster system. Defined by the system administrator. |
OPTIM_INV_ONLY |
Defines whether the SQL Optimizer should use the index-only strategy for joins |
OPTIM_MAX_MERGE |
Influences the decision whether the SQL Optimizer uses an index merge strategy; if the number of pages of an index to be merged exceeds the value of OPTIM_MAX_MERGE, then this index is not used for an index-merge strategy. |
REQUEST_TIMEOUT |
Maximum wait time for a lock to be released (in s); for all database sessions, restricts waiting for a lock to be released by another user. If a lock request cannot be fulfilled in the time defined here, a message is sent to the waiting database session. The changes that may have been made within the transaction earlier are rolled back. |
SEQUENCE_CACHE |
Size of the sequence cache (in pages) |
SESSION_TIMEOUT |
Timeout value for database sessions (in s) |
SHAREDSQL |
Activates Shared SQL |
SHAREDSQL_COMMANDCACHESIZE |
Maximum size of the Shared SQL cache (in KB) |
SHAREDSQL_EXPECTEDSTATEMENTCOUNT |
Expected number of SQL statements that are to be saved in the shared SQL cache |
TRACE_PAGES_<task> |
Maximum number of pages that are available to the individual task types for each user kernel thread. Each user kernel thread has its own trace area in the main memory. <task> can have the following values: BUP (Backup Task, not yet implemented), EV (Event Task), GC (Garbage Collector), LW (Log Writer), PG (Pager), SV (Server Task), TI (Timer Task), US (User Task), UT (Utility Task) |
USE_MEM_ENHANCE |
Only for Microsoft Windows; activates Memory Scalability Enhancements for using the memory area beyond the 4 GB limit (such as AWE) |
UTILITY_PROTSIZE |
Size of the log file dbm.utl (in pages) |
VOLUMENO_BIT_COUNT |
Number of bits in the converter block address that is reserved for the logical volume number of a data volume. Permitted values: 6 = VOLUMENO_BIT_COUNT = 12 (see Technical Restrictions) We recommend that you do not change the value that was selected when the database instance was created. If you change the database parameter when the database is running, you then have to restore the database instance to update the data volume numbering. |
XP_DATA_CACHE_RGNS |
Overrides the _DATA_CACHE_RGNS parameter |