JET_param enumeration
ESENT system parameters.
Namespace: Microsoft.Isam.Esent.Interop
Assembly: Microsoft.Isam.Esent.Interop (in Microsoft.Isam.Esent.Interop.dll)
Syntax
'Declaration
Public Enumeration JET_param
'Usage
Dim instance As JET_param
public enum JET_param
Members
| Member name | Description |
|---|---|
| SystemPath | This parameter indicates the relative or absolute file system path of the folder that will contain the checkpoint file for the instance. The path must be terminated with a backslash character, which indicates that the target path is a folder. |
| TempPath | This parameter indicates the relative or absolute file system path of the folder or file that will contain the temporary database for the instance. If the path is to a folder that will contain the temporary database then it must be terminated with a backslash character. |
| LogFilePath | This parameter indicates the relative or absolute file system path of the folder that will contain the transaction logs for the instance. The path must be terminated with a backslash character, which indicates that the target path is a folder. |
| BaseName | This parameter sets the three letter prefix used for many of the files used by the database engine. For example, the checkpoint file is called EDB.CHK by default because EDB is the default base name. |
| EventSource | This parameter supplies an application specific string that will be added to any event log messages that are emitted by the database engine. This allows easy correlation of event log messages with the source application. By default the host application executable name will be used. |
| MaxSessions | This parameter reserves the requested number of session resources for use by an instance. A session resource directly corresponds to a JET_SESID data type. This setting will affect how many sessions can be used at the same time. |
| MaxOpenTables | This parameter reserves the requested number of B+ Tree resources for use by an instance. This setting will affect how many tables can be used at the same time. |
| MaxCursors | This parameter reserves the requested number of cursor resources for use by an instance. A cursor resource directly corresponds to a JET_TABLEID data type. This setting will affect how many cursors can be used at the same time. A cursor resource cannot be shared by different sessions so this parameter must be set to a large enough value so that each session can use as many cursors as are required. |
| MaxVerPages | This parameter reserves the requested number of version store pages for use by an instance. |
| MaxTemporaryTables | This parameter reserves the requested number of temporary table resources for use by an instance. This setting will affect how many temporary tables can be used at the same time. If this system parameter is set to zero then no temporary database will be created and any activity that requires use of the temporary database will fail. This setting can be useful to avoid the I/O required to create the temporary database if it is known that it will not be used. The use of a temporary table also requires a cursor resource. |
| LogFileSize | This parameter will configure the size of the transaction log files. Each transaction log file is a fixed size. The size is equal to the setting of this system parameter in units of 1024 bytes. |
| LogBuffers | This parameter will configure the amount of memory used to cache log records before they are written to the transaction log file. The unit for this parameter is the sector size of the volume that holds the transaction log files. The sector size is almost always 512 bytes, so it is safe to assume that size for the unit. This parameter has an impact on performance. When the database engine is under heavy update load, this buffer can become full very rapidly. A larger cache size for the transaction log file is critical for good update performance under such a high load condition. The default is known to be too small for this case. Do not set this parameter to a number of buffers that is larger (in bytes) than half the size of a transaction log file. |
| CircularLog | This parameter configures how transaction log files are managed by the database engine. When circular logging is off, all transaction log files that are generated are retained on disk until they are no longer needed because a full backup of the database has been performed. When circular logging is on, only transaction log files that are younger than the current checkpoint are retained on disk. The benefit of this mode is that backups are not required to retire old transaction log files. |
| DbExtensionSize | This parameter controls the amount of space that is added to a database file each time it needs to grow to accommodate more data. The size is in database pages. |
| PageTempDBMin | This parameter controls the initial size of the temporary database. The size is in database pages. A size of zero indicates that the default size of an ordinary database should be used. It is often desirable for small applications to configure the temporary database to be as small as possible. Setting this parameter to SystemParameters.PageTempDBSmallest will achieve the smallest temporary database possible. |
| CacheSizeMax | This parameter configures the maximum size of the database page cache. The size is in database pages. If this parameter is left to its default value, then the maximum size of the cache will be set to the size of physical memory when JetInit is called. |
| CheckpointDepthMax | This parameter controls how aggressively database pages are flushed from the database page cache to minimize the amount of time it will take to recover from a crash. The parameter is a threshold in bytes for about how many transaction log files will need to be replayed after a crash. If circular logging is enabled using JET_param.CircularLog then this parameter will also control the approximate amount of transaction log files that will be retained on disk. |
| OutstandingIOMax | This parameter controls how many database file I/Os can be queued per-disk in the host operating system at one time. A larger value for this parameter can significantly help the performance of a large database application. |
| StartFlushThreshold | This parameter controls when the database page cache begins evicting pages from the cache to make room for pages that are not cached. When the number of page buffers in the cache drops below this threshold then a background process will be started to replenish that pool of available buffers. This threshold is always relative to the maximum cache size as set by JET_paramCacheSizeMax. This threshold must also always be less than the stop threshold as set by JET_paramStopFlushThreshold. The distance height of the start threshold will determine the response time that the database page cache must have to produce available buffers before the application needs them. A high start threshold will give the background process more time to react. However, a high start threshold implies a higher stop threshold and that will reduce the effective size of the database page cache for modified pages (Windows 2000) or for all pages (Windows XP and later). |
| StopFlushThreshold | This parameter controls when the database page cache ends evicting pages from the cache to make room for pages that are not cached. When the number of page buffers in the cache rises above this threshold then the background process that was started to replenish that pool of available buffers is stopped. This threshold is always relative to the maximum cache size as set by JET_paramCacheSizeMax. This threshold must also always be greater than the start threshold as set by JET_paramStartFlushThreshold. The distance between the start threshold and the stop threshold affects the efficiency with which database pages are flushed by the background process. A larger gap will make it more likely that writes to neighboring pages may be combined. However, a high stop threshold will reduce the effective size of the database page cache for modified pages (Windows 2000) or for all pages (Windows XP and later). |
| Recovery | This parameter is the master switch that controls crash recovery for an instance. If this parameter is set to "On" then ARIES style recovery will be used to bring all databases in the instance to a consistent state in the event of a process or machine crash. If this parameter is set to "Off" then all databases in the instance will be managed without the benefit of crash recovery. That is to say, that if the instance is not shut down cleanly using JetTerm prior to the process exiting or machine shutdown then the contents of all databases in that instance will be corrupted. |
| EnableOnlineDefrag | This parameter controls the behavior of online defragmentation when initiated using JetDefragment(JET_SESID, JET_DBID, String, Int32, Int32, DefragGrbit) and JetDefragment2(JET_SESID, JET_DBID, String, Int32, Int32, JET_CALLBACK, DefragGrbit). |
| CacheSize | This parameter can be used to control the size of the database page cache at run time. Ordinarily, the cache will automatically tune its size as a function of database and machine activity levels. If the application sets this parameter to zero, then the cache will tune its own size in this manner. However, if the application sets this parameter to a non-zero value then the cache will adjust itself to that target size. |
| EnableIndexChecking | When this parameter is true, every database is checked at JetAttachDatabase time for indexes over Unicode key columns that were built using an older version of the NLS library in the operating system. This must be done because the database engine persists the sort keys generated by LCMapStringW and the value of these sort keys change from release to release. If a primary index is detected to be in this state then JetAttachDatabase will always fail with JET_err.PrimaryIndexCorrupted. If any secondary indexes are detected to be in this state then there are two possible outcomes. If AttachDatabaseGrbit.DeleteCorruptIndexes was passed to JetAttachDatabase then these indexes will be deleted and JET_wrnCorruptIndexDeleted will be returned from JetAttachDatabase. These indexes will need to be recreated by your application. If AttachDatabaseGrbit.DeleteCorruptIndexes was not passed to JetAttachDatabase then the call will fail with JET_errSecondaryIndexCorrupted. |
| EventSourceKey | This parameter can be used to control which event log the database engine uses for its event log messages. By default, all event log messages will go to the Application event log. If the registry key name for another event log is configured then the event log messages will go there instead. |
| NoInformationEvent | When this parameter is true, informational event log messages that would ordinarily be generated by the database engine will be suppressed. |
| EventLoggingLevel | Configures the detail level of eventlog messages that are emitted to the eventlog by the database engine. Higher numbers will result in more detailed eventlog messages. |
| DeleteOutOfRangeLogs | Delete the log files that are not matching (generation wise) during soft recovery. |
| CacheSizeMin | This parameter configures the minimum size of the database page cache. The size is in database pages. |
| PreferredVerPages | This parameter represents a threshold relative to MaxVerPages that controls the discretionary use of version pages by the database engine. If the size of the version store exceeds this threshold then any information that is only used for optional background tasks, such as reclaiming deleted space in the database, is instead sacrificed to preserve room for transactional information. |
| DatabasePageSize | This parameter configures the page size for the database. The page size is the smallest unit of space allocation possible for a database file. The database page size is also very important because it sets the upper limit on the size of an individual record in the database. Only one database page size is supported per process at this time. This means that if you are in a single process that contains different applications that use the database engine then they must all agree on a database page size. |
| ErrorToString | This parameter can be used to convert a JET_ERR into a string. This should only be used with JetGetSystemParameter. |
| RuntimeCallback | Configures the engine with a JET_CALLBACK delegate. This callback may be called for the following reasons: FreeCursorLS, FreeTableLS or Null. See JetSetLS(JET_SESID, JET_TABLEID, JET_LS, LsGrbit) for more information. This parameter cannot currently be retrieved. |
| CleanupMismatchedLogFiles | This parameter controls the outcome of JetInit when the database engine is configured to start using transaction log files on disk that are of a different size than what is configured. Normally, JetInit(JET_INSTANCE) will successfully recover the databases but will fail with LogFileSizeMismatchDatabasesConsistent to indicate that the log file size is misconfigured. However, when this parameter is set to true then the database engine will silently delete all the old log files, start a new set of transaction log files using the configured log file size. This parameter is useful when the application wishes to transparently change its transaction log file size yet still work transparently in upgrade and restore scenarios. |
| ExceptionAction | This parameter controls what happens when an exception is thrown by the database engine or code that is called by the database engine. When set to JET_ExceptionMsgBox, any exception will be thrown to the Windows unhandled exception filter. This will result in the exception being handled as an application failure. The intent is to prevent application code from erroneously trying to catch and ignore an exception generated by the database engine. This cannot be allowed because database corruption could occur. If the application wishes to properly handle these exceptions then the protection can be disabled by setting this parameter to JET_ExceptionNone. |
| CreatePathIfNotExist | When this parameter is set to true then any folder that is missing in a file system path in use by the database engine will be silently created. Otherwise, the operation that uses the missing file system path will fail with JET_err.InvalidPath. |
| OneDatabasePerSession | When this parameter is true then only one database is allowed to be opened using JetOpenDatabase by a given session at one time. The temporary database is excluded from this restriction. |
| MaxInstances | This parameter controls the maximum number of instances that can be created in a single process. |
| VersionStoreTaskQueueMax | This parameter controls the number of background cleanup work items that can be queued to the database engine thread pool at any one time. |
See also
Reference
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