I/O Parameters

Applies to: Windows | Windows Server

I/O Parameters

This topic contains parameters that are used for input and output (I/O).

JET_paramAccessDeniedRetryPeriod
53

Windows XP and later:  This parameter configures the duration of time (in milliseconds) that the database engine will use to access a file that is locked before failing with JET_errFileAccessDenied. This time delay is designed to work around anti-virus software that may hold some of the database engine's files open briefly after they are closed.

Note  As a result of the above retry logic, any attempt to attach to a database or use a log file that is already in use by the database engine will result in a delay of this size before the API call returns a (legitimate) failure. This parameter can be used to turn down that delay in case this is a common scenario.

JET_paramCreatePathIfNotExist
100

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_errInvalidPath.

JET_paramEnableFileCache
126

When this parameter is True, the database engine will use the Windows file cache as a read cache for all of its various files. It will also use it as a write cache for the temporary database or for databases that are opened with recovery disabled. The database engine must disable write caching for ordinary databases, transaction log files, and checkpoint files to protect the transactional integrity of the databases.

It is important to note that the use of the Windows file cache will add a second layering of caching for database files. The database cache will still use its own memory to cache the database files. The intent of this mode is to allow the application to configure the database engine with a small dedicated cache and to allow Windows to donate spare memory to further improve the caching of database data.

JET_paramIOPriority
152

This parameter controls how ESE handles I/O operations. The values can be set to 0 (JET_IOPriorityNormal) for normal operation, or 1 (JET_IOPriorityLow) for low priority operation. When the priority is set to JET_IOPriorityLow, ESE uses the new thread I/O priority functionality available in Windows Vista to reduce the I/O priority on the thread so that subsequent I/O operations are issued at the new low priority.

Windows Vista:  JET_paramIOPriority is introduced in Windows Vista.

JET_paramOutstandingIOMax
30

This parameter controls how many database file I/Os can be queued in the host operating system at one time.

A larger value for this parameter can significantly help the performance of a large database application.

Windows XP and Windows Server 2003:  This parameter is ignored on Windows XP and Windows Server 2003 and does not affect the operation of the database engine.

JET_paramMaxCoalesceReadSize
164

Maximum number of bytes that can be grouped for a coalesced read operation.

JET_paramMaxCoalesceWriteSize
165

Maximum number of bytes that can be grouped for a coalesced write operation.

JET_paramMaxCoalesceReadGapSize
166

Maximum number of bytes that can be gapped for a coalesced write I/O operation.

JET_paramMaxCoalesceWriteGapSize
167

Max number of bytes that can be gapped for a coalesced read I/O operation.

Requirements

See Also

JetCreateInstance
JetInit