JetPrereadIndexRanges Function
Applies to: Windows | Windows Server
The JetPrereadIndexRanges function prereads indexes to improve the performance.
The JetPrereadIndexRanges function was introduced in the Windows 8 operating system.
JET_ERR JetPrereadIndexRanges(
__in const JET_SESID sesid,
__in const JET_TABLEID tableid,
__in_ecount(cIndexRanges) const JET_INDEX_RANGE* const rgIndexRanges,
__in const unsigned long cIndexRanges,
__out_opt unsigned long* const pcRangesPreread,
__in_ecount(ccolumnidPreread) const JET_COLUMNID* const rgcolumnidPreread,
__in const unsigned long ccolumnidPreread,
__in const JET_GRBIT grbit
);
Parameters
sesid
The database session context to use for the API call.
tableid
The table to issue the prereads against.
rgIndexRanges
The key ranges to preread.
cIndexRanges
The number of key ranges to preread, determined by the number of elements in rgIndexRanges.
pcRangesPreread
The number of key ranges that were actually preread.
rgcolumnidPreread
List of column IDs for long value columns to preread. By default, only the on-page record is preread. If Off-page long value columns need to be preread, their column IDs need to be passed via this parameter.
ccolumnidPreread
The number of column IDs for long value columns to preread, determined by the number of elements in rgcolumnidPreread.
grbit
A group of bits that specifies zero or more of the preread direction values listed in the following table.
Value |
Meaning |
|---|---|
Forward |
Preread forward. |
Backwards |
Preread backward. |
FirstPageOnly |
Preread only the first page of any long column. |
NormalizedKey |
Normalized key/bookmark provided instead of column value. |
Return value
This function returns the JET_ERR data type with one of the return codes listed in the following table. For more information about the possible Extensible Storage Engine (ESE) errors, see Extensible Storage Engine Errors and Error Handling Parameters.
Return code |
Description |
|---|---|
JET_errSuccess |
The operation completed successfully. |
Remarks
If the records with the specified key ranges are not in the buffer cache, you should start asynchronous reads to bring the records into the database buffer cache.
Requirements
| Requirement | Value |
|---|---|
Client |
Requires Windows 8. |
Server |
Requires Windows Server 2012. |
Header |
Declared in Esent.h. |
Library |
Use ESENT.lib. |
DLL |
Requires ESENT.dll. |