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ILog::ReadRecordPrefix method (txlogpub.h)

  • Article

Reads an initial part of a record from the log.

Syntax

HRESULT ReadRecordPrefix(
  [in]      LSN   lsnToRead,
  [in, out] LSN   *plsnPrev,
  [in, out] LSN   *plsnNext,
  [out]     BYTE  *pbData,
  [in, out] ULONG *pcbData,
  [out]     ULONG *pcbRecord
);

Parameters

[in] lsnToRead

The LSN of the record to be read.

[in, out] plsnPrev

A pointer to the LSN of the previous record (the record immediately preceding the record to read). You may pass NULL if the LSN of the previous record is not needed. This parameter is 0 if there is no previous record in the log or if an error occurs.

[in, out] plsnNext

A pointer to the LSN of the next record (the record immediately following the record to read). You may pass NULL if the LSN of the next record is not needed. This parameter is MAXLSN (0x7FFFFFFFFFFFFFFF) if there is no next record in the log. This parameter is 0 if an error occurs.

[out] pbData

A pointer to a buffer into which the record data is to be read.

[in, out] pcbData

A pointer to a variable that contains the size in bytes of the buffer on input, and will contain the size in bytes of the record data read on return.

[out] pcbRecord

A pointer to a variable that will contain the size in bytes of the entire record on return. You may pass NULL if the size of the entire record is not needed.

Return value

This method can return the following values, as well as other HRESULT values.

Return code Description
S_OK
 The record was successfully read from the log.
XACT_E_INVALIDLSN
 lsnToRead is outside of the current limits of the log. See ILog::GetLogLimits.
E_INVALIDARG
 lsnToRead is within the current limits of the log, but it is not the LSN of a record in the log.

Remarks

Although records appended to the log using ILog::AppendRecord may be concatenated from multiple BLOBs, ReadRecordPrefix returns the record as a single opaque blob of data. ILog provides no method to extract individual BLOBs from the record. It is the responsibility of the caller to parse the data in records returned by ReadRecordPrefix.

Requirements

Requirement Value
Minimum supported client Windows XP [desktop apps only]
Minimum supported server Windows Server 2003 [desktop apps only]
Target Platform Windows
Header txlogpub.h

See also

ILog