stasis-aries-wal/lladd/logger/logWriter.h

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---*/

/**
 * @file
 * 
 * New version of logstreamer; designed to work with logEntry, and has
 * a simplified API.
 *
 * logstreamer is the implementation of writing the log tail
 * It must be bufferred -- in that when something is written to the log tail it
 * is not immediately written to disk, but rather just to memory. But
 * logstreamer must be able to force flush to disk, which will be done when a
 * commit log entry is written to the log tail
 * 
 * Note: using the stdio FILEs for this, and by default it is "fully" buffered.
 * The log tail may be flushed to disk without an explicit call to fflush (when
 * the program terminates, the file closes), but this is acceptable because it
 * never hurts to have more flushes to disk, as long as it doesn't hurt
 * performance.
 *
 * @todo CORRECTNESS: We currently assume that there are no partial entries in the log!
 * @todo Everything in this file cores on failure (no error handling yet)
 * @todo All of the logWriter calls should be reentrant.
 *
 * $Id$
 * 
 */

#ifndef __LOGWRITER_H__
#define __LOGWRITER_H__

#include "logEntry.h"
#include <lladd/constants.h>
#include <lladd/common.h>

BEGIN_C_DECLS
/**
  start a new log stream by opening the log file for reading

  returns 0 on success, or an error code define above

*/
int openLogWriter();

/**
   
  @param e Pointer to a log entry.  After the call, e->LSN will be set appropriately.  If e's xid is set to -1, then this call has no effect (and e's LSN will be set to -1.)

  returns 0 on success, or an error code defined above
*/
int writeLogEntry(LogEntry * e);

/**
  flush the entire log (tail) that is currently in memory to disk
*/
void syncLog();

/** 
   Return the highest LSN that is known to be on disk.  (Currently, we
   only know if an LSN is on disk if we've written that LSN before a
   call to syncLog().

   Note: This function might not return an LSN corresponding to a real
   log entry, but it will definitely return one that is greater than
   or equal to the LSN of a log entry that has been forced to disk,
   and is less than the LSN of all log entries that might not have
   been forced to disk.
*/
lsn_t flushedLSN();

/**
  Close the log stream
*/
void closeLogWriter();

/**
  Actually deletes the log file that may have been written to disk! Danger!!
  Only use after calling closeLogStream AND you are sure there are no active (or
  future active) transactions!

  @todo This is in here now for completeness, but once we implement
  log truncation, it should leave.
*/
void deleteLogWriter();

/**
   Read a log entry at a particular LSN.

   @param the LSN of the entry that will be read.
*/
LogEntry * readLSNEntry(lsn_t LSN);

END_C_DECLS

#endif /* __LLADD_LOGGER_LOGWRITER_H */