stasis-aries-wal/stasis/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 Everything in this file cores on failure (no error handling yet)
 * @todo logWriter is optimized for forward operation, scanning backwards 
 *       (as in abort()) is very slow.  Perhaps we should maintian a 
 *       'write behind' buffer?
 *
 * $Id$
 * 
 */

#ifndef __LOGWRITER_H__
#define __LOGWRITER_H__

#include <stasis/common.h>
#include <stasis/logger/logEntry.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_LogWriter();

/** 
   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_LogWriter();

/**
   Truncates the log file.  In the single-threaded case, this works as
   follows:

   First, the LSN passed to this function, minus sizeof(lsn_t) is
   written to a new file, called logfile.txt~.  (If logfile.txt~
   already exists, then it is truncated.)

   Next, the contents of the log, starting with the LSN passed into
   this function are copied to logfile.txt~

   Finally, logfile.txt~ is moved on top of logfile.txt

   As long as the move system call is atomic, this function should
   maintain the system's durability.

   The multithreaded case is a bit more complicated, as we need
   to deal with latching:

   With no lock, copy the log.  Upon completion, if the log has grown,
   then copy the part that remains.  Next, obtain a read/write latch
   on the logfile, and copy any remaining portions of the log.
   Perform the move, and release the latch.

*/

int truncateLog_LogWriter(lsn_t);


/** 
    @return The LSN of the first entry in the log file.  (If the file
    is empty, this returns the LSN of the log entry that would be
    created if writeLogEntry were called.)
*/
lsn_t firstLogEntry();
/**
  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 only exists because the tests use it...once the logfile
        name isn't hardcoded, remove this function.
*/
void deleteLogWriter();

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

   @param LSN the LSN of the entry that will be read.
*/
LogEntry * readLSNEntry_LogWriter(lsn_t LSN);
static inline lsn_t nextEntry_LogWriter(const LogEntry * e) { 
  return e->LSN + sizeofLogEntry(e) + sizeof(lsn_t);
}

extern int logWriter_isDurable;

long sizeofInternalLogEntry_LogWriter(const LogEntry * e);

END_C_DECLS

#endif /* __LLADD_LOGGER_LOGWRITER_H */