Applying InnoDB snapshot

Detailed revision comments:

r6467 | inaam | 2010-01-14 20:46:00 +0200 (Thu, 14 Jan 2010) | 10 lines
branches/zip rb://226

log_sys->written_to_all_lsn does not accurately represent the LSN
upto which write and flush has taken place. Under a race condition
it can fall behind log_sys->flushed_to_disk_lsn which is accurate.
Besides written_to_all_lsn is redundant as currently InnoDB supports
only one log group.

Approved by: Heikki

storage/innodb_plugin/include/log0log.h

@@ -825,7 +825,17 @@ struct log_struct{
 					written to some log group; for this to
 					be advanced, it is enough that the
 					write i/o has been completed for all
-					log groups */
+					log groups.
+					Note that since InnoDB currently
+					has only one log group therefore
+					this value is redundant. Also it
+					is possible that this value
+					falls behind the
+					flushed_to_disk_lsn transiently.
+					It is appropriate to use either
+					flushed_to_disk_lsn or
+					write_lsn which are always
+					up-to-date and accurate. */
 	ib_uint64_t	write_lsn;	/*!< end lsn for the current running
 					write */
 	ulint		write_end_offset;/*!< the data in buffer has

storage/innodb_plugin/log/log0log.c

@@ -2013,7 +2013,7 @@ log_checkpoint(
 		return(TRUE);
 	}
 
-	ut_ad(log_sys->written_to_all_lsn >= oldest_lsn);
+	ut_ad(log_sys->flushed_to_disk_lsn >= oldest_lsn);
 
 	if (log_sys->n_pending_checkpoint_writes > 0) {
 		/* A checkpoint write is running */