[PATCH v4 2/3] vinyl: simplify vylog recovery from backup

[Vladimir Davydov <vdavydov.dev@gmail.com>]

Since we don't create snapshot files for vylog, but instead append
records written after checkpoint to the same file, we have to use the
previous vylog file for backup (see vy_log_backup_path()). So when
recovering from a backup we need to rotate the last vylog to keep vylog
and checkpoint signatures in sync. Currently, we do it on recovery
completion and we use vy_log_create() instead of vy_log_rotate() for it.
This is done so that we can reuse the context that was used for recovery
instead of rereading vylog for rotation. Actually, there's no point in
this micro-optimization, because we rotate vylog only when recovering
from a backup. Let's remove it and use vy_log_rotate() for this.

Needed for #461
---
 src/box/vy_log.c | 59 +++++++++++++++++++++-----------------------------------
 1 file changed, 22 insertions(+), 37 deletions(-)

diff --git a/src/box/vy_log.c b/src/box/vy_log.c
index c20f8038..10648106 100644
--- a/src/box/vy_log.c
+++ b/src/box/vy_log.c
@@ -184,6 +184,12 @@ static int
 vy_recovery_process_record(struct vy_recovery *recovery,
 			   const struct vy_log_record *record);
 
+static int
+vy_log_create(const struct vclock *vclock, struct vy_recovery *recovery);
+
+int
+vy_log_rotate(const struct vclock *vclock);
+
 /**
  * Return the name of the vylog file that has the given signature.
  */
@@ -883,10 +889,11 @@ vy_log_begin_recovery(const struct vclock *vclock)
 	if (xdir_scan(&vy_log.dir) < 0 && errno != ENOENT)
 		return NULL;
 
-	struct vclock vy_log_vclock;
-	vclock_create(&vy_log_vclock);
-	if (xdir_last_vclock(&vy_log.dir, &vy_log_vclock) >= 0 &&
-	    vclock_compare(&vy_log_vclock, vclock) > 0) {
+	if (xdir_last_vclock(&vy_log.dir, &vy_log.last_checkpoint) < 0)
+		vclock_copy(&vy_log.last_checkpoint, vclock);
+
+	int cmp = vclock_compare(&vy_log.last_checkpoint, vclock);
+	if (cmp > 0) {
 		/*
 		 * Last vy_log log is newer than the last snapshot.
 		 * This can't normally happen, as vy_log is rotated
@@ -896,21 +903,27 @@ vy_log_begin_recovery(const struct vclock *vclock)
 		diag_set(ClientError, ER_MISSING_SNAPSHOT);
 		return NULL;
 	}
+	if (cmp < 0) {
+		/*
+		 * Last vy_log log is older than the last snapshot.
+		 * This happens if we are recovering from a backup.
+		 * Rotate the log to keep its signature in sync with
+		 * checkpoint.
+		 */
+		if (vy_log_rotate(vclock) != 0)
+			return NULL;
+	}
 
 	struct vy_recovery *recovery;
-	recovery = vy_recovery_new(vclock_sum(&vy_log_vclock), 0);
+	recovery = vy_recovery_new(vclock_sum(&vy_log.last_checkpoint), 0);
 	if (recovery == NULL)
 		return NULL;
 
 	vy_log.next_id = recovery->max_id + 1;
 	vy_log.recovery = recovery;
-	vclock_copy(&vy_log.last_checkpoint, vclock);
 	return recovery;
 }
 
-static int
-vy_log_create(const struct vclock *vclock, struct vy_recovery *recovery);
-
 int
 vy_log_end_recovery(void)
 {
@@ -931,34 +944,6 @@ vy_log_end_recovery(void)
 		return -1;
 	}
 
-	/*
-	 * On backup we copy files corresponding to the most recent
-	 * checkpoint. Since vy_log does not create snapshots of its log
-	 * files, but instead appends records written after checkpoint
-	 * to the most recent log file, the signature of the vy_log file
-	 * corresponding to the last checkpoint equals the signature
-	 * of the previous checkpoint. So upon successful recovery
-	 * from a backup we need to rotate the log to keep checkpoint
-	 * and vy_log signatures in sync.
-	 */
-	struct vclock *vclock = vclockset_last(&vy_log.dir.index);
-	if (vclock == NULL ||
-	    vclock_compare(vclock, &vy_log.last_checkpoint) != 0) {
-		vclock = malloc(sizeof(*vclock));
-		if (vclock == NULL) {
-			diag_set(OutOfMemory, sizeof(*vclock),
-				 "malloc", "struct vclock");
-			return -1;
-		}
-		vclock_copy(vclock, &vy_log.last_checkpoint);
-		xdir_add_vclock(&vy_log.dir, vclock);
-		if (vy_log_create(vclock, vy_log.recovery) < 0) {
-			diag_log();
-			say_error("failed to write `%s'",
-				  vy_log_filename(vclock_sum(vclock)));
-			return -1;
-		}
-	}
 	xdir_collect_inprogress(&vy_log.dir);
 	vy_log.recovery = NULL;
 	return 0;
-- 
2.11.0