[RFC PATCH 06/12] box: refactor hot standby recovery

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

Currently, we start a hot standby fiber even if not in hot standby mode
(see recovery_follow_local). And we scan the wal directory twice - first
time in recovery_follow_local(), second time in recovery_finalize().
Let's factor out recover_remaining_wals() from those functions and call
it explicitly. And let's start call follow_local() and stop_local() only
if in hot standby mode.

Needed for #461
---
 src/box/box.cc      | 12 +++++++-----
 src/box/recovery.cc | 12 ++----------
 src/box/recovery.h  |  2 +-
 3 files changed, 10 insertions(+), 16 deletions(-)

diff --git a/src/box/box.cc b/src/box/box.cc
index e1bf3934..9105ed19 100644
--- a/src/box/box.cc
+++ b/src/box/box.cc
@@ -1887,16 +1887,17 @@ box_cfg_xc(void)
 				&last_checkpoint_vclock);
 
 		engine_begin_final_recovery_xc();
-		recovery_follow_local(recovery, &wal_stream.base, "hot_standby",
-				      cfg_getd("wal_dir_rescan_delay"));
-		title("hot_standby");
-
+		recover_remaining_wals(recovery, &wal_stream.base, NULL, true);
 		/*
 		 * Leave hot standby mode, if any, only
 		 * after acquiring the lock.
 		 */
 		if (wal_dir_lock < 0) {
+			title("hot_standby");
 			say_info("Entering hot standby mode");
+			recovery_follow_local(recovery, &wal_stream.base,
+					      "hot_standby",
+					      cfg_getd("wal_dir_rescan_delay"));
 			while (true) {
 				if (path_lock(cfg_gets("wal_dir"),
 					      &wal_dir_lock))
@@ -1905,9 +1906,10 @@ box_cfg_xc(void)
 					break;
 				fiber_sleep(0.1);
 			}
+			recovery_stop_local(recovery);
 			box_bind();
 		}
-		recovery_finalize(recovery, &wal_stream.base);
+		recovery_finalize(recovery);
 		engine_end_recovery_xc();
 
 		/* Check replica set UUID. */
diff --git a/src/box/recovery.cc b/src/box/recovery.cc
index cf348d29..5ef1f979 100644
--- a/src/box/recovery.cc
+++ b/src/box/recovery.cc
@@ -313,12 +313,8 @@ recover_current_wal:
 }
 
 void
-recovery_finalize(struct recovery *r, struct xstream *stream)
+recovery_finalize(struct recovery *r)
 {
-	recovery_stop_local(r);
-
-	recover_remaining_wals(r, stream, NULL, true);
-
 	recovery_close_log(r);
 
 	/*
@@ -490,6 +486,7 @@ hot_standby_f(va_list ap)
 
 		subscription.events = 0;
 	}
+	recover_remaining_wals(r, stream, NULL, true);
 	return 0;
 }
 
@@ -498,11 +495,6 @@ recovery_follow_local(struct recovery *r, struct xstream *stream,
 		      const char *name, ev_tstamp wal_dir_rescan_delay)
 {
 	/*
-	 * Scan wal_dir and recover all existing at the moment xlogs.
-	 * Blocks until finished.
-	 */
-	recover_remaining_wals(r, stream, NULL, true);
-	/*
 	 * Start 'hot_standby' background fiber to follow xlog changes.
 	 * It will pick up from the position of the currently open
 	 * xlog.
diff --git a/src/box/recovery.h b/src/box/recovery.h
index 3a950e47..6aba922b 100644
--- a/src/box/recovery.h
+++ b/src/box/recovery.h
@@ -76,7 +76,7 @@ void
 recovery_stop_local(struct recovery *r);
 
 void
-recovery_finalize(struct recovery *r, struct xstream *stream);
+recovery_finalize(struct recovery *r);
 
 #if defined(__cplusplus)
 } /* extern "C" */
-- 
2.11.0