WT-2338 Add a comment in log pre-allocation

Explaining why we can't pre-allocate while a hot backup cursor is open.

1 files changed, 6 insertions, 0 deletions

diff --git a/src/conn/conn_log.c b/src/conn/conn_log.c
index 5e44436d0eb..0100fdd5b52 100644
--- a/src/conn/conn_log.c
+++ b/src/conn/conn_log.c
@@ -741,6 +741,12 @@ __log_server(void *arg)
 			 * Perform log pre-allocation.
 			 */
 			if (conn->log_prealloc > 0) {
+				/*
+				 * Log file pre-allocation is disabled when a
+				 * hot backup cursor is open because we have
+				 * agreed not to rename or remove any files in
+				 * the database directory.
+				 */
 				WT_ERR(__wt_readlock(
 				    session, conn->hot_backup_lock));
 				locked = true;