features/changelog: Consider only changelog on/off as changelog breakage

Earlier, both chagelog on/off and brick restart were considered
to be changelog breakage and treated as changelog not being
continuous. As a result, new HTIME.TSTAMP file was created on
both the above cases. Now the change is made such that only
on changelog enable/disable, the changelog is considered to be
discontinuous. New HTIME.TSTAMP file is not created on brick
restart, the changelogs files are appended to last HTIME.TSTAMP
file.

Treating changelog as continuous in above scenario is important
as changelog history API will fail otherwise. It can successfully
get changes between start and end timestamps only when changelog
is continuous (Changelogs in single HTIME.TSTAMP file are treated
as continuous). Without this change, changelog history API would
fail, and it would become necessary to fallback to other mechanisms
like xsync FSCrawl in case geo-rep to detect changes in this time
window. But Xsync FSCrawl would not be applicable to other
consumers like glusterfind.

Rationale:
1. In plain distributed volume, if brick goes down, no I/O can
   happen onto the brick. Hence changelog is intact with data
   on disk.
2. In distributed replicate volume, if brick goes down, since
   self-heal traffic is captured in changelog. Eventually,
   I/O happened whend brick down is captured in changelog.

BUG: 1217944
Change-Id: Ifa6d932818fe1a3a914e87ac84f1d2ded01c1288
Signed-off-by: Kotresh HR <khiremat@redhat.com>
Reviewed-on: http://review.gluster.org/10222
Reviewed-on: http://review.gluster.org/10507
Tested-by: Gluster Build System <jenkins@build.gluster.com>
Reviewed-by: Aravinda VK <avishwan@redhat.com>
Reviewed-by: Vijay Bellur <vbellur@redhat.com>

1 files changed, 3 insertions, 1 deletions

diff --git a/xlators/features/changelog/src/changelog-helpers.h b/xlators/features/changelog/src/changelog-helpers.h
index 765d5fd878b..b552c308e0f 100644
--- a/xlators/features/changelog/src/changelog-helpers.h
+++ b/xlators/features/changelog/src/changelog-helpers.h
@@ -432,7 +432,9 @@ int
 htime_update (xlator_t *this, changelog_priv_t *priv,
               unsigned long ts, char * buffer);
 int
-htime_open (xlator_t *this, changelog_priv_t * priv, unsigned long ts);
+htime_open (xlator_t *this, changelog_priv_t *priv, unsigned long ts);
+int
+htime_create (xlator_t *this, changelog_priv_t *priv, unsigned long ts);
 
 /* Geo-Rep snapshot dependency changes */
 void