gsyncd / geo-rep : failover/failback

This commit is based on Venky Shankar <vshankar@>'s
original implementation. Let us first quote Venky's
description, then we summarize changes to his work.

------
First version of failover/failback.

Failback mechanism uses two exclusive modes:
  * blind-sync
    This mode works with xtime pairs (both master and slave) to
    identify candidated to sync the original master from the slave

  * wrapup-sync
    This mode is similar to the normal working of gsyncd except
    that orphaned entities in the gluster volume are not assigned
    xtimes. This prevents un-necessary transfer of data for such
    entities.

Modes can be enabled via:

  gluster volume geo-replication M S config special_sync_mode blind
  gluster volume geo-replication M S config special_sync_mode wrapup

To turn off the special modes (i.e. to revert to normal gsyncd behaviour) use:

  gluster volume geo-replication colon-d0 192.168.1.2::colon-d config \!special_sync_mode
------

Code has been refactored to meet following goals:

- make checkpointing work with special sync modes
- move out sync mode related conditionals from the crawl
  loop and make all decisions to be made at startup
  time
- be intrusive to the crawl loop to smallest possible degree
  (we will have to change/revisit it for other reasons,
  and the complexity of that should not increase)

So, xtime parsing/updating/evaluation that's specific to
the certain special modes are represented as mixin classes;
basic operation logic is in an abstract base class.
On startup, special-sync-mode tunable is dynamically dispatched
to the corresponding mixin and the actual master class is
derived from the chosen mixin and the ABS.

Change-Id: Ic9b8448f31ad4239a8200dc689f7d713662a67de
BUG: 830497
Signed-off-by: Csaba Henk <csaba@redhat.com>
Reviewed-on: http://review.gluster.com/3541
Tested-by: Gluster Build System <jenkins@build.gluster.com>
Reviewed-by: Venky Shankar <vshankar@redhat.com>

1 files changed, 29 insertions, 2 deletions

diff --git a/xlators/features/marker/utils/syncdaemon/resource.py b/xlators/features/marker/utils/syncdaemon/resource.py
index c4cd19c9fb7..7e62fd48ca9 100644
--- a/xlators/features/marker/utils/syncdaemon/resource.py
+++ b/xlators/features/marker/utils/syncdaemon/resource.py
@@ -17,7 +17,7 @@ from select import error as selecterror
 from gconf import gconf
 import repce
 from repce import RepceServer, RepceClient
-from master import GMaster
+from  master import gmaster_builder
 import syncdutils
 from syncdutils import GsyncdError, select, privileged
 
@@ -359,11 +359,37 @@ class Server(object):
                 raise
 
     @classmethod
+    def xtime_vec(cls, path, *uuids):
+        """vectored version of @xtime
+
+        accepts a list of uuids and returns a dictionary
+        with uuid as key(s) and xtime as value(s)
+        """
+        xt = {}
+        for uuid in uuids:
+            xtu = cls.xtime(path, uuid)
+            if xtu == ENODATA:
+                xtu = None
+            if isinstance(xtu, int):
+                return xtu
+            xt[uuid] = xtu
+        return xt
+
+    @classmethod
     @_pathguard
     def set_xtime(cls, path, uuid, mark):
         """set @mark as xtime for @uuid on @path"""
         Xattr.lsetxattr(path, '.'.join([cls.GX_NSPACE, uuid, 'xtime']), struct.pack('!II', *mark))
 
+    @classmethod
+    def set_xtime_vec(cls, path, mark_dct):
+        """vectored (or dictered) version of set_xtime
+
+        ignore values that match @ignore
+        """
+        for u,t in mark_dct.items():
+            cls.set_xtime(path, u, t)
+
     @staticmethod
     @_pathguard
     def setattr(path, adct):
@@ -604,6 +630,7 @@ class GLUSTER(AbstractUrl, SlaveLocal, SlaveRemote):
                     if x[0] > now:
                         logging.debug("volinfo[%s] expires: %d (%d sec later)" % \
                                       (d['uuid'], x[0], x[0] - now))
+                        d['timeout'] = x[0]
                         dict_list.append(d)
                     else:
                         try:
@@ -820,7 +847,7 @@ class GLUSTER(AbstractUrl, SlaveLocal, SlaveRemote):
         - else do that's what's inherited
         """
         if args:
-            GMaster(self, args[0]).crawl_loop()
+            gmaster_builder()(self, args[0]).crawl_loop()
         else:
             sup(self, *args)