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Summary:
Halo Geo-replication is a feature which allows Gluster or NFS clients to write locally to their region (as defined by a latency "halo" or threshold if you like), and have their writes asynchronously propagate from their origin to the rest of the cluster. Clients can also write synchronously to the cluster simply by specifying a halo-latency which is very large (e.g. 10seconds) which will include all bricks.
In other words, it allows clients to decide at mount time if they desire synchronous or asynchronous IO into a cluster and the cluster can support both of these modes to any number of clients simultaneously.
There are a few new volume options due to this feature:
halo-shd-latency: The threshold below which self-heal daemons will
consider children (bricks) connected.
halo-nfsd-latency: The threshold below which NFS daemons will consider
children (bricks) connected.
halo-latency: The threshold below which all other clients will
consider children (bricks) connected.
halo-min-replicas: The minimum number of replicas which are to
be enforced regardless of latency specified in the above 3 options.
If the number of children falls below this threshold the next
best (chosen by latency) shall be swapped in.
New FUSE mount options:
halo-latency & halo-min-replicas: As descripted above.
This feature combined with multi-threaded SHD support (D1271745) results in some pretty cool geo-replication possibilities.
Operational Notes:
- Global consistency is gaurenteed for synchronous clients, this is provided by the existing entry-locking mechanism.
- Asynchronous clients on the other hand and merely consistent to their region. Writes & deletes will be protected via entry-locks as usual preventing concurrent writes into files which are undergoing replication. Read operations on the other hand should never block.
- Writes are allowed from _any_ region and propagated from the origin to all other regions. The take away from this is care should be taken to ensure multiple writers do not write the same files resulting in a gfid split-brain which will require resolution via split-brain policies (majority, mtime & size). Recommended method for preventing this is using the nfs-auth feature to define which region for each share has RW permissions, tiers not in the origin region should have RO perms.
TODO:
- Synchronous clients (including the SHD) should choose clients from their own region as preferred sources for reads. Most of the plumbing is in place for this via the child_latency array.
- Better GFID split brain handling & better dent type split brain handling (i.e. create a trash can and move the offending files into it).
- Tagging in addition to latency as a means of defining which children you wish to synchronously write to
Test Plan:
- The usual suspects, clang, gcc w/ address sanitizer & valgrind
- Prove tests
Reviewers: jackl, dph, cjh, meyering
Reviewed By: meyering
Subscribers: ethanr
Differential Revision: https://phabricator.fb.com/D1272053
Tasks: 4117827
Change-Id: I694a9ab429722da538da171ec528406e77b5e6d1
Signed-off-by: Kevin Vigor <kvigor@fb.com>
Reviewed-on: http://review.gluster.org/16099
NetBSD-regression: NetBSD Build System <jenkins@build.gluster.org>
Smoke: Gluster Build System <jenkins@build.gluster.org>
CentOS-regression: Gluster Build System <jenkins@build.gluster.org>
Reviewed-by: Shreyas Siravara <sshreyas@fb.com>
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git@forge.gluster.org:~schafdog/glusterfs-core/osx-glusterfs
Working functionality on MacOSX
- GlusterD (management daemon)
- GlusterCLI (management cli)
- GlusterFS FUSE (using OSXFUSE)
- GlusterNFS (without NLM - issues with rpc.statd)
Change-Id: I20193d3f8904388e47344e523b3787dbeab044ac
BUG: 1089172
Signed-off-by: Harshavardhana <harsha@harshavardhana.net>
Signed-off-by: Dennis Schafroth <dennis@schafroth.com>
Tested-by: Harshavardhana <harsha@harshavardhana.net>
Tested-by: Dennis Schafroth <dennis@schafroth.com>
Reviewed-on: http://review.gluster.org/7503
Tested-by: Gluster Build System <jenkins@build.gluster.com>
Reviewed-by: Anand Avati <avati@redhat.com>
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The argument to the timespec_adjust_delta() function introudced in
commit 6836118b21 needs to be passed by reference rather than by value
for the function to do it's job.
BUG: 1028663
Change-Id: I62a3636906e67ed35b7786e9553f6819b48f3626
Signed-off-by: Ravishankar N <ravishankar@redhat.com>
Reviewed-on: http://review.gluster.org/6243
Tested-by: Gluster Build System <jenkins@build.gluster.com>
Reviewed-by: Anand Avati <avati@redhat.com>
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gettimeofday() returns the current wall clock time and timezone.
Using these functions in order to measure the passage of time
(how long an operation took) therefore seems like a no-brainer.
This time suffer's from some limitations:
a. They have a low resolution: “High-performance” timing by
definition, requires clock resolutions into the microseconds
or better.
b. They can jump forwards and backwards in time: Computer
clocks all tick at slightly different rates, which causes
the time to drift. Most systems have NTP enabled which
periodically adjusts the system clock to keep them in sync
with “actual” time. The adjustment can cause the clock to
suddenly jump forward (artificially inflating your timing
numbers) or jump backwards (causing your timing calculations
to go negative or hugely positive). In such cases timer
thread could go into an infinite loop.
From 'man gettimeofday':
----------
..
..
The time returned by gettimeofday() is affected by discontinuous
jumps in the system time (e.g., if the system administrator manually
changes the system time). If you need a monotonically increasing
clock, see clock_gettime(2).
..
..
----------
Rationale:
For calculating interval timing for Timer thread, all that’s
needed should be clock as a simple counter that increments
at a stable rate.
This is necessary to avoid the jumps which are caused by using
"wall time", this counter must be monotonic that can never
“tick” backwards, ever.
Change-Id: I701d31e71a85a73d21a6c5cd15583e7a5a645eeb
BUG: 1017993
Signed-off-by: Harshavardhana <harsha@harshavardhana.net>
Reviewed-on: http://review.gluster.org/6070
Tested-by: Gluster Build System <jenkins@build.gluster.com>
Reviewed-by: Anand Avati <avati@redhat.com>
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