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Le 04/03/2016 10:56, Krutika Dhananjay
a écrit :
Hi,
So up until in 3.5.x, there was a read child selection mode
called 'first responder' where the brick that responds first
for a particular client becomes the read child.
After the replication module was rewritten for the most
part from 3.6.0, this mode was removed.
There exists a workaround, though. Could you share the
output of `gluster volume info <VOL>`?
It gives (note: this volume is not used apart for testing so I can
"play" with it):
Volume Name: HOME
Type: Replicate
Volume ID: ea90bcaf-990d-436a-b4fa-8fa20d67f924
Status: Started
Number of Bricks: 1 x 2 = 2
Transport-type: tcp
Bricks:
Brick1: sto1.liris.cnrs.fr:/glusterfs/home/data
Brick2: sto2.liris.cnrs.fr:/glusterfs/home/data
Options Reconfigured:
performance.quick-read: on
cluster.metadata-self-heal: on
cluster.data-self-heal: on
cluster.entry-self-heal: on
cluster.consistent-metadata: true
auth.ssl-allow:
sto1.liris.cnrs.fr,sto2.liris.cnrs.fr,connect.liris.cnrs.fr
server.ssl: off
client.ssl: off
diagnostics.latency-measurement: off
diagnostics.count-fop-hits: off
BTW a first-repsonding option can be nice but is not exaclty the
same thing as under heavy load from one server you could fall onto
the other one. Our purpose is really to reduce bandwidth beetween
buildings when possible, not to use the faster server :)
--
Y.
-Krutika
From: "Yannick
Perret" <yannick.perret@xxxxxxxxxxxxx>
To: "Saravanakumar Arumugam"
<sarumuga@xxxxxxxxxx>, gluster-users@xxxxxxxxxxx
Sent: Friday, March 4, 2016 2:43:16 PM
Subject: Re: Per-client prefered
server?
Le 03/03/2016 15:17,
Saravanakumar Arumugam a écrit :
On 03/03/2016 05:38 PM, Yannick
Perret wrote:
Hello,
I can't find if it is possible to set a prefered server on
a per-client basis for replica volumes, so I ask the
question here.
The context: we have 2 storage servers, each in one
building. We also have several virtual machines on each
building, and they can migrate from one building to an
other (depending on load, maintenance…).
So (for testing at this time) I setup a x2 replica volume,
one replica on each storage server of course. As most of
our volumes are "many reads - few writes" it would be
better for bandwidth that each client uses the "nearest"
storage server (local building switch) - for reading, of
course. The 2 buildings have a good netlink but we prefer
to minimize - when not needed - data transferts beetween
them (this link is shared).
Can you see a solution for this kind of tuning? As far as
I understand geo-replica is not really what I need, no?
Yes, geo-replication "cannot" be used as you wish to carry
out "write" operation on Slave side.
Ok, thanks. I was pretty sure it was the case but I prefer to
ask.
It exists "cluster.read-subvolume" option of course but we
can have clients on both building so a per-volume option
is not what we need. An per-client equivalent of this
option should be nice.
I tested by myself a small patch to perform this - and it
seems to work fine as far as I can see - but 1. before
continuing in this way I would first check if it exists an
other way and 2. I'm not familiar with the whole code so
I'm not sure that my tests are in the "state-of-the-art"
for glusterfs.
maybe you should share that interesting patch :) and get
better feedback about your test case.
My "patch" is quite simple: I added in
afr_read_subvol_select_by_policy()
(xlators/cluster/afr/src/afr-common.c) a target selection
similar to the one managed by "read_child" configuration (see
patches at the end).
Of course I also added the definition of this "forced_child"
in afr.h, in the same way favorite_child or read_child is
defined.
My real problem here is how to tell to client to change its
"forced-child" value.
I did this by reading it from a local file
(/var/lib/glusterd/forced-child) in init() and reconfigure()
(from xlators/cluster/afr/src/afr.c). This is fine at startup,
and when volume configuration changed, but I find the sending
a SIGUP is not enough because client detects that no change
occurs and do not call "reconfigure()". So for my tests I
modified glusterfsd/src/glusterfsd-mgmt.c so that if
/var/lib/glusterf/forced-child exists it behave as if a
configuration change occured (and so calls reconfigure() which
reload the forced-child value).
At this point it works as I expected but I think it is
possible to handle a new forced-child value without calling
all reconfigure().
Moreover this file contains a raw number, it would be better
to use a server name, which would be converted into index
after that.
If possible it may be better to send the new value using
'gluster' command on client? I.e. something like 'gluster
volume set client.prefered-server SERVER-NAME'?
Any advices welcome.
Regards,
--
Y.
<<<
--- glusterfs-3.6.7/xlators/cluster/afr/src/afr-common.c
2015-11-25 12:55:58.000000000 +0100
+++ glusterfs-3.6.7b/xlators/cluster/afr/src/afr-common.c
2015-12-10 14:59:18.898580772 +0100
@@ -764,10 +764,18 @@
int i = 0;
int read_subvol = -1;
afr_private_t *priv = NULL;
- afr_read_subvol_args_t local_args = {0,};
+ afr_read_subvol_args_t local_args = {0,};
priv = this->private;
+
+ /* if forced-child use it */
+ if ((priv->forced_child >= 0)
+ && (priv->forced_child <
priv->child_count)
+ && (readable[priv->forced_child])) {
+ return priv->forced_child;
+ }
+
/* first preference - explicitly specified or local
subvolume */
if (priv->read_child >= 0 &&
readable[priv->read_child])
return priv->read_child;
>>>
<<<
@@ -83,6 +83,7 @@
unsigned int hash_mode; /* for when read_child
is not set */
int favorite_child; /* subvolume to be preferred in
resolving
split-brain cases */
+ int forced_child; /* child to use (if possible) */
gf_boolean_t inodelk_trace;
gf_boolean_t entrylk_trace;
>>>
<<<
--- glusterfs-3.6.7/xlators/cluster/afr/src/afr.c
2015-11-25 12:55:58.000000000 +0100
+++ glusterfs-3.6.7b/xlators/cluster/afr/src/afr.c
2015-12-10 16:34:55.530790442 +0100
@@ -23,6 +23,7 @@
struct volume_options options[];
+
int32_t
notify (xlator_t *this, int32_t event,
void *data, ...)
@@ -106,9 +107,26 @@
int ret = -1;
int index = -1;
char *qtype = NULL;
+ FILE *prefer = NULL;
+ int i = -1;
priv = this->private;
+ /* if /var/lib/glusterd/forced-child exists read the
content
+ and use it as prefered target for read */
+ priv->forced_child = -1;
+ prefer = fopen("/var/lib/glusterd/forced-child",
"r");
+ if (prefer) {
+ if (fscanf(prefer, "%d", &i) == 1) {
+ if ((i >= 0) && (i <
priv->child_count)) {
+ priv->forced_child = i;
+ gf_log (this->name, GF_LOG_INFO,
+ "using %d as forced-child", i);
+ }
+ }
+ fclose(prefer);
+ }
+
GF_OPTION_RECONF ("afr-dirty-xattr",
priv->afr_dirty, options, str,
out);
@@ -234,6 +252,7 @@
int read_subvol_index = -1;
xlator_t *fav_child = NULL;
char *qtype = NULL;
+ FILE *prefer = NULL;
if (!this->children) {
gf_log (this->name, GF_LOG_ERROR,
@@ -261,6 +280,21 @@
priv->read_child = -1;
+ /* if /var/lib/glusterd/forced-child exists read the
content
+ and use it as prefered target for read */
+ priv->forced_child = -1;
+ prefer = fopen("/var/lib/glusterd/forced-child",
"r");
+ if (prefer) {
+ if (fscanf(prefer, "%d", &i) == 1) {
+ if ((i >= 0) && (i <
priv->child_count)) {
+ priv->forced_child = i;
+ gf_log (this->name, GF_LOG_INFO,
+ "using %d as
forced-child", i);
+ }
+ }
+ fclose(prefer);
+ }
+
GF_OPTION_INIT ("afr-dirty-xattr", priv->afr_dirty,
str, out);
GF_OPTION_INIT ("metadata-splitbrain-forced-heal",
>>>
<<<
--- glusterfs-3.6.7/glusterfsd/src/glusterfsd-mgmt.c
2015-11-25 12:55:58.000000000 +0100
+++ glusterfs-3.6.7b/glusterfsd/src/glusterfsd-mgmt.c
2015-12-10 16:34:20.530789162 +0100
@@ -1502,7 +1502,9 @@
if (size == oldvollen && (memcmp (oldvolfile,
rsp.spec, size) == 0)) {
gf_log (frame->this->name, GF_LOG_INFO,
"No change in volfile, continuing");
- goto out;
+ if (access("/var/lib/glusterd/forced-child", R_OK) !=
0) {
+ goto out; /* don't skip if exists to
re-read forced-child */
+ }
}
tmpfp = tmpfile ();
>>>
--
Y.
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