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cluster/ec: Change default read policy to gfid-hash

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Problem:
Whenever we read data from file over NFS, NFS reads
more data then requested and caches it. Based on the
stat information it makes sure that the cached/pre-read
data is valid or not.

Consider 4 + 2 EC volume and all the bricks are on
differnt nodes.

In EC, with round-robin read policy, reads are sent on
different set of data bricks. This way, it balances the
read fops to go on all the bricks and avoid heating UP
(overloading) same set of bricks.

Due to small difference in clock speed, it is possible
that we get minor difference for atime, mtime or ctime
for different bricks. That might cause a different stat
returned to NFS based on which NFS will discard
cached/pre-read data which is actually not changed and
could be used.

Solution:
Change read policy for EC as gfid-hash. That will force
all the read to go to same set of bricks.

Change-Id: I825441cc519e94bf3dc3aa0bd4cb7c6ae6392c84
BUG: 1554743
Signed-off-by: Ashish Pandey <aspandey@redhat.com>
This commit is contained in:
Ashish Pandey 2018-03-13 14:03:20 +05:30
parent a4e34af38d
commit f32f85c4e6
2 changed files with 4 additions and 5 deletions
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7
tests/basic/ec/ec-read-policy.t
View File

@ -20,10 +20,9 @@ TEST $CLI volume start $V0
TEST glusterfs --direct-io-mode=yes --entry-timeout=0 --attribute-timeout=0 -s $H0 --volfile-id $V0 $M0
EXPECT_WITHIN $CHILD_UP_TIMEOUT "6" ec_child_up_count $V0 0
#TEST volume operations work fine
EXPECT "round-robin" mount_get_option_value $M0 $V0-disperse-0 read-policy
TEST $CLI volume set $V0 disperse.read-policy gfid-hash
EXPECT_WITHIN $CONFIG_UPDATE_TIMEOUT "gfid-hash" mount_get_option_value $M0 $V0-disperse-0 read-policy
TEST $CLI volume reset $V0 disperse.read-policy
EXPECT "gfid-hash" mount_get_option_value $M0 $V0-disperse-0 read-policy
TEST $CLI volume set $V0 disperse.read-policy round-robin
EXPECT_WITHIN $CONFIG_UPDATE_TIMEOUT "round-robin" mount_get_option_value $M0 $V0-disperse-0 read-policy
#TEST if the option gives the intended behavior. The way we perform this test

2
xlators/cluster/ec/src/ec.c
View File

@ -1580,7 +1580,7 @@ struct volume_options options[] =
{ .key = {"read-policy" },
.type = GF_OPTION_TYPE_STR,
.value = {"round-robin", "gfid-hash"},
.default_value = "round-robin",
.default_value = "gfid-hash",
.op_version = {GD_OP_VERSION_3_7_6},
.flags = OPT_FLAG_SETTABLE | OPT_FLAG_CLIENT_OPT | OPT_FLAG_DOC,
.tags = {"disperse"},