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From 8217d00a0a54457961e7ec7d3afb24e953923c7d Mon Sep 17 00:00:00 2001
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From: Ashish Pandey <aspandey@redhat.com>
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Date: Tue, 13 Mar 2018 14:03:20 +0530
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Subject: [PATCH 198/201] cluster/ec: Change default read policy to gfid-hash
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Problem:
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Whenever we read data from file over NFS, NFS reads
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more data then requested and caches it. Based on the
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stat information it makes sure that the cached/pre-read
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data is valid or not.
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Consider 4 + 2 EC volume and all the bricks are on
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differnt nodes.
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In EC, with round-robin read policy, reads are sent on
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different set of data bricks. This way, it balances the
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read fops to go on all the bricks and avoid heating UP
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(overloading) same set of bricks.
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Due to small difference in clock speed, it is possible
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that we get minor difference for atime, mtime or ctime
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for different bricks. That might cause a different stat
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returned to NFS based on which NFS will discard
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cached/pre-read data which is actually not changed and
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could be used.
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Solution:
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Change read policy for EC as gfid-hash. That will force
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all the read to go to same set of bricks.
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>Change-Id: I825441cc519e94bf3dc3aa0bd4cb7c6ae6392c84
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>BUG: 1554743
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>Signed-off-by: Ashish Pandey <aspandey@redhat.com>
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upstream patch: https://review.gluster.org/#/c/19703/
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Change-Id: I43e95717980ca52c228fdcb7863c58bd4d14151c
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BUG: 1559084
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Signed-off-by: Ashish Pandey <aspandey@redhat.com>
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Reviewed-on: https://code.engineering.redhat.com/gerrit/133746
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Tested-by: RHGS Build Bot <nigelb@redhat.com>
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Reviewed-by: Sunil Kumar Heggodu Gopala Acharya <sheggodu@redhat.com>
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---
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tests/basic/ec/ec-read-policy.t | 7 +++----
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xlators/cluster/ec/src/ec.c | 2 +-
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2 files changed, 4 insertions(+), 5 deletions(-)
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diff --git a/tests/basic/ec/ec-read-policy.t b/tests/basic/ec/ec-read-policy.t
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index e4390aa..fe6fe65 100644
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--- a/tests/basic/ec/ec-read-policy.t
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+++ b/tests/basic/ec/ec-read-policy.t
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@@ -20,10 +20,9 @@ TEST $CLI volume start $V0
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TEST glusterfs --direct-io-mode=yes --entry-timeout=0 --attribute-timeout=0 -s $H0 --volfile-id $V0 $M0
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EXPECT_WITHIN $CHILD_UP_TIMEOUT "6" ec_child_up_count $V0 0
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#TEST volume operations work fine
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-EXPECT "round-robin" mount_get_option_value $M0 $V0-disperse-0 read-policy
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-TEST $CLI volume set $V0 disperse.read-policy gfid-hash
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-EXPECT_WITHIN $CONFIG_UPDATE_TIMEOUT "gfid-hash" mount_get_option_value $M0 $V0-disperse-0 read-policy
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-TEST $CLI volume reset $V0 disperse.read-policy
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+
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+EXPECT "gfid-hash" mount_get_option_value $M0 $V0-disperse-0 read-policy
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+TEST $CLI volume set $V0 disperse.read-policy round-robin
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EXPECT_WITHIN $CONFIG_UPDATE_TIMEOUT "round-robin" mount_get_option_value $M0 $V0-disperse-0 read-policy
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#TEST if the option gives the intended behavior. The way we perform this test
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diff --git a/xlators/cluster/ec/src/ec.c b/xlators/cluster/ec/src/ec.c
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index 13ce7fb..bfdca64 100644
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--- a/xlators/cluster/ec/src/ec.c
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+++ b/xlators/cluster/ec/src/ec.c
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@@ -1447,7 +1447,7 @@ struct volume_options options[] =
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{ .key = {"read-policy" },
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.type = GF_OPTION_TYPE_STR,
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.value = {"round-robin", "gfid-hash"},
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- .default_value = "round-robin",
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+ .default_value = "gfid-hash",
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.description = "inode-read fops happen only on 'k' number of bricks in"
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" n=k+m disperse subvolume. 'round-robin' selects the read"
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" subvolume using round-robin algo. 'gfid-hash' selects read"
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--
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1.8.3.1
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