[Bugs] [Bug 1084508] read-ahead not working if open-behind is turned on

[bugzilla at redhat.com]

https://bugzilla.redhat.com/show_bug.cgi?id=1084508

Raghavendra G <rgowdapp at redhat.com> changed:

           What    |Removed                     |Added
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              Flags|                            |needinfo?(pgurusid at redhat.c
                   |                            |om)



--- Comment #3 from Raghavendra G <rgowdapp at redhat.com> ---
I think the issue is because of open-behind using anonymous-fd. See the
following option in open-behind:

        { .key  = {"read-after-open"},
          .type = GF_OPTION_TYPE_BOOL,
          .default_value = "no",
      .description = "read is sent only after actual open happens and real "
          "fd is obtained, instead of doing on anonymous fd (similar to
write)",
        },

The read-ahead cache is per-fd and stored in the context of fd. If open-behind
is using anonymous fds for doing reads, read is never sent on the fd which
read-ahead has seen (during open from application). So, there is no read-ahead
cache.

Can you retry the tests by setting option "read-after-open" in open-behind to
"yes"?

[root at unused glusterfs]# gluster volume set dist-rep
performance.read-after-open on
volume set: success
[root at unused glusterfs]# gluster volume info

Volume Name: dist-rep
Type: Distributed-Replicate
Volume ID: 201492ff-9eb8-48f9-a647-59b89853e3d3
Status: Created
Number of Bricks: 2 x 2 = 4
Transport-type: tcp
Bricks:
Brick1: booradley:/home/export-2/dist-rep1
Brick2: booradley:/home/export-2/dist-rep2
Brick3: booradley:/home/export-2/dist-rep3
Brick4: booradley:/home/export-2/dist-rep4
Options Reconfigured:
performance.read-after-open: on
performance.readdir-ahead: on

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