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  1. Couchbase Server
  2. MB-41255

Value eviction bucket - Replication of deletes with XATTRS will fail if return EWOULD_BLOCK

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    • Triaged
    • 1
    • Yes

    Description

      Problem

      As described in CBSE-8828, for a replica DCP stream. If a previous item that uses XATTRs is to be deleted, however it is not resident - then we must perform a bgfetch - see MB-36087. When the bgfetch is complete we replay PassiveStream::messageReceived. However this time it fails because the last seqno now equals the sequence number of the deletion and so it is discarded.

      Suggested Possible Solution

      • only set the last seqno to the seqno of the message just received, once the message has been completed or
      • If an EWOULD_BLOCK occurs reserve the setting of the last seqno so the message can be received again.

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        Issue Links

          backports to

          Technical task - A technical task. MB-41387 [BP] MB-41255 to 6.0.4 - MP2

          • Critical - Crashes, loss of data, severe memory leak.
          • Resolved
          blocks

          Task - A task that needs to be done. MB-41310 6.0.4-MP2

          • Major - Major loss of function.
          • Resolved
          is caused by

          Bug - A problem which impairs or prevents the functions of the product. MB-36087 DeleteWithMeta against a value evicted xattr document crashes memcached

          • Critical - Crashes, loss of data, severe memory leak.
          • Closed
          relates to

          Bug - A problem which impairs or prevents the functions of the product. MB-41471 Upgrading to MB-41255

          • Critical - Crashes, loss of data, severe memory leak.
          • Resolved
          mentioned in

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          Activity

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            shivani.gupta Shivani Gupta added a comment -

            Thanks Dave Rigby.

            Depends on how you define "regression" . I believe the issue was introduced with XATTR support; when replicating deletes to items which previously had XATTRs in them. To hit this issue you need to be using XATTRs, which were new in 5.0.0 - so while it's true we didn't encounter this issue prior to v5, you also need to be using the new v5 feature to hit it.

            Customer was upgrading from 6.0 to 6.6. Given that the fix was backported to 6.0.5 also, looks like the issue existed in 6.0.x as well. Likely that the customer was not using XATTRs and their previous upgrades (to 6.0.x) were hence not impacted. So yes, probably not a regression.

            shivani.gupta Shivani Gupta added a comment - Thanks Dave Rigby . Depends on how you define "regression"  . I believe the issue was introduced with XATTR support; when replicating deletes to items which previously had XATTRs in them. To hit this issue you need to be using XATTRs, which were new in 5.0.0 - so while it's true we didn't encounter this issue prior to v5, you also need to be using the new v5 feature to hit it. Customer was upgrading from 6.0 to 6.6. Given that the fix was backported to 6.0.5 also, looks like the issue existed in 6.0.x as well. Likely that the customer was not using XATTRs and their previous upgrades (to 6.0.x) were hence not impacted. So yes, probably not a regression.
            build-team Couchbase Build Team added a comment -

            Build couchbase-server-7.0.0-4255 contains kv_engine commit 5958386 with commit message:
            [BP] MB-41255: Don't bgfetch for a replica delete of an xattr

            build-team Couchbase Build Team added a comment - Build couchbase-server-7.0.0-4255 contains kv_engine commit 5958386 with commit message: [BP] MB-41255 : Don't bgfetch for a replica delete of an xattr
            build-team Couchbase Build Team added a comment -

            Build couchbase-server-7.0.0-4255 contains kv_engine commit d88694a with commit message:
            MB-41255: Merge branch '6.5.2' into mad-hatter

            build-team Couchbase Build Team added a comment - Build couchbase-server-7.0.0-4255 contains kv_engine commit d88694a with commit message: MB-41255 : Merge branch '6.5.2' into mad-hatter
            build-team Couchbase Build Team added a comment -

            Build couchbase-server-7.0.0-4255 contains kv_engine commit c690fba with commit message:
            Merge "MB-41255: Merge branch '6.5.2' into mad-hatter" into mad-hatter

            build-team Couchbase Build Team added a comment - Build couchbase-server-7.0.0-4255 contains kv_engine commit c690fba with commit message: Merge " MB-41255 : Merge branch '6.5.2' into mad-hatter" into mad-hatter
            build-team Couchbase Build Team added a comment -

            Build couchbase-server-6.6.2-9411 contains kv_engine commit 5958386 with commit message:
            [BP] MB-41255: Don't bgfetch for a replica delete of an xattr

            build-team Couchbase Build Team added a comment - Build couchbase-server-6.6.2-9411 contains kv_engine commit 5958386 with commit message: [BP] MB-41255 : Don't bgfetch for a replica delete of an xattr
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            People

              ashwin.govindarajulu Ashwin Govindarajulu
              owend Daniel Owen
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              Dates

                Created:
                Updated:
                Resolved:

                PagerDuty