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From "Dickson, Matt MR" <matt.dick...@defence.gov.au>
Subject RE: Fix "Table x has a hole" [SEC=UNOFFICIAL]
Date Wed, 01 Mar 2017 05:23:02 GMT
UNOFFICIAL

Thanks for that Keith,

That's got it working again.  As for the cause, I had an error in the logs stating a tablet
was hosted and assigned.  I've always removed the referenced tablet in the metadata table
to fix this and had no issues in the past.  It looks like I fat fingered the deletion which
removed the wrong entry so not an issue with Accumulo.

Thanks. 

-----Original Message-----
From: Keith Turner [mailto:keith@deenlo.com]
Sent: Wednesday, 1 March 2017 03:36
To: user@accumulo.apache.org
Subject: Re: Fix "Table x has a hole" [SEC=UNOFFICIAL]

Below are some commands that show how to recreate this problem and how
to fix it.   Each table in the metadata table has a pointer to the
previous tablets.  Adding and removing splits to a table changes this.

  root@uno> createtable test

Get the tables ID below we will need it later.

  root@uno test> tables -l
  accumulo.metadata    =>        !0
  accumulo.replication =>      +rep
  accumulo.root        =>        +r
  test                 =>         3
  trace                =>         1

Add some splits and then scan the metadata table.  The pointers to the previous tablet are
in the ~tab:~pr column.  The scan below uses the table id above.

  root@uno test> addsplits 11111111 3333333
  root@uno test> scan -t accumulo.metadata -c ~tab:~pr -b 3; -e 3<
  3;11111111 ~tab:~pr []    \x00
  3;3333333 ~tab:~pr []    \x0111111111
  3< ~tab:~pr []    \x013333333

Add another split and rescan the metadata table.

  root@uno test> addsplits 2222222
  root@uno test> scan -t accumulo.metadata -c ~tab:~pr -b 3; -e 3<
  3;11111111 ~tab:~pr []    \x00
  3;2222222 ~tab:~pr []    \x0111111111
  3;3333333 ~tab:~pr []    \x012222222
  3< ~tab:~pr []    \x013333333

Grant permission to write to the metadata table and then recreate the problem you have.

  root@uno test> grant Table.WRITE -u root -t accumulo.metadata
  root@uno test> table accumulo.metadata
  root@uno accumulo.metadata> insert 3;3333333 ~tab ~pr \x0111111111
  root@uno accumulo.metadata> scan -t accumulo.metadata -c ~tab:~pr -b 3; -e 3<
  3;11111111 ~tab:~pr []    \x00
  3;2222222 ~tab:~pr []    \x0111111111
  3;3333333 ~tab:~pr []    \x0111111111
  3< ~tab:~pr []    \x013333333

If you ran check for metadata problems here, should see the error message you saw.  Below,
the pointer is fixed and write permission is revoked (to prevent accidental writes in the
future).

  root@uno accumulo.metadata> insert 3;3333333 ~tab ~pr \x012222222
  root@uno accumulo.metadata> revoke Table.WRITE -u root -t accumulo.metadata
  root@uno accumulo.metadata>

After running the command above to fix the potiner, check for metadata problems should be
happy.

It would be nice to try to track down the cause of this.  Spliting a tablet involves three
metadata operations.  For fault tolerance, the columns ~tab:oldprevrow and ~tab:splitRatio
are temporarily written.
If a tablet server dies in the middle of splitting a tablet, then Accumulo will see these
temporary columns and attempt to continue the split.  So I am curious if you see these columns?

On Sun, Feb 26, 2017 at 6:49 PM, Dickson, Matt MR <matt.dickson@defence.gov.au> wrote:
> UNOFFICIAL
>
> Running the CheckForMetadataProblems on Accumulo is listing
>
> Table xxx has a hole 11111111 != 2222222
>
> Is there a correct way to repair this?
>
> Thanks in advance.

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