We’re dealing with a strange definition of “safe” here – but that would be the intention.  For tablets that have assigned wals that it cannot recover and you just want to move on, then deleting those entries will get those tablets to stop trying to recover the info and move on.


You could check to see if the referenced files exist and if they have any size – that would give you an idea of what magnitude of loss you will be dealing with.


One everything is back, you may want to consider a full compaction as a verification and root out any other issues.


Ed Coleman


From: Dickson, Matt MR [mailto:matt.dickson@defence.gov.au]
Sent: Monday, December 16, 2019 10:31 PM
To: user@accumulo.apache.org



So when scanning the metadata table I get a bunch of rows. One has a column family of log:…..  and this one references the wal’s.  There are actually two rows with separate wal’s listed. 


4d4;blah  log:host_1:997/hdfs//…/accumulo/wal/…/111111111111111   []   hdfs://…/accumulo/….

4d4;blah  log:host_1:997/hdfs//…/accumulo/wal/…/222222222222222   []   hdfs://…/accumulo/….


Is it safe to remove both of these rows?  


Looking at other ‘good’ tablets they have no wal row.


From: Ed Coleman <dev1@etcoleman.com>
Sent: Tuesday, 17 December 2019 1:53 PM
To: user@accumulo.apache.org


This is off the top of my head and I don’t have a local instance running to try anything to see if that would knock a few brains cells into recalling… so.


You don’t say what version, but there used to be an issue that if multiple tservers operated on a walog, the failed entry would cause the others to also fail.  You might be able to remove the hdfs://system/accumulo/recovery/434adfsdf124312f and the system will retry.


The other ways – as long as you really don’t care what may be in the wal logs.


Most certain, but also needs to be carefully done is to remove the wal references in the metadata table.  One way, it to use the shell and scan the metadata table for the tablet id range and pipe it to a file.  The with grep / awk, select the wal entries and the turn them into a deleterow command – one catch is the printed version of the row id is like id…col_fam:col_qual – and the delete command does not like the : (or it’s the other way round…)  And you may need to grand delete privileges to the metadata table…


scan -t accumulo.metadata -b 4d4; -e 4d4~ -np


The other way would be to identify the “missing” files and put an empty file into hdfs into its place.


Or, if you can take the table offline, then you can stash current files and then create a new table and bulk import it (set the splits, or do it in batches) Not sure if delete works on offline tables – that’s one thing to try first.


Ed Coleman


From: Dickson, Matt MR [mailto:matt.dickson@defence.gov.au]
Sent: Monday, December 16, 2019 8:53 PM
To: user@accumulo.apache.org



A correction to my description:


Looking at the Accumulo gui on the ‘Table Problems’ section there are 8K errors stating:


Table                     Problem Type                    Server                   Time                      Resource                             Exception

Table                     TABLET_LOAD                   host                       datetime              resourceUUID                    java.io.IOException: ….FileNoteFoundException: File does not exist: hdfs://system/accumulo/recovery/434adfsdf124312f/failed/data


These seem to correspond to records in the accumulo.metadata table:


Scan –t accumulo.metadata –b ~err


~err_zxn  TABLET_LOAD: …………


From: Dickson, Matt MR <matt.dickson@defence.gov.au>
Sent: Tuesday, 17 December 2019 12:29 PM
To: user@accumulo.apache.org






I’m trying to recover from an issue that was caused by the table.split.threshold being set to a very low size that then generated a massive load on zookeeper and cluster nodes timing out communicating with zookeeper while Accumulo was splitting tablets.  This was noticed when tablet servers were being declared dead.


I’ve corrected the threshold and Accumulo is back online however there are 8K unhosted tablets that are not coming online. 


Running check the checkTablets script produces the exact number of errors as there are unhosted tablets with a message like:


4d4;blah::words::4gfv43@(host:9997[23423442344234f23fd],null,null_ is ASSIGNED_TO_DEAD_SERVER #walogs:2


I’m not concerned if there is data in these tablets and it is lost in returning the system to a healthy state because I suspect other Accumulo operations can’t proceed while tablets are unhosted so just need to remove these issues.


Any advice would be great.


Thanks in advance,