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https://issues.apache.org/jira/browse/ZOOKEEPER-712?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Erwin Tam updated ZOOKEEPER-712:
Status: Patch Available (was: Open)
First pass at implementing bookie recovery as an admin tool. The patch
uploaded has two new files:
BookieRecoveryTest.java and BookKeeperTools.java (with a corresponding new
directory under bookkeeper/tools).
The main API that BookKeeperTools.java implements is the following:
public void asyncRecoverBookieData(final InetSocketAddress bookieSrc, final
InetSocketAddress bookieDest,
final RecoverCallback cb, final Object context);
The synchronous version of this API is here:
public void recoverBookieData(final InetSocketAddress bookieSrc, final
InetSocketAddress bookieDest)
throws InterruptedException;
This is to recover all of the bookie ledger data that was present on a dead
input bookieSrc. The other input 'bookieDest' is optional and if passed, we
will recover all data to that bookie server specifically. Otherwise for each
ledger being recovered that was stored on the bookieSrc, we choose one of the
other available bookie servers and re-replicate the ledger fragment entries to
there.
A command line way to invoke this is done via a main method in BookKeeperTools
which expects the following 2-3 input parameters.
USAGE: BookKeeperTools zkServers bookieSrc [bookieDest]
zkServers is a comma separated list of host:port pairs for the ZooKeeper
servers in the cluster.
bookieSrc is the host:port for the bookie server we are recovering data from.
bookieDest is the host:port (optional) for the bookie server we want to recover
the data to.
Current limitations: There is no way to know what each ledger's digest type or
key/password are. That metadata isn't stored anywhere we can access readily.
Thus for now, we are assuming that all ledgers to be recovered have been
created with the same digest type and password. These values are set via java
system properties called digestType and passwd. Once we have a way to
store and retrieve this information (via ZK most likely and stored by the
Bookie servers when new ledgers are created), we can modify this aspect of the
bookie recovery tool.
Pseudocode:
Inputs:
zkServers - Used to create a ZK client so we can read in all of the BK metadata
needed to perform the bookie recovery.
bookieSrc - Used to match against ledger metadata indicating which bookie
servers comprise the ensembles that make up a ledger.
bookieDest - Optionally used to write the recovered ledger data to directly.
1. Sync with ZK
2. Read from ZK to get all available bookie servers (only if bookieDest was not
passed).
3. Read from ZK to get all active ledgers.
4. For each ledger, open it to obtain the LedgerHandle.
5. For each ledger fragment, see if the dead input bookieSrc is a part of the
ensemble for it.
6. For each ledger fragment that needs to be recovered, find the entries that
were actually stored on the bookieSrc. Since we stripe data across bookies in
the ensemble, not all ledger entries in the fragment would have been stored on
the bookieSrc.
7. For each of the ledger entries in the fragment that were stored on the
bookieSrc, use the BookKeeper client to read it. Using the client will take
care of choosing one of the other bookies where this data is available since
the bookieSrc server is dead.
8. Choosing a new bookieDest (either passed in explicitly or chosen at random
currently among the available bookie servers), write this ledger entry directly
to there using the BookieClient (the layer that talks to the bookie servers
directly).
9. Once all ledger entries for all fragments for a ledger have been recovered
and re-replicated, update ZK so the ledger's metadata now points to the new
bookie server where this data has been re-replicated to. We choose a single
new bookie for each ledger to store the recovered data.
Bookie recovery
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Key: ZOOKEEPER-712
URL: https://issues.apache.org/jira/browse/ZOOKEEPER-712
Project: Zookeeper
Issue Type: New Feature
Components: contrib-bookkeeper
Reporter: Flavio Paiva Junqueira
Assignee: Erwin Tam
Attachments: ZOOKEEPER-712.patch
Recover the ledger fragments of a bookie once it crashes.
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