BookKeeper Getting Started Guide
Programming with BookKeeper
Instantiating BookKeeper.
The first step to use BookKeeper is to instantiate a BookKeeper object:
org.apache.bookkeeper.BookKeeper
There are three BookKeeper constructors:
public BookKeeper(String servers) throws KeeperException, IOException
where:
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servers is a comma-separated list of ZooKeeper servers.
public BookKeeper(ZooKeeper zk) throws InterruptedException, KeeperException
where:
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zk is a ZooKeeper object. This constructor is useful when the application also using ZooKeeper and wants to have a single instance of ZooKeeper.
public BookKeeper(ZooKeeper zk, ClientSocketChannelFactory channelFactory) throws InterruptedException, KeeperException
where:
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zk is a ZooKeeper object. This constructor is useful when the application also using ZooKeeper and wants to have a single instance of ZooKeeper.
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channelFactory is a netty channel object (org.jboss.netty.channel.socket).
Creating a ledger.
Before writing entries to BookKeeper, it is necessary to create a ledger. With the current BookKeeper API, it is possible to create a ledger both synchronously or asynchronously. The following methods belong to org.apache.bookkeeper.client.BookKeeper.
Synchronous call:
public LedgerHandle createLedger(int ensSize, int qSize, DigestType type, byte passwd[]) throws KeeperException, InterruptedException, IOException, BKException
where:
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ensSize is the number of bookies (ensemble size);
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qSize is the write quorum size;
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type is the type of digest used with entries: either MAC or CRC32.
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passwd is a password that authorizes the client to write to the ledger being created.
All further operations on a ledger are invoked through the LedgerHandle object returned.
As a convenience, we provide a createLedger with default parameters (3,2,VERIFIABLE), and the only two input parameters it requires are a digest type and a password.
Asynchronous call:
public void asyncCreateLedger(int ensSize, int qSize, DigestType type, byte passwd[], CreateCallback cb, Object ctx )
The parameters are the same of the synchronous version, with the exception of cb and ctx. CreateCallback is an interface in org.apache.bookkeeper.client.AsyncCallback, and a class implementing it has to implement a method called createComplete that has the following signature:
void createComplete(int rc, LedgerHandle lh, Object ctx);
where:
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rc is a return code (please refer to org.apache.bookeeper.client.BKException for a list);
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lh is a LedgerHandle object to manipulate a ledger;
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ctx is a control object for accountability purposes. It can be essentially any object the application is happy with.
The ctx object passed as a parameter to the call to create a ledger is the one same returned in the callback.
Adding entries to a ledger.
Once we have a ledger handle lh obtained through a call to create a ledger, we can start writing entries. As with creating ledgers, we can write both synchronously and asynchronously. The following methods belong to org.apache.bookkeeper.client.LedgerHandle.
Synchronous call:
public long addEntry(byte[] data) throws InterruptedException
where:
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data is a byte array;
A call to addEntry returns the status of the operation (please refer to org.apache.bookeeper.client.BKDefs for a list);
Asynchronous call:
public void asyncAddEntry(byte[] data, AddCallback cb, Object ctx)
It also takes a byte array as the sequence of bytes to be stored as an entry. Additionaly, it takes a callback object cb and a control object ctx. The callback object must implement the AddCallback interface in org.apache.bookkeeper.client.AsyncCallback, and a class implementing it has to implement a method called addComplete that has the following signature:
void addComplete(int rc, LedgerHandle lh, long entryId, Object ctx);
where:
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rc is a return code (please refer to org.apache.bookeeper.client.BKDefs for a list);
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lh is a LedgerHandle object to manipulate a ledger;
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entryId is the identifier of entry associated with this request;
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ctx is control object used for accountability purposes. It can be any object the application is happy with.
Closing a ledger.
Once a client is done writing, it closes the ledger. The following methods belong to org.apache.bookkeeper.client.LedgerHandle.
Synchronous close:
public void close() throws InterruptedException
It takes no input parameters.
Asynchronous close:
public void asyncClose(CloseCallback cb, Object ctx) throws InterruptedException
It takes a callback object cb and a control object ctx. The callback object must implement the CloseCallback interface in org.apache.bookkeeper.client.AsyncCallback, and a class implementing it has to implement a method called closeComplete that has the following signature:
void closeComplete(int rc, LedgerHandle lh, Object ctx)
where:
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rc is a return code (please refer to org.apache.bookeeper.client.BKDefs for a list);
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lh is a LedgerHandle object to manipulate a ledger;
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ctx is control object used for accountability purposes.
Opening a ledger.
To read from a ledger, a client must open it first. The following methods belong to org.apache.bookkeeper.client.BookKeeper.
Synchronous open:
public LedgerHandle openLedger(long lId, DigestType type, byte passwd[]) throws InterruptedException, BKException
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ledgerId is the ledger identifier;
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type is the type of digest used with entries: either MAC or CRC32.
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passwd is a password to access the ledger (used only in the case of VERIFIABLE ledgers);
Asynchronous open:
public void asyncOpenLedger(long lId, DigestType type, byte passwd[], OpenCallback cb, Object ctx)
It also takes a a ledger identifier and a password. Additionaly, it takes a callback object cb and a control object ctx. The callback object must implement the OpenCallback interface in org.apache.bookkeeper.client.AsyncCallback, and a class implementing it has to implement a method called openComplete that has the following signature:
public void openComplete(int rc, LedgerHandle lh, Object ctx)
where:
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rc is a return code (please refer to org.apache.bookeeper.client.BKDefs for a list);
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lh is a LedgerHandle object to manipulate a ledger;
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ctx is control object used for accountability purposes.
Reading from ledger
Read calls may request one or more consecutive entries. The following methods belong to org.apache.bookkeeper.client.LedgerHandle.
Synchronous read:
public Enumeration<LedgerEntry> readEntries(long firstEntry, long lastEntry) throws InterruptedException, BKException
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firstEntry is the identifier of the first entry in the sequence of entries to read;
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lastEntry is the identifier of the last entry in the sequence of entries to read.
Asynchronous read:
public void asyncReadEntries(long firstEntry, long lastEntry, ReadCallback cb, Object ctx) throws BKException, InterruptedException
It also takes a first and a last entry identifiers. Additionaly, it takes a callback object cb and a control object ctx. The callback object must implement the ReadCallback interface in org.apache.bookkeeper.client.AsyncCallback, and a class implementing it has to implement a method called readComplete that has the following signature:
void readComplete(int rc, LedgerHandle lh, Enumeration<LedgerEntry> seq, Object ctx)
where:
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rc is a return code (please refer to org.apache.bookeeper.client.BKDefs for a list);
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lh is a LedgerHandle object to manipulate a ledger;
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seq is a Enumeration<LedgerEntry> object to containing the list of entries requested;
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ctx is control object used for accountability purposes.
Deleting a ledger
Once a client is done with a ledger and is sure that nobody will ever need to read from it again, they can delete the ledger. The following methods belong to org.apache.bookkeeper.client.BookKeeper.
Synchronous delete:
public void deleteLedger(long lId) throws InterruptedException, BKException
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lId is the ledger identifier;
Asynchronous delete:
public void asyncDeleteLedger(long lId, DeleteCallback cb, Object ctx)
It takes a ledger identifier. Additionally, it takes a callback object cb and a control object ctx. The callback object must implement the DeleteCallback interface in org.apache.bookkeeper.client.AsyncCallback, and a class implementing it has to implement a method called deleteComplete that has the following signature:
void deleteComplete(int rc, Object ctx)
where:
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rc is a return code (please refer to org.apache.bookeeper.client.BKDefs for a list);
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ctx is control object used for accountability purposes.