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 is one BookKeeper constructor:
public BookKeeper(String servers) throws KeeperException, IOException
where servers is a comma-separated list of ZooKeeper servers.
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, QMode mode, 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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mode is the ledger mode (QMode.GENERIC, QMode.VERIFIABLE). If mode is QMode.GENERIC, then ensSize has to be at least 3t+1, and qSize has to be 2t+1. t is the maximum number of tolerated bookie failures.
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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 input parameter it requires is a password.
Asynchronous call:
public void asyncCreateLedger(int ensSize, int qSize, QMode mode, byte passwd[], CreateCallback cb, Object ctx ) throws KeeperException, InterruptedException, IOException, BKException
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.BKDefs 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;
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) throws InterruptedException
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.
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 KeeperException, 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, byte passwd[]) throws KeeperException, InterruptedException, IOException, BKException
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ledgerId is the ledger identifier;
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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, byte passwd[], OpenCallback cb, Object ctx) throws InterruptedException
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 LedgerSequence 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, LedgerSequence 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 LedgerSequence object to containing the list of entries requested;
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ctx is control object used for accountability purposes.