; Thu, 3 Dec 2015 04:29:48 +0000 (UTC) Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit Subject: svn commit: r1717709 [28/43] - in /zookeeper/site/trunk: content/ content/doc/r3.4.7/ content/doc/r3.4.7/api/ content/doc/r3.4.7/api/org/ content/doc/r3.4.7/api/org/apache/ content/doc/r3.4.7/api/org/apache/zookeeper/ content/doc/r3.4.7/api/org/apache/... Date: Thu, 03 Dec 2015 04:29:45 -0000 To: commits@zookeeper.apache.org From: rgs@apache.org X-Mailer: svnmailer-1.0.9 Message-Id: <20151203042948.A33383A0D1C@svn01-us-west.apache.org> Added: zookeeper/site/trunk/content/doc/r3.4.7/bookkeeperOverview.html URL: http://svn.apache.org/viewvc/zookeeper/site/trunk/content/doc/r3.4.7/bookkeeperOverview.html?rev=1717709&view=auto ============================================================================== --- zookeeper/site/trunk/content/doc/r3.4.7/bookkeeperOverview.html (added) +++ zookeeper/site/trunk/content/doc/r3.4.7/bookkeeperOverview.html Thu Dec 3 04:29:41 2015 @@ -0,0 +1,694 @@ + + + + + + + +BookKeeper overview + + + + + + + + + +

+ +

+Apache > ZooKeeper > ZooKeeper +

+ + +

+ +

+ + +

+ +

+ + +

+ + + + + +

+ PDF +

BookKeeper overview

+BookKeeper overview +
- +BookKeeper introduction +
- +In slightly more detail... +
- +Bookkeeper elements and concepts +
- +Bookkeeper initial design +
- +Bookkeeper metadata management +
- +Closing out ledgers +
+

+ + + + + +

BookKeeper overview

+ +

BookKeeper introduction

+ BookKeeper is a replicated service to reliably log streams of records. In BookKeeper, + servers are "bookies", log streams are "ledgers", and each unit of a log (aka record) is a + "ledger entry". BookKeeper is designed to be reliable; bookies, the servers that store + ledgers, can crash, corrupt data, discard data, but as long as there are enough bookies + behaving correctly the service as a whole behaves correctly. +

+ The initial motivation for BookKeeper comes from the namenode of HDFS. Namenodes have to + log operations in a reliable fashion so that recovery is possible in the case of crashes. + We have found the applications for BookKeeper extend far beyond HDFS, however. Essentially, + any application that requires an append storage can replace their implementations with + BookKeeper. BookKeeper has the advantage of scaling throughput with the number of servers. +

+ At a high level, a bookkeeper client receives entries from a client application and stores it to + sets of bookies, and there are a few advantages in having such a service: +

+ +
+ We can use hardware that is optimized for such a service. We currently believe that such a + system has to be optimized only for disk I/O; +
+ +
+ +
+ We can have a pool of servers implementing such a log system, and shared among a number of servers; +
+ +
+ +
+ We can have a higher degree of replication with such a pool, which makes sense if the hardware necessary for it is cheaper compared to the one the application uses. +
+ +

+ +

In slightly more detail...

BookKeeper implements highly available logs, and it has been designed with write-ahead logging in mind. Besides high availability + due to the replicated nature of the service, it provides high throughput due to striping. As we write entries in a subset of bookies of an + ensemble and rotate writes across available quorums, we are able to increase throughput with the number of servers for both reads and writes. + Scalability is a property that is possible to achieve in this case due to the use of quorums. Other replication techniques, such as + state-machine replication, do not enable such a property. +

An application first creates a ledger before writing to bookies through a local BookKeeper client instance. + Upon creating a ledger, a BookKeeper client writes metadata about the ledger to ZooKeeper. Each ledger currently + has a single writer. This writer has to execute a close ledger operation before any other client can read from it. + If the writer of a ledger does not close a ledger properly because, for example, it has crashed before having the + opportunity of closing the ledger, then the next client that tries to open a ledger executes a procedure to recover + it. As closing a ledger consists essentially of writing the last entry written to a ledger to ZooKeeper, the recovery + procedure simply finds the last entry written correctly and writes it to ZooKeeper. +

+ Note that currently this recovery procedure is executed automatically upon trying to open a ledger and no explicit action is necessary. + Although two clients may try to recover a ledger concurrently, only one will succeed, the first one that is able to create the close znode + for the ledger. +

+ +

Bookkeeper elements and concepts

+ BookKeeper uses four basic elements: +

+ +
+ +Ledger: A ledger is a sequence of entries, and each entry is a sequence of bytes. Entries are + written sequentially to a ledger and at most once. Consequently, ledgers have an append-only semantics; +
+ +
+ +
+ +BookKeeper client: A client runs along with a BookKeeper application, and it enables applications + to execute operations on ledgers, such as creating a ledger and writing to it; +
+ +
+ +
+ +Bookie: A bookie is a BookKeeper storage server. Bookies store the content of ledgers. For any given + ledger L, we call an ensemble the group of bookies storing the content of L. For performance, we store on + each bookie of an ensemble only a fragment of a ledger. That is, we stripe when writing entries to a ledger such that + each entry is written to sub-group of bookies of the ensemble. +
+ +
+ +
+ +Metadata storage service: BookKeeper requires a metadata storage service to store information related + to ledgers and available bookies. We currently use ZooKeeper for such a task. +
+ +

+ +

Bookkeeper initial design

+ A set of bookies implements BookKeeper, and we use a quorum-based protocol to replicate data across the bookies. + There are basically two operations to an existing ledger: read and append. Here is the complete API list + (mode detail + here): +

+ +
+ Create ledger: creates a new empty ledger; +
+ +
+ +
+ Open ledger: opens an existing ledger for reading; +
+ +
+ +
+ Add entry: adds a record to a ledger either synchronously or asynchronously; +
+ +
+ +
+ Read entries: reads a sequence of entries from a ledger either synchronously or asynchronously +
+ +

+ There is only a single client that can write to a ledger. Once that ledger is closed or the client fails, + no more entries can be added. (We take advantage of this behavior to provide our strong guarantees.) + There will not be gaps in the ledger. Fingers get broken, people get roughed up or end up in prison when + books are manipulated, so there is no deleting or changing of entries. +

+ + + + + + + +

BookKeeper Overview

+ +

+ A simple use of BooKeeper is to implement a write-ahead transaction log. A server maintains an in-memory data structure + (with periodic snapshots for example) and logs changes to that structure before it applies the change. The application + server creates a ledger at startup and store the ledger id and password in a well known place (ZooKeeper maybe). When + it needs to make a change, the server adds an entry with the change information to a ledger and apply the change when + BookKeeper adds the entry successfully. The server can even use asyncAddEntry to queue up many changes for high change + throughput. BooKeeper meticulously logs the changes in order and call the completion functions in order. +

+ When the application server dies, a backup server will come online, get the last snapshot and then it will open the + ledger of the old server and read all the entries from the time the snapshot was taken. (Since it doesn't know the + last entry number it will use MAX_INTEGER). Once all the entries have been processed, it will close the ledger and + start a new one for its use. +

+ A client library takes care of communicating with bookies and managing entry numbers. An entry has the following fields: +

+ + +Entry fields + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + +

Entry fields
Field	Type	Description
Ledger number	long	The id of the ledger of this entry
Entry number	long	The id of this entry
last confirmed (LC)	long	id of the last recorded entry
data	byte[]	the entry data (supplied by application)
authentication code	byte[]	Message authentication code that includes all other fields of the entry

+ The client library generates a ledger entry. None of the fields are modified by the bookies and only the first three + fields are interpreted by the bookies. +

+ To add to a ledger, the client generates the entry above using the ledger number. The entry number will be one more + than the last entry generated. The LC field contains the last entry that has been successfully recorded by BookKeeper. + If the client writes entries one at a time, LC is the last entry id. But, if the client is using asyncAddEntry, there + may be many entries in flight. An entry is considered recorded when both of the following conditions are met: +

+ +
+ the entry has been accepted by a quorum of bookies +
+ +
+ +
+ all entries with a lower entry id have been accepted by a quorum of bookies +
+ +

+ +LC seems mysterious right now, but it is too early to explain how we use it; just smile and move on. +

+ Once all the other fields have been field in, the client generates an authentication code with all of the previous fields. + The entry is then sent to a quorum of bookies to be recorded. Any failures will result in the entry being sent to a new + quorum of bookies. +

+ To read, the client library initially contacts a bookie and starts requesting entries. If an entry is missing or + invalid (a bad MAC for example), the client will make a request to a different bookie. By using quorum writes, + as long as enough bookies are up we are guaranteed to eventually be able to read an entry. +

+ +

Bookkeeper metadata management

+ There are some meta data that needs to be made available to BookKeeper clients: +

+ +
+ The available bookies; +
+ +
+ +
+ The list of ledgers; +
+ +
+ +
+ The list of bookies that have been used for a given ledger; +
+ +
+ +
+ The last entry of a ledger; +
+ +

+ We maintain this information in ZooKeeper. Bookies use ephemeral nodes to indicate their availability. Clients + use znodes to track ledger creation and deletion and also to know the end of the ledger and the bookies that + were used to store the ledger. Bookies also watch the ledger list so that they can cleanup ledgers that get deleted. +

+ +

Closing out ledgers

+ The process of closing out the ledger and finding the last ledger is difficult due to the durability guarantees of BookKeeper: +

+ +
+ If an entry has been successfully recorded, it must be readable. +
+ +
+ +
+ If an entry is read once, it must always be available to be read. +
+ +

+ If the ledger was closed gracefully, ZooKeeper will have the last entry and everything will work well. But, if the + BookKeeper client that was writing the ledger dies, there is some recovery that needs to take place. +

+ The problematic entries are the ones at the end of the ledger. There can be entries in flight when a BookKeeper client + dies. If the entry only gets to one bookie, the entry should not be readable since the entry will disappear if that bookie + fails. If the entry is only on one bookie, that doesn't mean that the entry has not been recorded successfully; the other + bookies that recorded the entry might have failed. +

+ The trick to making everything work is to have a correct idea of a last entry. We do it in roughly three steps: +

+ +
+ Find the entry with the highest last recorded entry, LC; +
+ +
+ +
+ Find the highest consecutively recorded entry, LR; +
+ +
+ +
+ Make sure that all entries between LC and LR are on a quorum of bookies; +
+ +

+ +

+ + + Added: zookeeper/site/trunk/content/doc/r3.4.7/bookkeeperOverview.pdf URL: http://svn.apache.org/viewvc/zookeeper/site/trunk/content/doc/r3.4.7/bookkeeperOverview.pdf?rev=1717709&view=auto ============================================================================== Binary file - no diff available. Propchange: zookeeper/site/trunk/content/doc/r3.4.7/bookkeeperOverview.pdf ------------------------------------------------------------------------------ svn:mime-type = application/pdf Added: zookeeper/site/trunk/content/doc/r3.4.7/bookkeeperProgrammer.html URL: http://svn.apache.org/viewvc/zookeeper/site/trunk/content/doc/r3.4.7/bookkeeperProgrammer.html?rev=1717709&view=auto ============================================================================== --- zookeeper/site/trunk/content/doc/r3.4.7/bookkeeperProgrammer.html (added) +++ zookeeper/site/trunk/content/doc/r3.4.7/bookkeeperProgrammer.html Thu Dec 3 04:29:41 2015 @@ -0,0 +1,1083 @@ + + + + + + + +BookKeeper Getting Started Guide + + + + + + + + + +

+ +

+Apache > ZooKeeper > ZooKeeper +

+ + +

+ +

+ + +

+ +

+ + +

+ + + + + +

+ PDF +

BookKeeper Getting Started Guide

+Programming with BookKeeper +
- + Instantiating BookKeeper. +
- + Creating a ledger. +
- + Adding entries to a ledger. +
- + Closing a ledger. +
- + Opening a ledger. +
- + Reading from ledger +
- + Deleting a ledger +
+

+ + + + + +

Programming with BookKeeper

+ +
+ Instantiating BookKeeper. +
+ +
+ +
+ Creating a ledger. +
+ +
+ +
+ Adding entries to a ledger. +
+ +
+ +
+ Closing a ledger. +
+ +
+ +
+ Opening a ledger. +
+ +
+ +
+ Reading from ledger +
+ +
+ +
+ Deleting a ledger +
+ +

+ +

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: +

+ +
+ +servers is a comma-separated list of ZooKeeper servers. +
+ +

+ + + public BookKeeper(ZooKeeper zk) + throws InterruptedException, KeeperException + + +

+ where: +

+ +
+ +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: +

+ +
+ +zk is a ZooKeeper object. This constructor is useful when + the application also using ZooKeeper and wants to have a single instance of ZooKeeper. +
+ +
+ +
+ +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: +

+ +
+ +ensSize is the number of bookies (ensemble size); +
+ +
+ +
+ +qSize is the write quorum size; +
+ +
+ +
+ +type is the type of digest used with entries: either MAC or CRC32. +
+ +
+ +
+ +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: +

+ +
+ +rc is a return code (please refer to org.apache.bookeeper.client.BKException for a list); +
+ +
+ +
+ +lh is a LedgerHandle object to manipulate a ledger; +
+ +
+ +
+ +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: +

+ +
+ +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: +

+ +
+ +rc is a return code (please refer to org.apache.bookeeper.client.BKDefs for a list); +
+ +
+ +
+ +lh is a LedgerHandle object to manipulate a ledger; +
+ +
+ +
+ +entryId is the identifier of entry associated with this request; +
+ +
+ +
+ +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: +

+ +
+ +rc is a return code (please refer to org.apache.bookeeper.client.BKDefs for a list); +
+ +
+ +
+ +lh is a LedgerHandle object to manipulate a ledger; +
+ +
+ +
+ +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 + + +

+ +
+ +ledgerId is the ledger identifier; +
+ +
+ +
+ +type is the type of digest used with entries: either MAC or CRC32. +
+ +
+ +
+ +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: +

+ +
+ +rc is a return code (please refer to org.apache.bookeeper.client.BKDefs for a list); +
+ +
+ +
+ +lh is a LedgerHandle object to manipulate a ledger; +
+ +
+ +
+ +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 + + +

+ +
+ +firstEntry is the identifier of the first entry in the sequence of entries to read; +
+ +
+ +
+ +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: +

+ +
+ +rc is a return code (please refer to org.apache.bookeeper.client.BKDefs for a list); +
+ +
+ +
+ +lh is a LedgerHandle object to manipulate a ledger; +
+ +
+ +
+ +seq is a Enumeration<LedgerEntry> object to containing the list of entries requested; +
+ +
+ +
+ +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 + + +

+ +
+ +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: +

+ +
+ +rc is a return code (please refer to org.apache.bookeeper.client.BKDefs for a list); +
+ +
+ +
+ +ctx is control object used for accountability purposes. +
+ +

+ +

+ + + Added: zookeeper/site/trunk/content/doc/r3.4.7/bookkeeperProgrammer.pdf URL: http://svn.apache.org/viewvc/zookeeper/site/trunk/content/doc/r3.4.7/bookkeeperProgrammer.pdf?rev=1717709&view=auto ============================================================================== Binary file - no diff available. Propchange: zookeeper/site/trunk/content/doc/r3.4.7/bookkeeperProgrammer.pdf ------------------------------------------------------------------------------ svn:mime-type = application/pdf Added: zookeeper/site/trunk/content/doc/r3.4.7/bookkeeperStarted.html URL: http://svn.apache.org/viewvc/zookeeper/site/trunk/content/doc/r3.4.7/bookkeeperStarted.html?rev=1717709&view=auto ============================================================================== --- zookeeper/site/trunk/content/doc/r3.4.7/bookkeeperStarted.html (added) +++ zookeeper/site/trunk/content/doc/r3.4.7/bookkeeperStarted.html Thu Dec 3 04:29:41 2015 @@ -0,0 +1,448 @@ + + + + + + + +BookKeeper Getting Started Guide + + + + + + + + + +

+ +

+Apache > ZooKeeper > ZooKeeper +

+ + +

+ +

+ + +

+ +

+ + +

+ + + + + +

+ PDF +

BookKeeper Getting Started Guide

+Getting Started: Setting up BookKeeper to write logs. +
- +Pre-requisites +
- +Download +
- +LocalBookKeeper +
- +Setting up bookies +
- +Setting up ZooKeeper +
- +Example +
+

+ + + + + +

Getting Started: Setting up BookKeeper to write logs.

This document contains information to get you started quickly with + BookKeeper. It is aimed primarily at developers willing to try it out, and + contains simple installation instructions for a simple BookKeeper installation + and a simple programming example. For further programming detail, please refer to + BookKeeper Programmer's Guide. +

+ +

Pre-requisites

See + System Requirements in the Admin guide.

+ +

Download

BookKeeper is distributed along with ZooKeeper. To get a ZooKeeper distribution, + download a recent + + stable release from one of the Apache Download + Mirrors.

+ +

LocalBookKeeper

Under org.apache.bookkeeper.util, you'll find a java program + called LocalBookKeeper.java that sets you up to run BookKeeper on a + single machine. This is far from ideal from a performance perspective, + but the program is useful for both test and educational purposes. +

+ +

Setting up bookies

If you're bold and you want more than just running things locally, then + you'll need to run bookies in different servers. You'll need at least three bookies + to start with. +

+ For each bookie, we need to execute a command like the following: +

+ + java -cp .:./zookeeper-<version>-bookkeeper.jar:./zookeeper-<version>.jar\ + :lib/slf4j-api-1.6.1.jar:lib/slf4j-log4j12-1.6.1.jar:lib/log4j-1.2.15.jar -Dlog4j.configuration=log4j.properties\ + org.apache.bookkeeper.proto.BookieServer 3181 127.0.0.1:2181 /path_to_log_device/\ + /path_to_ledger_device/ + +

"/path_to_log_device/" and "/path_to_ledger_device/" are different paths. Also, port 3181 + is the port that a bookie listens on for connection requests from clients. 127.0.0.1:2181 is the hostname:port + for the ZooKeeper server. In this example, the standalone ZooKeeper server is running locally on port 2181. + If we had multiple ZooKeeper servers, this parameter would be a comma separated list of all the hostname:port + values corresponding to them. +

+ +

Setting up ZooKeeper

ZooKeeper stores metadata on behalf of BookKeeper clients and bookies. To get a minimal + ZooKeeper installation to work with BookKeeper, we can set up one server running in + standalone mode. Once we have the server running, we need to create a few znodes: +

+ +
+ + /ledgers + +
+ +
+ +
+ + /ledgers/available + +
+ +
+ +
For each bookie, we add one znode such that the name of the znode is the + concatenation of the machine name and the port number that the bookie is + listening on. For example, if a bookie is running on bookie.foo.com an is listening + on port 3181, we add a znode + /ledgers/available/bookie.foo.com:3181. +
+ +

+ +

Example

+ In the following excerpt of code, we: +

+ +
+ Create a ledger; +
+ +
+ +
+ Write to the ledger; +
+ +
+ +
+ Close the ledger; +
+ +
+ +
+ Open the same ledger for reading; +
+ +
+ +
+ Read from the ledger; +
+ +
+ +
+ Close the ledger again; +
+ +

+LedgerHandle lh = bkc.createLedger(ledgerPassword);
+ledgerId = lh.getId();
+ByteBuffer entry = ByteBuffer.allocate(4);
+
+for(int i = 0; i < 10; i++){
+	entry.putInt(i);
+	entry.position(0);
+	entries.add(entry.array());				
+	lh.addEntry(entry.array());
+}
+lh.close();
+lh = bkc.openLedger(ledgerId, ledgerPassword);		
+			
+Enumeration<LedgerEntry> ls = lh.readEntries(0, 9);
+int i = 0;
+while(ls.hasMoreElements()){
+	ByteBuffer origbb = ByteBuffer.wrap(
+				entries.get(i++));
+	Integer origEntry = origbb.getInt();
+	ByteBuffer result = ByteBuffer.wrap(
+				ls.nextElement().getEntry());
+
+	Integer retrEntry = result.getInt();
+}
+lh.close();
+

+ +

+ + + Added: zookeeper/site/trunk/content/doc/r3.4.7/bookkeeperStarted.pdf URL: http://svn.apache.org/viewvc/zookeeper/site/trunk/content/doc/r3.4.7/bookkeeperStarted.pdf?rev=1717709&view=auto ============================================================================== Binary file - no diff available. Propchange: zookeeper/site/trunk/content/doc/r3.4.7/bookkeeperStarted.pdf ------------------------------------------------------------------------------ svn:mime-type = application/pdf Added: zookeeper/site/trunk/content/doc/r3.4.7/bookkeeperStream.html URL: http://svn.apache.org/viewvc/zookeeper/site/trunk/content/doc/r3.4.7/bookkeeperStream.html?rev=1717709&view=auto ============================================================================== --- zookeeper/site/trunk/content/doc/r3.4.7/bookkeeperStream.html (added) +++ zookeeper/site/trunk/content/doc/r3.4.7/bookkeeperStream.html Thu Dec 3 04:29:41 2015 @@ -0,0 +1,612 @@ + + + + + + + +Streaming with BookKeeper + + + + + + + + + +

+ +

+Apache > ZooKeeper > ZooKeeper +

+ + +

+ +

+ + +

+ +

+ + +

+ + + + + +

+ PDF +

Streaming with BookKeeper

+Summary +
+Writing a stream of bytes +
+Reading a stream of bytes +

+ + + + + +

Summary

+ When using the BookKeeper API, an application has to split the data to write into entries, each + entry being a byte array. This is natural for many applications. For example, when using BookKeeper + for write-ahead logging, an application typically wants to write the modifications corresponding + to a command or a transaction. Some other applications, however, might not have a natural boundary + for entries, and may prefer to write and read streams of bytes. This is exactly the purpose of the + stream API we have implemented on top of BookKeeper. +

+ The stream API is implemented in the package Streaming, and it contains two main classes: LedgerOutputStream and + LedgerInputStream. The class names are indicative of what they do. +

+ + + +

Writing a stream of bytes

+ Class LedgerOutputStream implements two constructors and five public methods: +

+ + + public LedgerOutputStream(LedgerHandle lh) + + +

+ where: +

+ +
+ +lh is a ledger handle for a previously created and open ledger. +
+ +

+ + + public LedgerOutputStream(LedgerHandle lh, int size) + + +

+ where: +

+ +
+ +lh is a ledger handle for a previously created and open ledger. +
+ +
+ +
+ +size is the size of the byte buffer to store written bytes before flushing. +
+ +

+ +Closing a stream. This call closes the stream by flushing the write buffer. +

+ + + public void close() + + +

+ which has no parameters. +

+ +Flushing a stream. This call essentially flushes the write buffer. +

+ + + public synchronized void flush() + + +

+ which has no parameters. +

+ +Writing bytes. There are three calls for writing bytes to a stream. +

+ + + public synchronized void write(byte[] b) + + +

+ where: +

+ +
+ +b is an array of bytes to write. +
+ +

+ + + public synchronized void write(byte[] b, int off, int len) + + +

+ where: +

+ +
+ +b is an array of bytes to write. +
+ +
+ +
+ +off is a buffer offset. +
+ +
+ +
+ +len is the length to write. +
+ +

+ + + public synchronized void write(int b) + + +

+ where: +

+ +
+ +b contains a byte to write. The method writes the least significant byte of the integer four bytes. +
+ +

+ + + +

Reading a stream of bytes

+ Class LedgerOutputStream implements two constructors and four public methods: +

+ + + public LedgerInputStream(LedgerHandle lh) + throws BKException, InterruptedException + + +

+ where: +

+ +
+ +lh is a ledger handle for a previously created and open ledger. +
+ +

+ + + public LedgerInputStream(LedgerHandle lh, int size) + throws BKException, InterruptedException + + +

+ where: +

+ +
+ +lh is a ledger handle for a previously created and open ledger. +
+ +
+ +
+ +size is the size of the byte buffer to store bytes that the application + will eventually read. +
+ +

+ +Closing. There is one call to close an input stream, but the call + is currently empty and the application is responsible for closing the ledger handle. +

+ + + public void close() + + +

+ which has no parameters. +

+ +Reading. There are three calls to read from the stream. +

+ + + public synchronized int read() + throws IOException + + +

+ which has no parameters. +

+ + + public synchronized int read(byte[] b) + throws IOException + + +

+ where: +

+ +
+ +b is a byte array to write to. +
+ +

+ + + public synchronized int read(byte[] b, int off, int len) + throws IOException + + +

+ where: +

+ +
+ +b is a byte array to write to. +
+ +
+ +
+ +off is an offset for byte array b. +
+ +
+ +
+ +len is the length in bytes to write to b. +
+ +

+ +

+ + + Added: zookeeper/site/trunk/content/doc/r3.4.7/bookkeeperStream.pdf URL: http://svn.apache.org/viewvc/zookeeper/site/trunk/content/doc/r3.4.7/bookkeeperStream.pdf?rev=1717709&view=auto ============================================================================== Binary file - no diff available. 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