Quotas

ZooKeeper has both namespace and bytes quotas. You can use the ZooKeeperMain class to setup quotas. + ZooKeeper prints WARN messages if users exceed the quota assigned to them. The messages + are printed in the log of the ZooKeeper. +

+$java -cp zookeeper.jar:src/java/lib/log4j-1.2.15.jar/conf:src/java/lib/jline-0.9.94.jar \ + org.apache.zookeeper.ZooKeeperMain -server host:port +

The above command gives you a command line option of using quotas.

+ +

Setting Quotas

You can use + setquota to set a quota on a ZooKeeper node. It has an option of setting quota with + -n (for namespace) + and -b (for bytes).

The ZooKeeper quota are stored in ZooKeeper itself in /zookeeper/quota. To disable other people from + changing the quota's set the ACL for /zookeeper/quota such that only admins are able to read and write to it. +

+ +

Listing Quotas

You can use + listquota to list a quota on a ZooKeeper node. +

+ +

Deleting Quotas

You can use + delquota to delete quota on a ZooKeeper node. +

+ +

+ + +

+ +

+ + +

+ + + + + +

+ PDF +

ZooKeeper Getting Started Guide

+Getting Started: Coordinating Distributed Applications with + ZooKeeper +
- +Pre-requisites +
- +Download +
- +Standalone Operation +
- +Managing ZooKeeper Storage +
- +Connecting to ZooKeeper +
- +Programming to ZooKeeper +
- +Running Replicated ZooKeeper +
- +Other Optimizations +
+

+ + + + + + +

Getting Started: Coordinating Distributed Applications with + ZooKeeper

This document contains information to get you started quickly with + ZooKeeper. It is aimed primarily at developers hoping to try it out, and + contains simple installation instructions for a single ZooKeeper server, a + few commands to verify that it is running, and a simple programming + example. Finally, as a convenience, there are a few sections regarding + more complicated installations, for example running replicated + deployments, and optimizing the transaction log. However for the complete + instructions for commercial deployments, please refer to the ZooKeeper + Administrator's Guide.

+ +

Pre-requisites

See + System Requirements in the Admin guide.

+ +

Download

To get a ZooKeeper distribution, download a recent + + stable release from one of the Apache Download + Mirrors.

+ +

Standalone Operation

Setting up a ZooKeeper server in standalone mode is + straightforward. The server is contained in a single JAR file, + so installation consists of creating a configuration.

Once you've downloaded a stable ZooKeeper release unpack + it and cd to the root

To start ZooKeeper you need a configuration file. Here is a sample, + create it in conf/zoo.cfg:

+tickTime=2000
+dataDir=/var/zookeeper
+clientPort=2181
+

This file can be called anything, but for the sake of this + discussion call + it conf/zoo.cfg. Change the + value of dataDir to specify an + existing (empty to start with) directory. Here are the meanings + for each of the fields:

+ +tickTime + +: +
the basic time unit in milliseconds used by ZooKeeper. It is + used to do heartbeats and the minimum session timeout will be + twice the tickTime.
+

+ +dataDir + +: +
the location to store the in-memory database snapshots and, + unless specified otherwise, the transaction log of updates to the + database.
+
+ +clientPort + +: +
the port to listen for client connections
+

Now that you created the configuration file, you can start + ZooKeeper:

bin/zkServer.sh start

ZooKeeper logs messages using log4j -- more detail + available in the + Logging + section of the Programmer's Guide. You will see log messages + coming to the console (default) and/or a log file depending on + the log4j configuration.

The steps outlined here run ZooKeeper in standalone mode. There is + no replication, so if ZooKeeper process fails, the service will go down. + This is fine for most development situations, but to run ZooKeeper in + replicated mode, please see Running Replicated + ZooKeeper.

+ +

Managing ZooKeeper Storage

For long running production systems ZooKeeper storage must + be managed externally (dataDir and logs). See the section on + maintenance for + more details.

+ +

Connecting to ZooKeeper

Once ZooKeeper is running, you have several options for connection + to it:

+ +
+Java: Use
+ + +
```
bin/zkCli.sh -server 127.0.0.1:2181
```
+ + +
This lets you perform simple, file-like operations.
+ +
+ +
+C: compile cli_mt + (multi-threaded) or cli_st (single-threaded) by running + make cli_mt or make + cli_st in + the src/c subdirectory in + the ZooKeeper sources. See the README contained within + src/c for full details.
+ + +
You can run the program + from src/c using:
+ + +
```
LD_LIBRARY_PATH=. cli_mt 127.0.0.1:2181
```
+ + +
or
+ + +
```
LD_LIBRARY_PATH=. cli_st 127.0.0.1:2181
```
+ +
This will give you a simple shell to execute file + system like operations on ZooKeeper.
+ +

Once you have connected, you should see something like: +

+
+Connecting to localhost:2181
+log4j:WARN No appenders could be found for logger (org.apache.zookeeper.ZooKeeper).
+log4j:WARN Please initialize the log4j system properly.
+Welcome to ZooKeeper!
+JLine support is enabled
+[zkshell: 0]
+

+ From the shell, type help to get a listing of commands that can be executed from the client, as in: +

+
+[zkshell: 0] help
+ZooKeeper host:port cmd args
+        get path [watch]
+        ls path [watch]
+        set path data [version]
+        delquota [-n|-b] path
+        quit
+        printwatches on|off
+        createpath data acl
+        stat path [watch]
+        listquota path
+        history
+        setAcl path acl
+        getAcl path
+        sync path
+        redo cmdno
+        addauth scheme auth
+        delete path [version]
+        setquota -n|-b val path
+
+

From here, you can try a few simple commands to get a feel for this simple command line interface. First, start by issuing the list command, as + in ls, yielding: +

+
+[zkshell: 8] ls /
+[zookeeper]
+

Next, create a new znode by running create /zk_test my_data. This creates a new znode and associates the string "my_data" with the node. + You should see:

+
+[zkshell: 9] create /zk_test my_data
+Created /zk_test
+

Issue another ls / command to see what the directory looks like: +

+
+[zkshell: 11] ls /
+[zookeeper, zk_test]
+
+

+ Notice that the zk_test directory has now been created. +

Next, verify that the data was associated with the znode by running the get command, as in: +

+
+[zkshell: 12] get /zk_test
+my_data
+cZxid = 5
+ctime = Fri Jun 05 13:57:06 PDT 2009
+mZxid = 5
+mtime = Fri Jun 05 13:57:06 PDT 2009
+pZxid = 5
+cversion = 0
+dataVersion = 0
+aclVersion = 0
+ephemeralOwner = 0
+dataLength = 7
+numChildren = 0
+

We can change the data associated with zk_test by issuing the set command, as in: +

+
+[zkshell: 14] set /zk_test junk
+cZxid = 5
+ctime = Fri Jun 05 13:57:06 PDT 2009
+mZxid = 6
+mtime = Fri Jun 05 14:01:52 PDT 2009
+pZxid = 5
+cversion = 0
+dataVersion = 1
+aclVersion = 0
+ephemeralOwner = 0
+dataLength = 4
+numChildren = 0
+[zkshell: 15] get /zk_test
+junk
+cZxid = 5
+ctime = Fri Jun 05 13:57:06 PDT 2009
+mZxid = 6
+mtime = Fri Jun 05 14:01:52 PDT 2009
+pZxid = 5
+cversion = 0
+dataVersion = 1
+aclVersion = 0
+ephemeralOwner = 0
+dataLength = 4
+numChildren = 0
+

+ (Notice we did a get after setting the data and it did, indeed, change.

Finally, let's delete the node by issuing: +

+
+[zkshell: 16] delete /zk_test
+[zkshell: 17] ls /
+[zookeeper]
+[zkshell: 18]
+

That's it for now. To explore more, continue with the rest of this document and see the Programmer's Guide.

+ +

Programming to ZooKeeper

ZooKeeper has a Java bindings and C bindings. They are + functionally equivalent. The C bindings exist in two variants: single + threaded and multi-threaded. These differ only in how the messaging loop + is done. For more information, see the Programming + Examples in the ZooKeeper Programmer's Guide for + sample code using of the different APIs.

+ +

Running Replicated ZooKeeper

Running ZooKeeper in standalone mode is convenient for evaluation, + some development, and testing. But in production, you should run + ZooKeeper in replicated mode. A replicated group of servers in the same + application is called a quorum, and in replicated + mode, all servers in the quorum have copies of the same configuration + file. The file is similar to the one used in standalone mode, but with a + few differences. Here is an example:

+tickTime=2000
+dataDir=/var/zookeeper
+clientPort=2181
+initLimit=5
+syncLimit=2
+server.1=zoo1:2888:3888
+server.2=zoo2:2888:3888
+server.3=zoo3:2888:3888
+

The new entry, initLimit is + timeouts ZooKeeper uses to limit the length of time the ZooKeeper + servers in quorum have to connect to a leader. The entry syncLimit limits how far out of date a server can + be from a leader.

With both of these timeouts, you specify the unit of time using + tickTime. In this example, the timeout + for initLimit is 5 ticks at 2000 milleseconds a tick, or 10 + seconds.

The entries of the form server.X list the + servers that make up the ZooKeeper service. When the server starts up, + it knows which server it is by looking for the file + myid in the data directory. That file has the + contains the server number, in ASCII.

Finally, note the two port numbers after each server + name: " 2888" and "3888". Peers use the former port to connect + to other peers. Such a connection is necessary so that peers + can communicate, for example, to agree upon the order of + updates. More specifically, a ZooKeeper server uses this port + to connect followers to the leader. When a new leader arises, a + follower opens a TCP connection to the leader using this + port. Because the default leader election also uses TCP, we + currently require another port for leader election. This is the + second port in the server entry. +

Note

+ +

If you want to test multiple servers on a single + machine, specify the servername + as localhost with unique quorum & + leader election ports (i.e. 2888:3888, 2889:3889, 2890:3890 in + the example above) for each server.X in that server's config + file. Of course separate dataDirs and + distinct clientPorts are also necessary + (in the above replicated example, running on a + single localhost, you would still have + three config files).

+ +

Other Optimizations

There are a couple of other configuration parameters that can + greatly increase performance:

+ +
To get low latencies on updates it is important to + have a dedicated transaction log directory. By default + transaction logs are put in the same directory as the data + snapshots and myid file. The dataLogDir + parameters indicates a different directory to use for the + transaction logs.
+ +
+ +
+[tbd: what is the other config param?] +
+ +

+ +

ZooKeeper Quota's Guide

A Guide to Deployment and Administration