Redis Best Practices

Redis-BestPractices-General.md

Some of the Redis best practices content has moved

This content from this markdown file has moved a new, happier home where it can serve more people. Please check it out : https://docs.microsoft.com/azure/azure-cache-for-redis/cache-best-practices.

NOTE: Client specific guidance listed below is still valid and should still be considered. I will update this document once all content has been moved.

Redis-BestPractices-Java-Jedis.md

Jedis Java Client

Jedis instances are single threaded

• Don't use the same Jedis connection instance from multiple threads at the same time.
• Using the same Jedis instance from multiple threads at the same time will result in socket connection errors/resets or strange error messages like "expected '$' but got ' '".

Use JedisPool

• This allows you to talk to redis from multiple threads while still getting the benefits of reused connections.
• The JedisPool object is thread-safe and can be used from multiple threads at the same time.
• This pool should be configured once and reused.
• Make sure to return the Jedis instance back to the pool when done, otherwise you will leak the connection.
• We have seen a few cases where connections in the pool get into a bad state. As a failsafe, you may want to re-create the JedisPool if you see connection errors that continue for longer than 30 seconds.

Some important settings to consider:

Setting	Description
connectTimeout	How long to allow for new connections to be established (in milliseconds). In general, this should be at least 5000ms. If your client application tends to have high spikes CPU usage, setting this to 15000ms or 20000ms would be a good idea.
soTimeout	This configures the socket timeout (in milliseconds) for the underlying connection. You can basically think of this as the operation timeout (how long you are willing to wait for a response from Redis). Think about this one in terms of worst case, not best case. Setting this too low can cause you to get timeout errors due to unexpected bursts in load. I typically recommend 1000ms as a good value for most customers.
port	In Azure, 6379 is non-ssl and 6380 is SSL/TLS. Important Note: 6379 is disabled by default - you have to explicitly enable this insecure port if you wish to use it.

Choose JedisPoolConfig settings with care

Setting	Description
maxTotal	This setting controls the max number of connections that can be created at a given time. Given that Jedis connections cannot be shared across threads, this setting affects the amount of concurrency your application can have when talking to Redis. Note that each connection does have some memory and CPU overhead, so setting this to a very high value may have negative side effects. If not set, the default value is 8, which is probably too low for most applications. When chosing a value, consider how many concurrent calls into Redis you think you will have under load.
maxIdle	This is the max number of connections that can be idle in the pool without being immediately evicted (closed). If not set, the default value is 8. I would recommend that this setting be configured the same as maxTotal to help avoid connection ramp-up costs when your application has many bursts of load in a short period of time. If a connection is idle for a long time, it will still be evicted until the idle connection count hits minIdle (described below).
minIdle	This is the number of "warm" connections (e.g. ready for immediate use) that remain in the pool even when load has reduced. If not set, the default is 0. When choosing a value, consider your steady-state concurrent requests to Redis. For instance, if your application is calling into Redis from 10 threads simultaneously, then you should set this to at least 10 (probably a bit higher to give you some room.
blockWhenExhausted	This controls behavior when a thread asks for a connection, but there aren't any that are free and the pool can't create more (due to maxTotal). If set to true, the calling thread will block for maxWaitMillis before throwing an exception. The default is true and I recommend true for production environments. You could set it to false in testing environments to help you more easily discover what value to use for maxTotal.
maxWaitMillis	How long to wait in milliseconds if calling JedisPool.getResource() will block. The default is -1, which means block indefinitely. I would set this to the same as the socketTimeout configured. Related to blockWhenExhausted.
TestOnBorrow	Controls whether or not the connection is tested before it is returned from the pool. The default is false. Setting to true may increase resilience to connection blips but may also have a performance cost when taking connections from the pool. In my quick testing, I saw a noticable increase in the 50th percentile latencies, but no significant increase in 98th percentile latencies.
minEvictableIdleTimeMillis	This specifies the minimum amount of time an connection may sit idle in the pool before it is eligible for eviction due to idle time. The default value is 60 seconds for JedisPoolConfig, and 30 minutes if you construct a configuration with GenericObjectPoolConfig. Azure Redis currently has 10 minute idle timeout for connections, so this should be set to less than 10 minutes

Use Pipelining

• This will improve the throughput of the application. Read more about redis pipelining here https://redis.io/topics/pipelining.
• Jedis does not do pipelining automatically for you. You have to call diffeent APIs in order to get the significant performance benefits that can come from using pipelining.
• Examples can be found here

Log Pool Usage Periodically

• Debugging performance problems due to JedisPool contention issues will be easier if you log the pool usage regularly.
• If you ever get an error when trying to get a connection from the pool, you should definitely log usage stats. There is sample code here that shows which values to log...

Sample Code

• Here are some links to some sample code demonstrating these best practices
  • https://gist.github.com/JonCole/925630df72be1351b21440625ff2671f#file-redis-samplecode-java-jedispool-java
  • https://gist.github.com/deepakverma/9aa4dc04ded700603a8ef24eececf5d3

Redis-BestPractices-Node-js.md

Node.js

Avoid Idle Connections

Azure Redis currently has 10 minute idle timeout for connections, which will cause short network blips if your connection has long periods of inactivity. The most common Node.js libraries should automatically reconnect.

However, you can avoid this brief connectivity loss if your application sends a PING command on connections to prevent them from being idle. Some client libraries send this ping automatically.

At the time of this writing, the node.js redis client library I tested (node_redis) did NOT do this automatically. You can do this yourself by adding a timer that sends PING command every minute or two. Below is an example of how to do this.

    setInterval(function(){
    	console.log('redisClient => Sending Ping...');
    	redisClient.ping();
    }, 60000); // 60 seconds

Recreate the Connection

We have seen a few cases where a node_redis connection gets into a bad state and can no longer successfully send commands to Redis even though other clients are actively able to interact with Redis. If you see connection issues that last longer than some threshold (say 30 seconds), then you may want to add logic to your app that forcefully recreates the connection instead of waiting for node_redis to reconnect.

Redis-BestPractices-PHP.md

PHP

Reuse Connections

The most common problem we have seen with PHP clients is that they either don't support persistent connections or the ability to reuse connections is disabled by default. When you don't reuse connections, it means that you have to pay the cost of establishing a new connection, including the SSL/TLS handshake, each time you want to send a request. This can add a lot of latency to your request time and will manifest itself as a performance problem in your application. Additionally, if you have a high request rate, this can cause significant CPU churn on both the Redis client-side and server-side, which can result in other issues.

As an example, the Predis Redis client has a "persistent" connection property that is false by default. Setting the "persistent" property to true will should improve behavior drastically.

Redis-BestPractices-Session-State-Provider.md

ASP.Net Session State Provider

Session State Best Practices

1. Enable session state only on required pages - This will avoid known session state provider performance problems.
   • You can disable session state by setting the web.config enableSessionState option to false.

     <system.web>
       <pages enableSessionState=false>
     

   • You can enable it on specific pages by setting the page directive's EnableSessionState option to true

     <%@ Page EnableSessionState=true %>
     

   • Mark pages using Session State as ReadOnly whenever possible - this helps avoid locking contention.

     <%@ Page EnableSessionState=ReadOnly %>
     

2. Avoid Session State (or at least use ReadOnly) on pages that have long load times - When a page with write-access to the session state takes a long time to load, it will hold the lock for that session until the load completes. This can prevent other requests for other pages for the same session from loading. Also, the session state module in ASP.NET will, in the background, continue to ask for the session lock for any additional requests for that same session until the lock is available or until the executionTime is exceeded for the lock. This can generate additional load on your session state store.
3. Make sure you understand the impact of session state locks. Read this article for an example of why this is important.
4. Select your httpRuntime/executionTime carefully - The executionTime you select is the duration that the session lock is held should the app crash without releasing the lock. Select a value that is as low as possible while still meeting your application's specific requirements.

Note: None of these recommendations are specific to Redis - they are good recommendations regardless of which SessionStateProvider you use. Also, some of these recommendations are based on this article, which has additional recommendations beyond those specifically called out here.

Redis-BestPractices-StackExchange-Redis.md

StackExchange.Redis

General Guidance

1. Set AbortConnect to false, then let the ConnectionMultiplexer reconnect automatically. See here for details

2. Reuse the ConnectionMultiplexer - do not create a new one for each request. The Lazy<ConnectionMultiplexer> pattern shown here is strongly recommended.

3. Configure your ThreadPool settings to avoid timeouts.

4. Be aware of the performance costs associated with different operations you are running. For instance, the "KEYS" command is an O(n) operation and should be avoided. The redis.io site has details around the time complexity for each operation that it supports.

5. Consider turning on "Server GC". "Workstation GC" is the default and can impact the latencies when garbage collection is in happening.

6. Most customers find that a single ConnectionMultiplexer is sufficient for their needs. However, if you have high throughput requirements, you may consider slowly increasing the number of connections to see if you get an improvement in throughput. Avoid setting it to an arbitrarily large number of connections as it may not give the desired benefit.

7. Configure supported TLS settings. If you are targeting .NET 4.7 or later, you should not have to do anything because StackExchange.Redis will automatically use the OS level settings when deciding which TLS versions to support (which is a good thing in most cases). If you are targeting an older version of .NET, then you should configure the client to use the highest TLS version that your client system supports (typically TLS 1.2). Once you move to a newer version of the .NET framework, then you should probably remove this configuration and let the OS settings take precedence. This can configured through the sslProtocols connection string entry (requires NuGet package version 1.2.3 or later), or through the ConfigurationOptions class as show here:

   var options = ConfigurationOptions.Parse(connectionString);

   options.SslProtocols = System.Security.Authentication.SslProtocols.Tls12;

   ConnectionMultiplexer.Connect(options);

Reconnecting with Lazy<T> pattern

We have seen a few rare cases where StackExchange.Redis fails to reconnect after a connection blip (for example, due to patching). Restarting the client or creating a new ConnectionMultiplexer will fix the issue. Here is some sample code that still uses the recommended Lazy<ConnectionMultiplexer>pattern while allowing apps to force a reconnection periodically. Make sure to update code calling into the ConnectionMultiplexer so that they handle any ObjectDisposedException errors that occur as a result of disposing the old one.

Redis-LazyReconnect.cs

using System;
using System.Threading;
using StackExchange.Redis;

static class Redis
{
    static long lastReconnectTicks = DateTimeOffset.MinValue.UtcTicks;
    static DateTimeOffset firstError = DateTimeOffset.MinValue;
    static DateTimeOffset previousError = DateTimeOffset.MinValue;

    static object reconnectLock = new object();

    // In general, let StackExchange.Redis handle most reconnects, 
    // so limit the frequency of how often this will actually reconnect.
    public static TimeSpan ReconnectMinFrequency = TimeSpan.FromSeconds(60);

    // if errors continue for longer than the below threshold, then the 
    // multiplexer seems to not be reconnecting, so re-create the multiplexer
    public static TimeSpan ReconnectErrorThreshold = TimeSpan.FromSeconds(30);

    static string connectionString = "TODO: CALL InitializeConnectionString() method with connection string";
    static Lazy<ConnectionMultiplexer> multiplexer = CreateMultiplexer();

    public static ConnectionMultiplexer Connection { get { return multiplexer.Value; } }

    public static void InitializeConnectionString(string cnxString)
    {
        if (string.IsNullOrWhiteSpace(cnxString))
            throw new ArgumentNullException(nameof(cnxString));

        connectionString = cnxString;
    }

    /// <summary>
    /// Force a new ConnectionMultiplexer to be created.  
    /// NOTES: 
    ///     1. Users of the ConnectionMultiplexer MUST handle ObjectDisposedExceptions, which can now happen as a result of calling ForceReconnect()
    ///     2. Don't call ForceReconnect for Timeouts, just for RedisConnectionExceptions or SocketExceptions
    ///     3. Call this method every time you see a connection exception, the code will wait to reconnect:
    ///         a. for at least the "ReconnectErrorThreshold" time of repeated errors before actually reconnecting
    ///         b. not reconnect more frequently than configured in "ReconnectMinFrequency"

    /// </summary>    
    public static void ForceReconnect()
    {
        var utcNow = DateTimeOffset.UtcNow;
        var previousTicks = Interlocked.Read(ref lastReconnectTicks);
        var previousReconnect = new DateTimeOffset(previousTicks, TimeSpan.Zero);
        var elapsedSinceLastReconnect = utcNow - previousReconnect;

        // If mulitple threads call ForceReconnect at the same time, we only want to honor one of them.
        if (elapsedSinceLastReconnect > ReconnectMinFrequency)
        {
            lock (reconnectLock)
            {
                utcNow = DateTimeOffset.UtcNow;
                elapsedSinceLastReconnect = utcNow - previousReconnect;

                if (firstError == DateTimeOffset.MinValue)
                {
                    // We haven't seen an error since last reconnect, so set initial values.
                    firstError = utcNow;
                    previousError = utcNow;
                    return;
                }

                if (elapsedSinceLastReconnect < ReconnectMinFrequency)
                    return; // Some other thread made it through the check and the lock, so nothing to do.

                var elapsedSinceFirstError = utcNow - firstError;
                var elapsedSinceMostRecentError = utcNow - previousError;

                var shouldReconnect =
                    elapsedSinceFirstError >= ReconnectErrorThreshold   // make sure we gave the multiplexer enough time to reconnect on its own if it can
                    && elapsedSinceMostRecentError <= ReconnectErrorThreshold; //make sure we aren't working on stale data (e.g. if there was a gap in errors, don't reconnect yet).

                // Update the previousError timestamp to be now (e.g. this reconnect request)
                previousError = utcNow;

                if (shouldReconnect)
                {
                    firstError = DateTimeOffset.MinValue;
                    previousError = DateTimeOffset.MinValue;

                    var oldMultiplexer = multiplexer;
                    CloseMultiplexer(oldMultiplexer);
                    multiplexer = CreateMultiplexer();
                    Interlocked.Exchange(ref lastReconnectTicks, utcNow.UtcTicks);
                }
            }
        }
    }

    private static Lazy<ConnectionMultiplexer> CreateMultiplexer()
    {
        return new Lazy<ConnectionMultiplexer>(() => ConnectionMultiplexer.Connect(connectionString));
    }

    private static void CloseMultiplexer(Lazy<ConnectionMultiplexer> oldMultiplexer)
    {
        if (oldMultiplexer != null)
        {
            try
            {
                oldMultiplexer.Value.Close();
            }
            catch (Exception)
            {
                // Example error condition: if accessing old.Value causes a connection attempt and that fails.
            }
        }
    }
}

Redis-SampleCode-Java-JedisPool.java

import javax.net.ssl.HostnameVerifier;
import javax.net.ssl.SSLPeerUnverifiedException;
import javax.net.ssl.SSLSession;
import redis.clients.jedis.*;
import javax.net.ssl.*;

public class Redis {
    private static Object staticLock = new Object();
    private static JedisPool pool;
    private static String host;
    private static int port; // 6379 for NonSSL, 6380 for SSL
    private static int connectTimeout; //milliseconds
    private static int operationTimeout; //milliseconds
    private static String password;
    private static JedisPoolConfig config;

    // Should be called exactly once during App Startup logic.
    public static void initializeSettings(String host, int port, String password, int connectTimeout, int operationTimeout) {
        Redis.host = host;
        Redis.port = port;
        Redis.password = password;
        Redis.connectTimeout = connectTimeout;
        Redis.operationTimeout = operationTimeout;
    }

    // MAKE SURE to call the initializeSettings method first
    public static JedisPool getPoolInstance() {
        if (pool == null) { // avoid synchronization lock if initialization has already happened
            synchronized(staticLock) {
                if (pool == null) { // don't re-initialize if another thread beat us to it.
                    JedisPoolConfig poolConfig = getPoolConfig();
                    boolean useSsl = port == 6380 ? true : false;
                    int db = 0;
                    String clientName = "MyClientName"; // null means use default
                    SSLSocketFactory sslSocketFactory = null; // null means use default
                    SSLParameters sslParameters = null; // null means use default
                    HostnameVerifier hostnameVerifier = new SimpleHostNameVerifier(host);
                    pool = new JedisPool(poolConfig, host, port, connectTimeout,operationTimeout,password, db,
                            clientName, useSsl, sslSocketFactory, sslParameters, hostnameVerifier);
                }
            }
        }
        return pool;
    }

    public static JedisPoolConfig getPoolConfig() {
        if (config == null) {
            JedisPoolConfig poolConfig = new JedisPoolConfig();

            // Each thread trying to access Redis needs its own Jedis instance from the pool.
            // Using too small a value here can lead to performance problems, too big and you have wasted resources.
            int maxConnections = 200;
            poolConfig.setMaxTotal(maxConnections);
            poolConfig.setMaxIdle(maxConnections);

            // Using "false" here will make it easier to debug when your maxTotal/minIdle/etc settings need adjusting.
            // Setting it to "true" will result better behavior when unexpected load hits in production
            poolConfig.setBlockWhenExhausted(true);

            // How long to wait before throwing when pool is exhausted
            poolConfig.setMaxWaitMillis(operationTimeout);

            // This controls the number of connections that should be maintained for bursts of load.
            // Increase this value when you see pool.getResource() taking a long time to complete under burst scenarios
            poolConfig.setMinIdle(50);

            Redis.config = poolConfig;
        }

        return config;
    }

    public static String getPoolCurrentUsage()
    {
        JedisPool jedisPool = getPoolInstance();
        JedisPoolConfig poolConfig = getPoolConfig();

        int active = jedisPool.getNumActive();
        int idle = jedisPool.getNumIdle();
        int total = active + idle;
        String log = String.format(
                "JedisPool: Active=%d, Idle=%d, Waiters=%d, total=%d, maxTotal=%d, minIdle=%d, maxIdle=%d",
                active,
                idle,
                jedisPool.getNumWaiters(),
                total,
                poolConfig.getMaxTotal(),
                poolConfig.getMinIdle(),
                poolConfig.getMaxIdle()
        );

        return log;
    }

    private static class SimpleHostNameVerifier implements HostnameVerifier {

        private String exactCN;
        private String wildCardCN;
        public SimpleHostNameVerifier(String cacheHostname)
        {
            exactCN = "CN=" + cacheHostname;
            wildCardCN = "CN=*" + cacheHostname.substring(cacheHostname.indexOf('.'));
        }

        public boolean verify(String s, SSLSession sslSession) {
            try {
                String cn = sslSession.getPeerPrincipal().getName();
                return cn.equalsIgnoreCase(wildCardCN) || cn.equalsIgnoreCase(exactCN);
            } catch (SSLPeerUnverifiedException ex) {
                return false;
            }
        }
    }
}