Category: memcached

Memcached – Useful Resources ”; Previous Next The following resources contain additional information on Memcached. Please use them to get more in-depth knowledge on this topic. Useful Links on Memcached Memcached − Memcached official website. Memcached Downloads − Download latest release of Memcached. Memcached Wiki − A short tutorial on Redis. Useful Books on Memcached To enlist your site on this page, please drop an email to [email protected] Print Page Previous Next Advertisements ”;

Discuss Memcached ”; Previous Next Memcached is an open source, high-performance, distributed memory object caching system. This tutorial provides a basic understanding of all the relevant concepts of Memcached needed to create and deploy a highly scalable and performance-oriented system. Please enable JavaScript to view the comments powered by Disqus. Print Page Previous Next Advertisements ”;

Memcached – Increment Decrement Data ”; Previous Next Memcached incr and decr commands are used to increment or decrement the numeric value of an existing key. If the key is not found, then it returns NOT_FOUND. If the key is not numeric, then it returns CLIENT_ERROR cannot increment or decrement non-numeric value. Otherwise, ERROR is returned. Syntax – incr The basic syntax of Memcached incr command is as shown below − incr key increment_value Example In this example, we use visitors as key and set 10 initially into it, thereafter we increment the visitors by 5. set visitors 0 900 2 10 STORED get visitors VALUE visitors 0 2 10 END incr visitors 5 15 get visitors VALUE visitors 0 2 15 END Syntax – decr The basic syntax of Memcached decr command is as shown below decr key decrement_value Example set visitors 0 900 2 10 STORED get visitors VALUE visitors 0 2 10 END decr visitors 5 5 get visitors VALUE visitors 0 1 5 END Incr/Decr Using Java Application To increment or decrement data in a Memcached server, you need to use Memcached incr or decr methods respectively. Example import net.spy.memcached.MemcachedClient; public class MemcachedJava { public static void main(String[] args) { // Connecting to Memcached server on localhost MemcachedClient mcc = new MemcachedClient(new InetSocketAddress(“127.0.0.1”, 11211)); System.out.println(“Connection to server sucessfully”); System.out.println(“set status:”+mcc.set(“count”, 900, “5”).isDone()); // Get value from cache System.out.println(“Get from Cache:”+mcc.get(“count”)); // now increase the stored value System.out.println(“Increment value:”+mcc.incr(“count”, 2)); // now decrease the stored value System.out.println(“Decrement value:”+mcc.decr(“count”, 1)); // now get the final stored value System.out.println(“Get from Cache:”+mcc.get(“count”)); } } Output On compiling and executing the program, you get to see the following output − Connection to server successfully set status:true Get from Cache:5 Increment value:7 Decrement value:6 Get from Cache:6 Print Page Previous Next Advertisements ”;

Memcached – CAS Command ”; Previous Next CAS stands for Check-And-Set or Compare-And-Swap. Memcached CAS command is used to set the data if it is not updated since last fetch. If the key does not exist in Memcached, then it returns NOT_FOUND. Syntax The basic syntax of Memcached CAS command is as shown below − set key flags exptime bytes unique_cas_key [noreply] value The keywords in the syntax are as described below− key − It is the name of the key by which data is stored and retrieved from Memcached. flags − It is the 32-bit unsigned integer that the server stores with the data provided by the user, and returns along with the data when the item is retrieved. exptime − It is the expiration time in seconds. 0 means no delay. If exptime is more than 30 days, Memcached uses it as a UNIX timestamp for expiration. bytes − It is the number of bytes in the data block that needs to be stored. This is the length of the data that needs to be stored in Memcached. unique_cas_key − It is the unique key get from gets command. noreply (optional) − It is a parameter that informs the server not to send any reply. value − It is the data that needs to be stored. Data needs to be passed on new line after executing the command with the above options. Output The output of the command is as shown below − STORED STORED indicates success. ERROR indicates error while saving data or wrong syntax. EXISTS indicates that someone has modified the CAS data since last fetch. NOT_FOUND indicates that the key does not exist in the Memcached server. Example To execute a CAS command in Memcached, you need to get a CAS token from the Memcached gets command. cas tp 0 900 9 ERROR cas tp 0 900 9 2 memcached set tp 0 900 9 memcached STORED gets tp VALUE tp 0 9 1 memcached END cas tp 0 900 5 2 redis EXISTS cas tp 0 900 5 1 redis STORED get tp VALUE tp 0 5 redis END CAS Using Java Application To get CAS data from a Memcached server, you need to use Memcached gets method. Example import net.spy.memcached.MemcachedClient; public class MemcachedJava { public static void main(String[] args) { // Connecting to Memcached server on localhost MemcachedClient mcc = new MemcachedClient(new InetSocketAddress(“127.0.0.1”, 11211)); System.out.println(“Connection to server successful”); System.out.println(“set status:”+mcc.set(“tutorialspoint”, 900, “memcached”).isDone()); // Get cas token from cache long castToken = mcc.gets(“tutorialspoint”).cas; System.out.println(“Cas token:”+castToken); // now set new data in memcached server System.out.println(“Now set new data:”+mcc.cas(“tutorialspoint”, castToken, 900, “redis”)); System.out.println(“Get from Cache:”+mcc.get(“tutorialspoint”)); } } Output On compiling and executing the program, you get to see the following output − Connection to server successful set status:true Cas token:3 Now set new data:OK Get from Cache:redis Print Page Previous Next Advertisements ”;

Memcached – Stats Items ”; Previous Next Memcached stats items command is used to get items statistics such as count, age, eviction, etc. organized by slabs ID. Syntax The basic syntax of Memcached stats items command is as shown below − stats items Example stats items STAT items:1:number 1 STAT items:1:age 7 STAT items:1:evicted 0 STAT items:1:evicted_nonzero 0 STAT items:1:evicted_time 0 STAT items:1:outofmemory 0 STAT items:1:tailrepairs 0 STAT items:1:reclaimed 0 STAT items:1:expired_unfetched 0 STAT items:1:evicted_unfetched 0 END Print Page Previous Next Advertisements ”;

Memcached – Quick Guide ”; Previous Next Memcached – Overview Memcached is an open source, high-performance, distributed memory caching system intended to speed up dynamic web applications by reducing the database load. It is a key-value dictionary of strings, objects, etc., stored in the memory, resulting from database calls, API calls, or page rendering. Memcached was developed by Brad Fitzpatrick for LiveJournal in 2003. However, it is now being used by Netlog, Facebook, Flickr, Wikipedia, Twitter, and YouTube among others. The key features of Memcached are as follows − It is open source. Memcached server is a big hash table. It significantly reduces the database load It is perfectly efficient for websites with high database load. It is distributed under Berkeley Software Distribution (BSD) license. It is a client-server application over TCP or UDP. Memcached is not − a persistent data store a database application-specific a large object cache fault-tolerant or highly available Memcached – Environment Installing Memcached on Ubuntu To install Memcached on Ubuntu, go to terminal and type the following commands − $sudo apt-get update $sudo apt-get install memcached Confirming Memcached Installation To confirm if Memcached is installed or not, you need to run the command given below. This command shows that Memcached is running on the default port 11211. $ps aux | grep memcached To run Memcached server on a different port, execute the command given below. This command starts the server on the TCP port 11111 and listens on the UDP port 11111 as a daemon process. $memcached -p 11111 -U 11111 -u user -d You can run multiple instances of Memcached server through a single installation. Memcached Java Environment Setup To use Memcached in your Java program, you need to download spymemcached-2.10.3.jar and setup this jar into the classpath. Memcached – Connection To connect to a Memcached server, you need to use the telnet command on HOST and PORT names. Syntax The basic syntax of Memcached telnet command is as shown below − $telnet HOST PORT Here, HOST and PORT are machine IP and port number respectively, on which the Memcached server is executing. Example The following example shows how to connect to a Memcached server and execute a simple set and get command. Assume that the Memcached server is running on host 127.0.0.1 and port 11211. $telnet 127.0.0.1 11211 Trying 127.0.0.1… Connected to 127.0.0.1. Escape character is ”^]”. // now store some data and get it from memcached server set tutorialspoint 0 900 9 memcached STORED get tutorialspoint VALUE tutorialspoint 0 9 memcached END Connection from Java Application To connect the Memcached server from your java program, you need to add the Memcached jar into your classpath as shown in the previous chapter. Assume that the Memcached server is running on host 127.0.0.1 and port 11211. − Example import net.spy.memcached.MemcachedClient; public class MemcachedJava { public static void main(String[] args) { // Connecting to Memcached server on localhost MemcachedClient mcc = new MemcachedClient(new InetSocketAddress(“127.0.0.1”, 11211)); System.out.println(“Connection to server sucessfully”); //not set data into memcached server System.out.println(“set status:”+mcc.set(“tutorialspoint”, 900, “memcached”).done); //Get value from cache System.out.println(“Get from Cache:”+mcc.get(“tutorialspoint”)); } } Output On compiling and executing the program, you get to see the following output − Connection to server successfully set status:true Get from Cache:memcached. The terminal may show few informational messages too, those can be ignored. Memcached – Set Data Memcached set command is used to set a new value to a new or existing key. Syntax The basic syntax of Memcached set command is as shown below − set key flags exptime bytes [noreply] value The keywords in the syntax are as described below − key − It is the name of the key by which data is stored and retrieved from Memcached. flags − It is the 32-bit unsigned integer that the server stores with the data provided by the user, and returns along with the data when the item is retrieved. exptime − It is the expiration time in seconds. 0 means no delay. If exptime is more than 30 days, Memcached uses it as UNIX timestamp for expiration. bytes − It is the number of bytes in the data block that needs to be stored. This is the length of the data that needs to be stored in Memcached. noreply (optional) – It is a parameter that informs the server not to send any reply. value − It is the data that needs to be stored. The data needs to be passed on the new line after executing the command with the above options. Output The output of the command is as shown below − STORED STORED indicates success. ERROR indicates incorrect syntax or error while saving data. Example In the following example, we use tutorialspoint as the key and set value Memcached in it with an expiration time of 900 seconds. set tutorialspoint 0 900 9 memcached STORED get tutorialspoint VALUE tutorialspoint 0 9 Memcached END Set Data Using Java Application To set a key in Memcached server, you need to use Memcached set method. Example import net.spy.memcached.MemcachedClient; public class MemcachedJava { public static void main(String[] args) { // Connecting to Memcached server on localhost MemcachedClient mcc = new MemcachedClient(new InetSocketAddress(“127.0.0.1”, 11211)); System.out.println(“Connection to server sucessfully”); System.out.println(“set status:”+mcc.set(“tutorialspoint”, 900, “memcached”).done); // Get value from cache System.out.println(“Get from Cache:”+mcc.get(“tutorialspoint”)); } } Output On compiling and executing the program, you get to see the following output − Connection to server successfully set status:true Get from Cache:memcached Memcached – Add Data Memcached add command is used to set a value to a new key. If the key already exists, then it gives the output NOT_STORED. Syntax The basic syntax of Memcached add command is as shown below − add key flags exptime bytes [noreply] value The keywords in the syntax are as described below − key − It is the name of the key by which data is stored and retrieved from Memcached. flags − It is the 32-bit unsigned integer that the server stores with the data provided by the

Memcached – Stats Sizes ”; Previous Next Memcached stats sizes command provides information about the sizes and number of items of each size within the cache. The information is returned in two columns. The first column is the size of the item (rounded up to the nearest 32 byte boundary), and the second column is the count of the number of items of that size within the cache. Syntax The basic syntax of Memcached stats sizes command is as shown below − stats sizes Example stats sizes STAT 96 1 END The item size statistics are useful only to determine the sizes of the objects you are storing. Since the actual memory allocation is relevant only in terms of the chunk size and page size, the information is only useful during a careful debugging or diagnostic session. Print Page Previous Next Advertisements ”;

Memcached – Clear Data ”; Previous Next Memcached flush_all command is used to delete all data (key-value pairs) from the Memcached server. It accepts an optional parameter called time that sets a time after which the Memcached data is to be cleared. Syntax The basic syntax of Memcached flush_all command is as shown below − flush_all [time] [noreply] The above command always returns OK. Example In the following example, we store some data into the Memcached server and then clear all the data. set tutorialspoint 0 900 9 memcached STORED get tutorialspoint VALUE tutorialspoint 0 9 memcached END flush_all OK get tutorialspoint END Clear Data Using Java Application To clear data from a Memcached server, you need to use the Memcached flush method. Example import net.spy.memcached.MemcachedClient; public class MemcachedJava { public static void main(String[] args) { // Connecting to Memcached server on localhost MemcachedClient mcc = new MemcachedClient(new InetSocketAddress(“127.0.0.1”, 11211)); System.out.println(“Connection to server sucessfully”); System.out.println(“set status:”+mcc.set(“count”, 900, “5”).isDone()); // Get value from cache System.out.println(“Get from Cache:”+mcc.get(“count”)); // now increase the stored value System.out.println(“Increment value:”+mcc.incr(“count”, 2)); // now decrease the stored value System.out.println(“Decrement value:”+mcc.decr(“count”, 1)); // now get the final stored value System.out.println(“Get from Cache:”+mcc.get(“count”)); // now clear all this data System.out.println(“Clear data:”+mcc.flush().isDone()); } } Output On compiling and executing the program, you get to see the following output − Connection to server successfully set status:true Get from Cache:5 Increment value:7 Decrement value:6 Get from Cache:6 Clear data:true Print Page Previous Next Advertisements ”;

Memcached – Stats ”; Previous Next Memcached stats command is used to return server statistics such as PID, version, connections, etc. Syntax The basic syntax of Memcached stats command is as shown below − stats Example stats STAT pid 1162 STAT uptime 5022 STAT time 1415208270 STAT version 1.4.14 STAT libevent 2.0.19-stable STAT pointer_size 64 STAT rusage_user 0.096006 STAT rusage_system 0.152009 STAT curr_connections 5 STAT total_connections 6 STAT connection_structures 6 STAT reserved_fds 20 STAT cmd_get 6 STAT cmd_set 4 STAT cmd_flush 0 STAT cmd_touch 0 STAT get_hits 4 STAT get_misses 2 STAT delete_misses 1 STAT delete_hits 1 STAT incr_misses 2 STAT incr_hits 1 STAT decr_misses 0 STAT decr_hits 1 STAT cas_misses 0 STAT cas_hits 0 STAT cas_badval 0 STAT touch_hits 0 STAT touch_misses 0 STAT auth_cmds 0 STAT auth_errors 0 STAT bytes_read 262 STAT bytes_written 313 STAT limit_maxbytes 67108864 STAT accepting_conns 1 STAT listen_disabled_num 0 STAT threads 4 STAT conn_yields 0 STAT hash_power_level 16 STAT hash_bytes 524288 STAT hash_is_expanding 0 STAT expired_unfetched 1 STAT evicted_unfetched 0 STAT bytes 142 STAT curr_items 2 STAT total_items 6 STAT evictions 0 STAT reclaimed 1 END Stats Using Java Application To get stats from a Memcached server, you need to use the Memcached stats method. Example import net.spy.memcached.MemcachedClient; public class MemcachedJava { public static void main(String[] args) { // Connecting to Memcached server on localhost MemcachedClient mcc = new MemcachedClient(new InetSocketAddress(“127.0.0.1”, 11211)); System.out.println(“Connection to server successful”); System.out.println(“Stats:”+mcc.stats); } } Output On compiling and executing the program, you get to see the following output − Connection to server successful Stats:[/127.0.0.1:11211:[delete_hits:0, bytes:71, total_items:4, rusage_system:0.220013, touch_misses:0, cmd_touch:0, listen_disabled_num:0, auth_errors:0, evictions:0, version:1.4.14, pointer_size:64, time:1417279366, incr_hits:1, threads:4, expired_unfetched:0, limit_maxbytes:67108864, hash_is_expanding:0, bytes_read:170, curr_connections:8, get_misses:1, reclaimed:0, bytes_written:225, hash_power_level:16, connection_structures:9, cas_hits:0, delete_misses:0, total_connections:11, rusage_user:0.356022, cmd_flush:0, libevent:2.0.19-stable, uptime:12015, reserved_fds:20, touch_hits:0, cas_badval:0, pid:1138, get_hits:2, curr_items:1, cas_misses:0, accepting_conns:1, evicted_unfetched:0, cmd_get:3, cmd_set:2, auth_cmds:0, incr_misses:1, hash_bytes:524288, decr_misses:1, decr_hits:1, conn_yields:0]] Print Page Previous Next Advertisements ”;

Memcached – Stats Slabs ”; Previous Next Memcached stats slabs command displays slabs statistics such as size, memory usage, commands, count etc. organized by slabs ID. Syntax The basic syntax of Memcached stats slabs command is as shown below − stats slabs Example stats slabs STAT 1:chunk_size 96 STAT 1:chunks_per_page 10922 STAT 1:total_pages 1 STAT 1:total_chunks 10922 STAT 1:used_chunks 1 STAT 1:free_chunks 10921 STAT 1:free_chunks_end 0 STAT 1:mem_requested 71 STAT 1:get_hits 0 STAT 1:cmd_set 1 STAT 1:delete_hits 0 STAT 1:incr_hits 0 STAT 1:decr_hits 0 STAT 1:cas_hits 0 STAT 1:cas_badval 0 STAT 1:touch_hits 0 STAT active_slabs 1 STAT total_malloced 1048512 END Print Page Previous Next Advertisements ”;