{"id":12280,"date":"2023-11-11T07:35:13","date_gmt":"2023-11-11T14:35:13","guid":{"rendered":"https:\/\/www.mysqltutorial.org\/?page_id=12280"},"modified":"2023-11-12T22:16:56","modified_gmt":"2023-11-13T05:16:56","slug":"mysql-memory-storage-engine","status":"publish","type":"page","link":"https:\/\/www.mysqltutorial.org\/mysql-administration\/mysql-memory-storage-engine\/","title":{"rendered":"MySQL MEMORY Storage Engine"},"content":{"rendered":"\n<p><strong>Summary<\/strong>: In this tutorial, you will learn about the MySQL <code>MEMORY<\/code> storage engine and how to use it to improve the speed of temporary data retrieval.<\/p>\n\n\n\n<h2 class=\"wp-block-heading\">Introduction to MySQL MEMORY storage engine<\/h2>\n\n\n\n<p>The <code>MEMORY<\/code> storage engine allows you to create a table whose data is stored entirely in the memory of the server.<\/p>\n\n\n\n<p>The <code>MEMORY<\/code> storage engine is useful when you want to store data in the memory for fast access. For example:<\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li><strong>Caching<\/strong>: You can use <code>MEMORY<\/code> tables to cache frequently accessed data that rarely change. It can significantly improve the performance of read-heavy applications by serving data directly from memory.<\/li>\n\n\n\n<li><strong>Session Data<\/strong>: Storing session data of web applications in <code>MEMORY<\/code> tables can improve the response time because it is faster to read and write data from memory.<\/li>\n\n\n\n<li><strong>Temporary tables<\/strong>: You can also use the <code>MEMORY<\/code> tables for temporary storage such as intermediate results of complex queries. They&#8217;re often faster than disk-based storage engines.<\/li>\n<\/ul>\n\n\n\n<p class=\"note\">Note that the <code>MEMORY<\/code> storage engine was previously called <code>HEAP<\/code>.<\/p>\n\n\n\n<p>To create a <code>MEMORY<\/code> table, you use the <a href=\"https:\/\/www.mysqltutorial.org\/mysql-basics\/mysql-create-table\/\">CREATE TABLE<\/a> statement and set the <code>ENGINE<\/code> clause to <code>MEMORY<\/code>:<\/p>\n\n\n<pre class=\"wp-block-code\"><span><code class=\"hljs\">CREATE TABLE table_name(\n   ... \n) ENGINE = MEMORY;<\/code><\/span><\/pre>\n\n\n<p>When you create a <code>MEMORY<\/code> table, the storage engine saves the table definition in the MySQL database dictionary.<\/p>\n\n\n\n<p>If the MySQL database server restarts, the data in the memory table will be swapped out, while the table definition remains intact.<\/p>\n\n\n\n<h2 class=\"wp-block-heading\">MySQL MEMORY storage engine example<\/h2>\n\n\n\n<p>Let&#8217;s take an example of using MySQL <code>MEMORY<\/code> storage engine.<\/p>\n\n\n\n<h3 class=\"wp-block-heading\">1) Creating a MEMORY table<\/h3>\n\n\n\n<p>The following <code><a href=\"https:\/\/www.mysqltutorial.org\/mysql-basics\/mysql-create-table\/\">CREATE TABLE<\/a><\/code> statement creates a table called <code>caches<\/code> with the <code>MEMORY<\/code> storage engine:<\/p>\n\n\n<pre class=\"wp-block-code\" aria-describedby=\"shcb-language-1\" data-shcb-language-name=\"SQL (Structured Query Language)\" data-shcb-language-slug=\"sql\"><span><code class=\"hljs language-sql\"><span class=\"hljs-keyword\">CREATE<\/span> <span class=\"hljs-keyword\">TABLE<\/span> caches (\n   <span class=\"hljs-keyword\">id<\/span> <span class=\"hljs-built_in\">INT<\/span>\n) <span class=\"hljs-keyword\">ENGINE<\/span> = <span class=\"hljs-keyword\">MEMORY<\/span>;<\/code><\/span><small class=\"shcb-language\" id=\"shcb-language-1\"><span class=\"shcb-language__label\">Code language:<\/span> <span class=\"shcb-language__name\">SQL (Structured Query Language)<\/span> <span class=\"shcb-language__paren\">(<\/span><span class=\"shcb-language__slug\">sql<\/span><span class=\"shcb-language__paren\">)<\/span><\/small><\/pre>\n\n\n<p>The <code>caches<\/code> table has one column with the data type <code>INT<\/code>.<\/p>\n\n\n\n<h3 class=\"wp-block-heading\">2) Insert data into a MEMORY table<\/h3>\n\n\n\n<p>The following statement <a href=\"https:\/\/www.mysqltutorial.org\/mysql-basics\/mysql-insert-multiple-rows\/\">inserts three rows<\/a> into the <code>caches<\/code> table:<\/p>\n\n\n<pre class=\"wp-block-code\" aria-describedby=\"shcb-language-2\" data-shcb-language-name=\"SQL (Structured Query Language)\" data-shcb-language-slug=\"sql\"><span><code class=\"hljs language-sql\"><span class=\"hljs-keyword\">INSERT<\/span> <span class=\"hljs-keyword\">INTO<\/span> caches(<span class=\"hljs-keyword\">id<\/span>) \n<span class=\"hljs-keyword\">VALUES<\/span> \n  (<span class=\"hljs-number\">1<\/span>), \n  (<span class=\"hljs-number\">2<\/span>), \n  (<span class=\"hljs-number\">3<\/span>);<\/code><\/span><small class=\"shcb-language\" id=\"shcb-language-2\"><span class=\"shcb-language__label\">Code language:<\/span> <span class=\"shcb-language__name\">SQL (Structured Query Language)<\/span> <span class=\"shcb-language__paren\">(<\/span><span class=\"shcb-language__slug\">sql<\/span><span class=\"shcb-language__paren\">)<\/span><\/small><\/pre>\n\n\n<h3 class=\"wp-block-heading\">3) Query data from the MEMORY table<\/h3>\n\n\n\n<p>The following statement retrieves data from the <code>caches<\/code> table:<\/p>\n\n\n<pre class=\"wp-block-code\" aria-describedby=\"shcb-language-3\" data-shcb-language-name=\"SQL (Structured Query Language)\" data-shcb-language-slug=\"sql\"><span><code class=\"hljs language-sql\"><span class=\"hljs-keyword\">SELECT<\/span> <span class=\"hljs-keyword\">id<\/span> <span class=\"hljs-keyword\">FROM<\/span> caches;<\/code><\/span><small class=\"shcb-language\" id=\"shcb-language-3\"><span class=\"shcb-language__label\">Code language:<\/span> <span class=\"shcb-language__name\">SQL (Structured Query Language)<\/span> <span class=\"shcb-language__paren\">(<\/span><span class=\"shcb-language__slug\">sql<\/span><span class=\"shcb-language__paren\">)<\/span><\/small><\/pre>\n\n\n<p>Output:<\/p>\n\n\n<pre class=\"wp-block-code\" aria-describedby=\"shcb-language-4\" data-shcb-language-name=\"JavaScript\" data-shcb-language-slug=\"javascript\"><span><code class=\"hljs language-javascript\">+------+\n| id   |\n+------+\n|    <span class=\"hljs-number\">1<\/span> |\n|    <span class=\"hljs-number\">2<\/span> |\n|    <span class=\"hljs-number\">3<\/span> |\n+------+\n<span class=\"hljs-number\">3<\/span> rows <span class=\"hljs-keyword\">in<\/span> <span class=\"hljs-keyword\">set<\/span> (0.00 sec)<\/code><\/span><small class=\"shcb-language\" id=\"shcb-language-4\"><span class=\"shcb-language__label\">Code language:<\/span> <span class=\"shcb-language__name\">JavaScript<\/span> <span class=\"shcb-language__paren\">(<\/span><span class=\"shcb-language__slug\">javascript<\/span><span class=\"shcb-language__paren\">)<\/span><\/small><\/pre>\n\n\n<p>If you <a href=\"https:\/\/www.mysqltutorial.org\/mysql-adminsitration\/restart-mysql\/\">restart the MySQL server<\/a>, the data in the <code>caches<\/code> table will be lost, and the above query will return no rows.<\/p>\n\n\n\n<h2 class=\"wp-block-heading\">Summary<\/h2>\n\n\n\n<ul class=\"wp-block-list\">\n<li>The <code>MEMORY<\/code> storage engine stores table data entirely in the memory.<\/li>\n\n\n\n<li>The data in a <code>MEMORY<\/code> table will be lost if the MySQL Server restarts, while the table definitions persist in the MySQL dictionary.<\/li>\n<\/ul>\n<div class=\"helpful-block-content\" data-title=\"\">\n\t<header>\n\t\t<div class=\"wth-question\">Was this tutorial helpful? <\/div>\n\t\t<div 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