{"id":676,"date":"2017-11-09T11:48:20","date_gmt":"2017-11-09T19:48:20","guid":{"rendered":"https:\/\/www.kenwalger.com\/blog\/?p=676"},"modified":"2017-11-16T12:43:40","modified_gmt":"2017-11-16T20:43:40","slug":"retryable-writes","status":"publish","type":"post","link":"https:\/\/www.kenwalger.com\/blog\/nosql\/mongodb\/retryable-writes\/","title":{"rendered":"Retryable Writes in MongoDB"},"content":{"rendered":"<p>MongoDB 3.4 offered some <a href=\"https:\/\/www.kenwalger.com\/blog\/nosql\/new-version-new-features\/\">great new features<\/a>.\u00a0MongoDB version 3.6 is quickly approaching a final release date and is introducing many new features too. As I discussed previously, one feature is <a href=\"https:\/\/www.kenwalger.com\/blog\/nosql\/mongodb\/change-streams-coming-soon-mongodb-3-6\/\">change streams<\/a>. Another very exciting and much anticipated new feature is retryable\u00a0writes.<\/p>\n<h3>The Need for Retryable Writes<\/h3>\n<p>In previous versions of <a href=\"https:\/\/www.mongodb.com\">MongoDB<\/a>, it was incumbent upon the developer and the application to handle situations where a write doesn&#8217;t happen. Imagine sending a create or update command to your database and something happens. A network partition occurs,\u00a0a <a href=\"https:\/\/docs.mongodb.com\/manual\/core\/replica-set-elections\/\">primary steps\u00a0down<\/a>, or a <a href=\"https:\/\/www.amazon.com\/gp\/product\/078948983X\/ref=as_li_tl?ie=UTF8&amp;camp=1789&amp;creative=9325&amp;creativeASIN=078948983X&amp;linkCode=as2&amp;tag=kenwalgersite-20&amp;linkId=8afe7c700070a08f2f0053fef2c8416e\" target=\"_blank\" rel=\"noopener\">butterfly<\/a><img loading=\"lazy\" decoding=\"async\" style=\"border: none !important; margin: 0px !important;\" src=\"\/\/ir-na.amazon-adsystem.com\/e\/ir?t=kenwalgersite-20&amp;l=am2&amp;o=1&amp;a=078948983X\" alt=\"\" width=\"1\" height=\"1\" border=\"0\" \/> flaps it&#8217;s wings in <a href=\"https:\/\/www.amazon.com\/gp\/product\/0241245745\/ref=as_li_tl?ie=UTF8&amp;camp=1789&amp;creative=9325&amp;creativeASIN=0241245745&amp;linkCode=as2&amp;tag=kenwalgersite-20&amp;linkId=61f4992dae867976e401b1909bcc3d30\" target=\"_blank\" rel=\"noopener\">Ecuador<\/a><img loading=\"lazy\" decoding=\"async\" style=\"border: none !important; margin: 0px !important;\" src=\"\/\/ir-na.amazon-adsystem.com\/e\/ir?t=kenwalgersite-20&amp;l=am2&amp;o=1&amp;a=0241245745\" alt=\"\" width=\"1\" height=\"1\" border=\"0\" \/> and causes a network malfunction in <a href=\"https:\/\/www.amazon.com\/gp\/product\/B01D6P25O4\/ref=as_li_tl?ie=UTF8&amp;camp=1789&amp;creative=9325&amp;creativeASIN=B01D6P25O4&amp;linkCode=as2&amp;tag=kenwalgersite-20&amp;linkId=4a94952d1dc3aa13dff59353966228ae\" target=\"_blank\" rel=\"noopener\">Chicago<\/a><img loading=\"lazy\" decoding=\"async\" style=\"border: none !important; margin: 0px !important;\" src=\"\/\/ir-na.amazon-adsystem.com\/e\/ir?t=kenwalgersite-20&amp;l=am2&amp;o=1&amp;a=B01D6P25O4\" alt=\"\" width=\"1\" height=\"1\" border=\"0\" \/>. Or any other host of possibilities.<\/p>\n<h3>Driver Handling<\/h3>\n<p>Retryable writes in version 3.6 removes the handling of these system\u00a0failures from the application to the database itself. The MongoDB driver is now capable of automatically retrying many write operations. Meanwhile, the server is in charge of the handling the processing of the write request and the exactly-once concept.<\/p>\n<h6>Supported Retryable Write Operations<\/h6>\n<p>MongoDB 3.6 supports this functionality for single-statement write operations such as:<\/p>\n<ul>\n<li><code>insertOne()<\/code><\/li>\n<li><code>updateOne()<\/code><\/li>\n<li><code>replaceOne()<\/code><\/li>\n<li><code>deleteOne()<\/code><\/li>\n<li><code>findOneAndDelete()<\/code><\/li>\n<li><code>findOneAndReplace()<\/code><\/li>\n<li><code>findOneAndUpdate()<\/code><\/li>\n<\/ul>\n<p>Supported multi-statement operations include <code>insertMany()<\/code> and <code>bulkWrite()<\/code>. Although there are some limitations to using <code>bulkWrite()<\/code> with the new feature.<\/p>\n<h6>Retryable Write Limitations<\/h6>\n<p>In MongoDB 3.6 there are a\u00a0<em>few<\/em> current limitations where retryable\u00a0behavior isn&#8217;t supported. Although these limitations may be removed in the future.<\/p>\n<ol>\n<li>Writes with an unacknowledged write concern, <code>{w: 0}<\/code><\/li>\n<li>Write commands that might affect multiple documents using a single statement<\/li>\n<li>Commands other than insert, delete, update, and findAndModify. For example, aggregation commands using the <code>$out<\/code> operator.<\/li>\n<\/ol>\n<h3>How it Works in a Nutshell<\/h3>\n<p>As I mentioned, retryable\u00a0writes are handled on the server. But it is implemented through the driver through another new feature in MongoDB 3.6, logical sessions. By creating a session with the server, we are now able to establish a unique transaction identifier for each write operation.<\/p>\n<pre>&gt; var session = startSession( { retry_writes : True });\n> session.db.collection.updateOne({'_id': 1}, \n     {'$inc': {'counter': 5}}\n  );\n<\/pre>\n<p>Or in a Python example:<\/p>\n<pre>uri = \"mongodb:\/\/example.com:27017\/?retryWrites=true\"\nclient = MongoClient(uri)\ndatabase = client.database\ncollection = database.collection\n<\/pre>\n<p>This transaction identifier for the session is re-sent to the server, by the driver, to determine the success of a\u00a0<em>previous<\/em> write attempt. This implementation brings with it some big wins.<\/p>\n<ul>\n<li>No extra code is needed for applications, such as save points or retry logic.<\/li>\n<li>Retryable writes aren&#8217;t limited only to idempotent operations.<\/li>\n<li>They are safe for operations that fail acknowledge write success due to timeout exceptions.<\/li>\n<\/ul>\n<h3>Wrap Up<\/h3>\n<p>Retryable writes are yet another great feature brought forth by the team at MongoDB. For applications that simply cannot tolerate\u00a0any loss of write operations,\u00a0retryable writes are a big benefit. One of the many reasons to look at the <a href=\"https:\/\/www.mongodb.com\/download-center\">latest release<\/a> of MongoDB.<\/p>\n<hr \/>\n<p>Follow me on Twitter <a href=\"https:\/\/www.twitter.com\/kenwalger\">@kenwalger<\/a> to get the latest updates on my postings.<\/p>\n<p>There are a few MongoDB specific terms in this post. I created a <a href=\"https:\/\/www.echoskillstore.com\/MongoDB-Dictionary\/45103\">MongoDB Dictionary<\/a> skill for the <a href=\"https:\/\/www.amazon.com\/gp\/product\/B01DFKC2SO\/ref=as_li_tl?ie=UTF8&amp;camp=1789&amp;creative=9325&amp;creativeASIN=B01DFKC2SO&amp;linkCode=as2&amp;tag=kenwalgersite-20&amp;linkId=f9e513223de2525a72b95cf9561db55b\" rel=\"noopener noreferrer\">Amazon Echo<\/a>\u00a0line of products. 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As I discussed previously, one feature is change streams. Another very exciting and much anticipated new feature is retryable\u00a0writes. The Need for Retryable Writes In previous versions of MongoDB, it was incumbent &hellip; <a href=\"https:\/\/www.kenwalger.com\/blog\/nosql\/mongodb\/retryable-writes\/\" class=\"more-link\">Continue reading<span class=\"screen-reader-text\"> &#8220;Retryable Writes in MongoDB&#8221;<\/span><\/a><\/p>\n","protected":false},"author":1,"featured_media":677,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"pmpro_default_level":"","_monsterinsights_skip_tracking":false,"_monsterinsights_sitenote_active":false,"_monsterinsights_sitenote_note":"","_monsterinsights_sitenote_category":0,"jetpack_post_was_ever_published":false,"_jetpack_newsletter_access":"","_jetpack_dont_email_post_to_subs":false,"_jetpack_newsletter_tier_id":0,"_jetpack_memberships_contains_paywalled_content":false,"_jetpack_memberships_contains_paid_content":false,"footnotes":""},"categories":[4],"tags":[1102,1103,1101],"yst_prominent_words":[1056,1091,1061,911,1098,87,1099,1096,336,802,1088,1097,1089,102,1094,1100,1090,803,801,796],"class_list":["post-676","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-mongodb","tag-3-6","tag-new-feature","tag-retryalbe-writes","pmpro-has-access"],"jetpack_featured_media_url":"https:\/\/i0.wp.com\/www.kenwalger.com\/blog\/wp-content\/uploads\/2017\/11\/rw_feature.png?fit=125%2C125&ssl=1","jetpack_sharing_enabled":true,"jetpack_shortlink":"https:\/\/wp.me\/p8lx70-aU","jetpack-related-posts":[],"_links":{"self":[{"href":"https:\/\/www.kenwalger.com\/blog\/wp-json\/wp\/v2\/posts\/676","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/www.kenwalger.com\/blog\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/www.kenwalger.com\/blog\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/www.kenwalger.com\/blog\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/www.kenwalger.com\/blog\/wp-json\/wp\/v2\/comments?post=676"}],"version-history":[{"count":4,"href":"https:\/\/www.kenwalger.com\/blog\/wp-json\/wp\/v2\/posts\/676\/revisions"}],"predecessor-version":[{"id":703,"href":"https:\/\/www.kenwalger.com\/blog\/wp-json\/wp\/v2\/posts\/676\/revisions\/703"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/www.kenwalger.com\/blog\/wp-json\/wp\/v2\/media\/677"}],"wp:attachment":[{"href":"https:\/\/www.kenwalger.com\/blog\/wp-json\/wp\/v2\/media?parent=676"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.kenwalger.com\/blog\/wp-json\/wp\/v2\/categories?post=676"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.kenwalger.com\/blog\/wp-json\/wp\/v2\/tags?post=676"},{"taxonomy":"yst_prominent_words","embeddable":true,"href":"https:\/\/www.kenwalger.com\/blog\/wp-json\/wp\/v2\/yst_prominent_words?post=676"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}