{"id":835,"date":"2023-02-13T16:07:26","date_gmt":"2023-02-13T16:07:26","guid":{"rendered":"https:\/\/www.allendowney.com\/blog\/?p=835"},"modified":"2023-02-13T16:07:26","modified_gmt":"2023-02-13T16:07:26","slug":"one-queue-or-two","status":"publish","type":"post","link":"https:\/\/www.allendowney.com\/blog\/2023\/02\/13\/one-queue-or-two\/","title":{"rendered":"One Queue or Two"},"content":{"rendered":"\n<p>I&#8217;m happy to report that copyediting of <em>Modeling and Simulation in Python<\/em> is done, and the book is off to the printer! Electronic versions are available now from <a href=\"https:\/\/nostarch.com\/modeling-and-simulation-python\">No Starch Press<\/a>; print copies will be available in May, but you can pre-order now from <a href=\"https:\/\/nostarch.com\/modeling-and-simulation-python\">No Starch Press<\/a>, <a href=\"https:\/\/amzn.to\/3ltkXH4\">Amazon<\/a>, and <a href=\"https:\/\/www.barnesandnoble.com\/w\/modeling-and-simulation-in-python-allen-b-downey\/1143009378?ean=9781718502161\">Barnes and Noble<\/a>.<\/p>\n\n\n\n<p>To celebrate, I just published one of the case studies from the end of Part I, which is about simulating discrete systems. The case study explores a classic question from queueing theory:<\/p>\n\n\n\n<blockquote class=\"wp-block-quote is-layout-flow wp-block-quote-is-layout-flow\">\n<p>Suppose you are designing the checkout area for a new store. There is room for two checkout counters and a waiting area for customers. You can make two lines, one for each counter, or one line that serves both counters.<\/p>\n\n\n\n<p>In theory, you might expect a single line to be better, but it has some practical drawbacks: in order to maintain a single line, you would have to install rope barriers, and customers might be put off by what seems to be a longer line, even if it moves faster.<\/p>\n\n\n\n<p>So you\u2019d like to check whether the single line is really better and by how much. <\/p>\n\n\n\n<p><\/p>\n<\/blockquote>\n\n\n\n<p>Simulation can help answer this question. The following figure shows the three scenarios I simulated:<\/p>\n\n\n\n<figure class=\"wp-block-image size-large is-resized\"><img loading=\"lazy\" decoding=\"async\" src=\"https:\/\/github.com\/AllenDowney\/ModSim\/raw\/main\/figs\/queue.png\" alt=\"\" width=\"634\" height=\"152\"\/><\/figure>\n\n\n\n<p>The leftmost diagram shows a single queue (with customers arriving at rate \ud835\udf06) and a single server (with customers completing service at rate \ud835\udf07).<\/p>\n\n\n\n<p>The center diagram shows a single queue with two servers, and the rightmost diagram shows two queue with two servers.<\/p>\n\n\n\n<p>So, which is the best, and by how much? You can <a href=\"https:\/\/allendowney.github.io\/ModSimPy\/queue.html\">read my answer in the online version of the book<\/a>. Or you can <a href=\"https:\/\/colab.research.google.com\/github\/AllenDowney\/ModSimPy\/blob\/master\/examples\/queue.ipynb\">run the Jupyter notebook on Colab<\/a>.<\/p>\n\n\n\n<p>Here&#8217;s what some of the results look like:<\/p>\n\n\n\n<figure class=\"wp-block-image size-full\"><img loading=\"lazy\" decoding=\"async\" width=\"629\" height=\"470\" src=\"https:\/\/www.allendowney.com\/blog\/wp-content\/uploads\/2023\/01\/image.png\" alt=\"\" class=\"wp-image-837\" srcset=\"https:\/\/www.allendowney.com\/blog\/wp-content\/uploads\/2023\/01\/image.png 629w, https:\/\/www.allendowney.com\/blog\/wp-content\/uploads\/2023\/01\/image-300x224.png 300w, https:\/\/www.allendowney.com\/blog\/wp-content\/uploads\/2023\/01\/image-361x270.png 361w\" sizes=\"auto, (max-width: 629px) 100vw, 629px\" \/><\/figure>\n\n\n\n<p>This figure shows the time customers are in the system, including wait time and service time, as a function of the arrival rate. The orange line shows the average we expect based on analysis; the blue dots show the result of simulations.<\/p>\n\n\n\n<p>This comparison shows that the simulation and analysis are consistent. It also demonstrates one of the features of simulation: it is easy to quantify not just the average we expect but also the variation around the average.<\/p>\n\n\n\n<p>That capability turns out to be useful for this problem because, as it turns out, the difference between the one-queue and two-queue scenarios is small compared to the variation, which suggests the advantage would be unnoticed in practice.<\/p>\n\n\n\n<p>I conclude:<\/p>\n\n\n\n<blockquote class=\"wp-block-quote is-layout-flow wp-block-quote-is-layout-flow\">\n<p>The two configurations are equally good as long as both servers are busy; the only time two lines is worse is if one queue is empty and the other contains more than one customer. In real life, if we allow customers to change lanes, that disadvantage can be eliminated.<\/p>\n\n\n\n<p>From a theoretical point of view, one line is better. From a practical point of view, the difference is small and can be mitigated. So the best choice depends on practical considerations.<\/p>\n\n\n\n<p>On the other hand, you can do substantially better with an express line for customers with short service times. But that&#8217;s a topic for another case study.<\/p>\n<\/blockquote>\n","protected":false},"excerpt":{"rendered":"<p>I&#8217;m happy to report that copyediting of Modeling and Simulation in Python is done, and the book is off to the printer! Electronic versions are available now from No Starch Press; print copies will be available in May, but you can pre-order now from No Starch Press, Amazon, and Barnes and Noble. To celebrate, I just published one of the case studies from the end of Part I, which is about simulating discrete systems. The case study explores a classic&#8230;<\/p>\n<p class=\"read-more\"><a class=\"btn btn-default\" href=\"https:\/\/www.allendowney.com\/blog\/2023\/02\/13\/one-queue-or-two\/\"> Read More<span class=\"screen-reader-text\">  Read More<\/span><\/a><\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"closed","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"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":"","jetpack_publicize_message":"","jetpack_publicize_feature_enabled":true,"jetpack_social_post_already_shared":true,"jetpack_social_options":{"image_generator_settings":{"template":"highway","default_image_id":0,"font":"","enabled":false},"version":2}},"categories":[1],"tags":[],"class_list":["post-835","post","type-post","status-publish","format-standard","hentry","category-uncategorized"],"yoast_head":"<!-- This site is optimized with the Yoast SEO plugin v26.5 - https:\/\/yoast.com\/wordpress\/plugins\/seo\/ -->\n<title>One Queue or Two - Probably Overthinking It<\/title>\n<meta name=\"robots\" content=\"index, follow, max-snippet:-1, max-image-preview:large, max-video-preview:-1\" \/>\n<link rel=\"canonical\" href=\"https:\/\/www.allendowney.com\/blog\/2023\/02\/13\/one-queue-or-two\/\" \/>\n<meta property=\"og:locale\" content=\"en_US\" \/>\n<meta property=\"og:type\" content=\"article\" \/>\n<meta property=\"og:title\" content=\"One Queue or Two - Probably Overthinking It\" \/>\n<meta property=\"og:description\" content=\"I&#8217;m happy to report that copyediting of Modeling and Simulation in Python is done, and the book is off to the printer! 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I know this because it's the topic of\u2026","rel":"","context":"Similar post","block_context":{"text":"Similar post","link":""},"img":{"alt_text":"","src":"https:\/\/i0.wp.com\/www.allendowney.com\/blog\/wp-content\/uploads\/2023\/10\/Screenshot-at-2023-10-06-18-00-06.png?resize=350%2C200&ssl=1","width":350,"height":200,"srcset":"https:\/\/i0.wp.com\/www.allendowney.com\/blog\/wp-content\/uploads\/2023\/10\/Screenshot-at-2023-10-06-18-00-06.png?resize=350%2C200&ssl=1 1x, https:\/\/i0.wp.com\/www.allendowney.com\/blog\/wp-content\/uploads\/2023\/10\/Screenshot-at-2023-10-06-18-00-06.png?resize=525%2C300&ssl=1 1.5x, https:\/\/i0.wp.com\/www.allendowney.com\/blog\/wp-content\/uploads\/2023\/10\/Screenshot-at-2023-10-06-18-00-06.png?resize=700%2C400&ssl=1 2x"},"classes":[]},{"id":1071,"url":"https:\/\/www.allendowney.com\/blog\/2023\/10\/22\/the-world-population-singularity\/","url_meta":{"origin":835,"position":1},"title":"The World Population Singularity","author":"AllenDowney","date":"October 22, 2023","format":false,"excerpt":"One of the exercises in Modeling and Simulation in Python invites readers to download estimates of world population from 10,000 BCE to the present, and to see if they are well modeled by any simple mathematical function. Here's what the estimates look like (aggregated on Wikipedia from several researchers and\u2026","rel":"","context":"Similar post","block_context":{"text":"Similar post","link":""},"img":{"alt_text":"","src":"https:\/\/i0.wp.com\/www.allendowney.com\/blog\/wp-content\/uploads\/2023\/10\/image-14.png?resize=350%2C200&ssl=1","width":350,"height":200},"classes":[]},{"id":1034,"url":"https:\/\/www.allendowney.com\/blog\/2023\/10\/02\/what-size-is-that-correlation\/","url_meta":{"origin":835,"position":2},"title":"What size is that correlation?","author":"AllenDowney","date":"October 2, 2023","format":false,"excerpt":"This article is related to Chapter 6 of Probably Overthinking It, which is available for preorder now. It is also related to a new course at Brilliant.org, Explaining Variation. Suppose you find a correlation of 0.36. How would you characterize it? I posed this question to the stalwart few still\u2026","rel":"","context":"Similar post","block_context":{"text":"Similar post","link":""},"img":{"alt_text":"","src":"https:\/\/i0.wp.com\/www.allendowney.com\/blog\/wp-content\/uploads\/2023\/10\/Screenshot-at-2023-10-01-13-51-49.png?resize=350%2C200&ssl=1","width":350,"height":200,"srcset":"https:\/\/i0.wp.com\/www.allendowney.com\/blog\/wp-content\/uploads\/2023\/10\/Screenshot-at-2023-10-01-13-51-49.png?resize=350%2C200&ssl=1 1x, https:\/\/i0.wp.com\/www.allendowney.com\/blog\/wp-content\/uploads\/2023\/10\/Screenshot-at-2023-10-01-13-51-49.png?resize=525%2C300&ssl=1 1.5x, https:\/\/i0.wp.com\/www.allendowney.com\/blog\/wp-content\/uploads\/2023\/10\/Screenshot-at-2023-10-01-13-51-49.png?resize=700%2C400&ssl=1 2x"},"classes":[]},{"id":1477,"url":"https:\/\/www.allendowney.com\/blog\/2025\/01\/04\/confidence-in-the-press\/","url_meta":{"origin":835,"position":3},"title":"Confidence In the Press","author":"AllenDowney","date":"January 4, 2025","format":false,"excerpt":"This is the fifth in a series of excerpts from Elements of Data Science, now available from Lulu.com and online booksellers. It\u2019s based on Chapter 16, which is part of the political alignment case study. You can read the complete example here, or run the Jupyter notebook on Colab. Because\u2026","rel":"","context":"Similar post","block_context":{"text":"Similar post","link":""},"img":{"alt_text":"","src":"https:\/\/i0.wp.com\/www.allendowney.com\/blog\/wp-content\/uploads\/2025\/01\/f652e115b3186a827e67d0882df2218fecf3f5466985f3da007a09e983e93aa6.png?resize=350%2C200&ssl=1","width":350,"height":200},"classes":[]},{"id":1334,"url":"https:\/\/www.allendowney.com\/blog\/2024\/07\/17\/elements-of-data-science\/","url_meta":{"origin":835,"position":4},"title":"Elements of Data Science","author":"AllenDowney","date":"July 17, 2024","format":false,"excerpt":"I'm excited to announce the launch of my newest book, Elements of Data Science. As the subtitle suggests, it is about \"Getting started with Data Science and Python\". Order now from Lulu.com and get 20% off! I am publishing this book myself, which has one big advantage: I can print\u2026","rel":"","context":"Similar post","block_context":{"text":"Similar post","link":""},"img":{"alt_text":"","src":"https:\/\/i0.wp.com\/www.allendowney.com\/blog\/wp-content\/uploads\/2024\/07\/image.png?resize=350%2C200&ssl=1","width":350,"height":200,"srcset":"https:\/\/i0.wp.com\/www.allendowney.com\/blog\/wp-content\/uploads\/2024\/07\/image.png?resize=350%2C200&ssl=1 1x, https:\/\/i0.wp.com\/www.allendowney.com\/blog\/wp-content\/uploads\/2024\/07\/image.png?resize=525%2C300&ssl=1 1.5x"},"classes":[]},{"id":451,"url":"https:\/\/www.allendowney.com\/blog\/2020\/06\/03\/think-dsp-v1-1\/","url_meta":{"origin":835,"position":5},"title":"Think DSP v1.1","author":"AllenDowney","date":"June 3, 2020","format":false,"excerpt":"For the last week or so I have been working on an update to Think DSP. The latest version is available now from Green Tea Press. Here are some of the changes I made: Running on Colab All notebooks now run on Colab. Judging by my inbox, many readers find\u2026","rel":"","context":"In \"digital signal processing\"","block_context":{"text":"digital signal processing","link":"https:\/\/www.allendowney.com\/blog\/tag\/digital-signal-processing\/"},"img":{"alt_text":"","src":"","width":0,"height":0},"classes":[]}],"_links":{"self":[{"href":"https:\/\/www.allendowney.com\/blog\/wp-json\/wp\/v2\/posts\/835","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/www.allendowney.com\/blog\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/www.allendowney.com\/blog\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/www.allendowney.com\/blog\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/www.allendowney.com\/blog\/wp-json\/wp\/v2\/comments?post=835"}],"version-history":[{"count":3,"href":"https:\/\/www.allendowney.com\/blog\/wp-json\/wp\/v2\/posts\/835\/revisions"}],"predecessor-version":[{"id":857,"href":"https:\/\/www.allendowney.com\/blog\/wp-json\/wp\/v2\/posts\/835\/revisions\/857"}],"wp:attachment":[{"href":"https:\/\/www.allendowney.com\/blog\/wp-json\/wp\/v2\/media?parent=835"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.allendowney.com\/blog\/wp-json\/wp\/v2\/categories?post=835"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.allendowney.com\/blog\/wp-json\/wp\/v2\/tags?post=835"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}