# Twitter News Feed (Timeline) * Home timeline: fan-out write * Search: fan-out read ## Home Timeline ![](https://1250864089-files.gitbook.io/~/files/v0/b/gitbook-legacy-files/o/assets%2F-M4Bkp-b8HYQgJF1rkOc%2F-M5IofXwo0CdSizHPATT%2F-M5Itgz16Q8Qpn7QDnIB%2Fimage.png?alt=media\&token=31a1cbed-b8c4-4358-9ef6-b8b564898ca1) Each write is fanned out 3 times for redundancy purpose. We query the Social Graph Service to fan out the write to all the followers. ![](https://1250864089-files.gitbook.io/~/files/v0/b/gitbook-legacy-files/o/assets%2F-M4Bkp-b8HYQgJF1rkOc%2F-M5IofXwo0CdSizHPATT%2F-M5IuN5gZRA2SrjVVCBu%2Fimage.png?alt=media\&token=07b0720f-ff52-4b8a-908e-876c00ca6045) ![](https://1250864089-files.gitbook.io/~/files/v0/b/gitbook-legacy-files/o/assets%2F-M4Bkp-b8HYQgJF1rkOc%2F-M5IofXwo0CdSizHPATT%2F-M5IsrTwbgcdYxLna13K%2Fimage.png?alt=media\&token=6168c5d8-2213-427b-b416-4d7c3555ae49) Every write is consist of: 1. tweet ID: the sent tweet 2. user ID: the sender's ID 3. bits: miscellaneous product related bits. ![](https://1250864089-files.gitbook.io/~/files/v0/b/gitbook-legacy-files/o/assets%2F-M4Bkp-b8HYQgJF1rkOc%2F-M5IuvvEBb8GAxa4-Btr%2F-M5IvCyqZPzjx_S_ba2P%2Fimage.png?alt=media\&token=d0cb63ed-0591-44f2-ba0c-e6cbcc0e1c25) max limit: 800 tweets in your timeline If you are not a active user (logged in in the last 30 days), we don't fan out write into your timeline. ![](https://1250864089-files.gitbook.io/~/files/v0/b/gitbook-legacy-files/o/assets%2F-M4Bkp-b8HYQgJF1rkOc%2F-M5IviNhowXf-UR6Qf7R%2F-M5IvlAPNeCEjuwOBMzD%2Fimage.png?alt=media\&token=3cf4bc3b-e546-45b4-8598-33d33213f355) If your cache is empty, we will reconstruct your timeline. ## Search ![](https://1250864089-files.gitbook.io/~/files/v0/b/gitbook-legacy-files/o/assets%2F-M4Bkp-b8HYQgJF1rkOc%2F-M5Iw_J_LnpUvKwyZ2Sf%2F-M5IwhvcD8fl-wkXBUQE%2Fimage.png?alt=media\&token=6927f2ef-b6e2-4ddd-a576-bba35c262999) Earlybird is a modified version of Lucene. Twitter mainly rank the contents based on: 1. Re-tweet 2. Like 3. Reply ![](https://1250864089-files.gitbook.io/~/files/v0/b/gitbook-legacy-files/o/assets%2F-M4Bkp-b8HYQgJF1rkOc%2F-M5Iwq_9lj55U7TiAQ8G%2F-M5IxU7m1C5caY-_WpFi%2Fimage.png?alt=media\&token=aabc87e2-bf11-4fe3-afb6-e9e0d2a116fd) The home timeline requires O(n) write and O(1) read The search timeline requires O(1) write and O(n) read ![](https://1250864089-files.gitbook.io/~/files/v0/b/gitbook-legacy-files/o/assets%2F-M4Bkp-b8HYQgJF1rkOc%2F-M5Iwq_9lj55U7TiAQ8G%2F-M5Ixcs3VFE9eDOHP94F%2Fimage.png?alt=media\&token=5b2669ee-71b3-4692-9541-beee97107e6a) ## Improve fanout write Race condition: 1. Lady gaga sends out tweet 2. I retweet or reply 3. My fanout write is done before Lady gaga's is done. 400 million tweets a day, 4600 tweets a second Merge home timeline and search timeline. ![](https://1250864089-files.gitbook.io/~/files/v0/b/gitbook-legacy-files/o/assets%2F-M4Bkp-b8HYQgJF1rkOc%2F-M5IzPSfOETj_cyPHeRR%2F-M5IziVj_zyaRu_jYFUE%2Fimage.png?alt=media\&token=7e8237be-a3ee-4c3c-b9ff-cadef65fce7f) ![](https://1250864089-files.gitbook.io/~/files/v0/b/gitbook-legacy-files/o/assets%2F-M4Bkp-b8HYQgJF1rkOc%2F-M5IzPSfOETj_cyPHeRR%2F-M5J-UQd1ZtSy2yq2JCF%2Fimage.png?alt=media\&token=5b97035a-d60e-4b83-96cf-c7871ec2fbd5) Don't fanout write for users with large number of followers. Only do fan out for users with small number of followers. ![](https://1250864089-files.gitbook.io/~/files/v0/b/gitbook-legacy-files/o/assets%2F-M4Bkp-b8HYQgJF1rkOc%2F-M5IzPSfOETj_cyPHeRR%2F-M5J-eF6943t07Q42Xp7%2Fimage.png?alt=media\&token=6a1eac57-602e-4b5e-96a1-b6b7f75860b8) ![](https://1250864089-files.gitbook.io/~/files/v0/b/gitbook-legacy-files/o/assets%2F-M4Bkp-b8HYQgJF1rkOc%2F-M5IzPSfOETj_cyPHeRR%2F-M5J-y8upoU027LR6jE-%2Fimage.png?alt=media\&token=62b78ae7-54de-40b5-9f5f-86591596079d) ![](https://1250864089-files.gitbook.io/~/files/v0/b/gitbook-legacy-files/o/assets%2F-M4Bkp-b8HYQgJF1rkOc%2F-M5IzPSfOETj_cyPHeRR%2F-M5J-sO53ATe10tSnfP1%2Fimage.png?alt=media\&token=37188704-7e33-4d1f-b4ac-25d2f84e6eb7) ## Stats ![](https://1250864089-files.gitbook.io/~/files/v0/b/gitbook-legacy-files/o/assets%2F-M4Bkp-b8HYQgJF1rkOc%2F-M5IzPSfOETj_cyPHeRR%2F-M5J0QxB5Ko7BcPSyuAn%2Fimage.png?alt=media\&token=6ba6990c-7229-4536-934b-345892dd35a3) ![](https://1250864089-files.gitbook.io/~/files/v0/b/gitbook-legacy-files/o/assets%2F-M4Bkp-b8HYQgJF1rkOc%2F-M5IzPSfOETj_cyPHeRR%2F-M5J0T8jn0AtOJd3d9lj%2Fimage.png?alt=media\&token=9ef82ca9-c8a6-4847-afae-a037ea400fce) ![](https://1250864089-files.gitbook.io/~/files/v0/b/gitbook-legacy-files/o/assets%2F-M4Bkp-b8HYQgJF1rkOc%2F-M5IzPSfOETj_cyPHeRR%2F-M5J0VC0nJmlJmB5JuoB%2Fimage.png?alt=media\&token=e2bd6f33-6bf2-44af-bba5-29203e68609b) ## Reference 1. Timelines at Scale (APR 03, 2013):