# Twitter News Feed (Timeline)
* Home timeline: fan-out write
* Search: fan-out read
## Home Timeline
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.
Every write is consist of:
1. tweet ID: the sent tweet
2. user ID: the sender's ID
3. bits: miscellaneous product related bits.
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.
If your cache is empty, we will reconstruct your timeline.
## Search
Earlybird is a modified version of Lucene.
Twitter mainly rank the contents based on:
1. Re-tweet
2. Like
3. Reply
The home timeline requires O(n) write and O(1) read
The search timeline requires O(1) write and O(n) read
## 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.
Don't fanout write for users with large number of followers. Only do fan out for users with small number of followers.
## Stats
## Reference
1. Timelines at Scale (APR 03, 2013):
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