What posts get deleted, and why?

Question

A fair number of posts get deleted on Server Fault, for a wide variety of reasons and by a diverse set of methods.

Because these posts are, by definition, not visible and not searchable, there tends to be a lot of misinformation about how much gets deleted and who deletes it.

So, for the sake of discussion, let's have some numbers on what has been recently deleted, who deleted it, and why.

_{(I posted these numbers for Stack Overflow a while back, and tend to think it's helped in various discussions there. Hoping they're useful here as well...)}

Answer 1

Here are pie charts for comparison of SF and SO stats (the two sites for which these are available). I made these for SO first, so the categories are in the order of size on SO. The percentages are not exactly the same as in the table, because I omitted some of the obscure reasons for deletion.

Auto N means the script deleting questions after N days.

Moderator deletions and migrations are much more significant on SF. Deletion by 10K users is not very frequent on either site. Among the automatic reasons for deletion, 9-day roomba dominates on SF while 365-day roomba is most prolific on SO.

---

SO authors seemingly love to delete their answers. Maybe because they get downvoted? Again, moderators delete much more on SF (proportionally): directly and indirectly, via deletion of parent question. The yellow Review slice is almost invisible on SF. The cyan slice, answers to migrated questions, is prominent on SF but invisible on SO. A lot of answered questions get migrated away from SF.

Answer 2

27,911 posts were deleted on Server Fault during the past 365 days (query run on Feb. 16th, 2016). That breaks down as follows:

Post Type Deleted by...                                            Posts Deleted % of total 
--------- -------------------------------------------------------- ------------- ---------- 
Question  Auto-deletion: AbandonedClosed                           6105          21.87 %    
Question  Author vote                                              3776          13.53 %    
Answer    Moderator                                                3220          11.54 %    
Question  Auto-deletion: AbandonedQuestions                        2955          10.59 %    
Question  Moderator                                                2035          7.29 %     
Question  Auto-deletion: DeadQuestions                             1777          6.37 %     
Answer    Parent question deleted (Moderator)                      1657          5.94 %     
Question  Auto-deletion: MigrationStubs                            1374          4.92 %     
Answer    Author vote                                              1172          4.20 %     
Answer    Converted to Comment                                     1166          4.18 %     
Answer    Parent question deleted (Auto-deletion: AbandonedClosed) 998           3.58 %     
Answer    Parent question migrated                                 526           1.88 %     
Answer    Spam/Offensive flags                                     239           0.86 %     
Answer    Parent question deleted (Author vote)                    226           0.81 %     
Answer    Parent question deleted (3rd-party vote)                 173           0.62 %     
Question  3rd-party vote                                           116           0.42 %     
Question  Spam/Offensive flags                                     76            0.27 %     
Answer    Parent question migration rejected                       65            0.23 %     
Question  Author was deleted                                       60            0.21 %     
Answer    Author was deleted                                       59            0.21 %     
Answer    Review                                                   48            0.17 %     
Answer    Parent question deleted (Author was deleted)             31            0.11 %     
Answer    Parent question deleted                                  28            0.10 %     
Answer    3rd-party vote                                           16            0.06 %     
Answer    Parent question deleted (via Vote)                       10            0.04 %     
Answer    Parent question deleted (Spam/Offensive flags)           2             0.01 %     
Answer    Parent question deleted (Auto-deletion: MigrationStubs)  1             0.00 %     

Note that during this same time period, 83,140 posts were created.

This looks only at posts that were deleted during this time period and remain deleted. It does not count posts that were deleted and then undeleted, nor does it double-count those that were deleted, undeleted, and then re-deleted. There are arguments to be made for counting all of these things, but they are few in number and mostly just add confusion.

See also: Rules for auto-deletion