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Sometimes I check how many users of mathematica.stackexchange.com there are.
I remember that a few weeks ago there were about 15 thousand and recently I've been surprised seeing that the new users are signed with numbers over 18000.
Let's check this site, the new users therein have numbers slightly over 14000. The registry number of new users included 21 pages with 4 X 9 = 36 new users which is less than 800 << 18000 - 15000.

What is going on?

Let's look at this page, the number of user49115 is 14837 while the next one in the registry is Jazz having the number 15838 i.e 15838 = 14837 + 1001.

I know I can find e.g. how many teachers or students there are, but the number of all users is also interesting.

So what is the reliable number of all users (including unregistered) and of those who are regeistered?

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  • Some of them are bots that get destroyed quickly by spam filters, which might explain the difference.
    – rm -rf Mod
    Jul 17, 2014 at 13:02
  • bots, crocks and frogs Jul 18, 2014 at 15:19
  • @belisarius you mean fraugs
    – Yves Klett
    Jul 20, 2014 at 22:05
  • @rm-rf, it seems there was a different reason. I wonder now if what you are saying is correct, that SE can destroy accounts from bots in the site.
    – carlosayam
    Jul 29, 2014 at 1:46
  • @caya I don't know what exactly SE does behind the scenes, but I certainly can destroy accounts and have done so. That still won't explain a contiguous block of 1000 users missing, so Oded's answer is the only explanation.
    – rm -rf Mod
    Jul 29, 2014 at 2:00

2 Answers 2

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This is due to how our databases are setup and operate.

The Id field (user number) is an auto incrementing field - essentially when a user gets created, it takes the next number (not entirely accurate, there are some wrinkles there, not relevant to this).

We operate with replication - our databases are replicated between data centers to help with backup and for disaster recovery (if a datacenter/database goes down, we have a replica with near to current data).

In our always-on configuration, to avoid too much network chatter between replicas, seeds are pre-allocated in chunks of 1000 (standard behavior for SQL Server 2012 and above, if I understand things correctly).

If there is a replication hiccup, the result is pretty much what you see.

We did upgrade our database servers around the time of this gap - so, it all fits nicely together...

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  • Thanks for explaning the problem. So if I uderstand correctly the registry numbers of new users are not reliable measures of the total number of users?
    – Artes
    Jul 26, 2014 at 23:44
  • @Artes - they never were. The way identity fields work, they will increment also on a failed attempt - so if current max Id is 111, a failed attempt to create a new user will increment the underlying sequence to 112, a successful creation will increment again, to 113, leaving a hole. This is normal for database operations and is one reason to never use these Ids as meaningful.
    – Oded
    Jul 27, 2014 at 9:40
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Now that the technical side of this has been answered I'll attempt to address:

So what is the reliable number of all users (including unregistered) and of those who are registered?

The Stack Exchange User Reputation Leagues page provides some apparently useful data:

Q&A for users of Mathematica (12,957 total users)

It also gives a break-down by reputation which provides a useful way to measure participating members:

Total Reputation
Total Rep*  Users
100,000+    1
50,000+     5
25,000+     17
10,000+     44
5,000+      69
3,000+      95
2,000+      137
1,000+      214
500+        362
200+        728
1+          11,285

Why this page says that we have 1,672 more members than those with 1 reputation point I don't know.

From this data I estimate that we have about one thousand members with a reputation of 100 points, indicating either significant participation or activity on other Stack Exchange sites.

On a personal note I am pleased to see that we have 44 major hitters (10k+) now.

(Update by belisarius follows. User Rep. Leagues as of Feb 10, 2015)

Total Rep*  Users
100,000+    1
50,000+     7
25,000+     20
10,000+     51
5,000+      80
3,000+      116
2,000+      171
1,000+      254
500+        443
200+        898
1+          14,641
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  • Looking at the users tab there are about 5000 users with 100 rep or more (of which about 3300 have 101) Jul 25, 2014 at 21:14
  • The discrepancy might be because unregistered users are not counted in certain places.
    – rm -rf Mod
    Jul 26, 2014 at 0:37
  • Thanks for your answer.
    – Artes
    Jul 27, 2014 at 0:26

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