# The \_id information in a collection entry is really unique?

**URL:** <https://discourse.getcockpit.com/t/the-id-information-in-a-collection-entry-is-really-unique/2045>\
**Category:** Support\
**Created:** [August 19, 2021, 8:39am UTC](https://discourse.getcockpit.com/t/the-id-information-in-a-collection-entry-is-really-unique/2045 "2021-08-19T08:39:42Z")\
**Posts on this page:** 5\
**Page:** 1

<div class="post-metadata">

**Author:** ![MarcTabaries](https://yyz2.discourse-cdn.com/flex030/user_avatar/discourse.getcockpit.com/marctabaries/32/867_2.png) [@MarcTabaries](https://discourse.getcockpit.com/u/MarcTabaries)\
**Post date:** [August 19, 2021, 8:39am UTC](https://discourse.getcockpit.com/t/the-id-information-in-a-collection-entry-is-really-unique/2045/1 "2021-08-19T08:39:42Z")

</div>

Hello,

I need to know if the \_id of the entries in a collection are really unique and if there is a risk that the same \_id is present in different, or a same, collections.

I plan to use this \_id for an e-commerce site project, but I need to be sure that the generated \_id is really unique.

I can’t find this information in the documentation.

Thanks in advance.

---

<div class="post-metadata">

**Author:** ![abernh](https://yyz2.discourse-cdn.com/flex030/user_avatar/discourse.getcockpit.com/abernh/32/859_2.png) [@abernh](https://discourse.getcockpit.com/u/abernh)\
**Post date:** [August 19, 2021, 8:54pm UTC](https://discourse.getcockpit.com/t/the-id-information-in-a-collection-entry-is-really-unique/2045/2 "2021-08-19T20:54:07Z")

</div>

This is the function generating your collection documents `_id`s

> <https://github.com/agentejo/cockpit/blob/8856aa2cd2ccf1c92bef6374ba238aa02ca080d3/lib/MongoLite/Database.php#L527>

It uses if available either

```auto
  $objId = new \MongoDB\BSON\ObjectId();

```

(which is what MongoDB normally uses for their `_id`s [https://docs.mongodb.com/manual/core/index-unique/;](https://docs.mongodb.com/manual/core/index-unique/;) see also [Generating Globally Unique Identifiers for Use with MongoDB | MongoDB Blog](https://www.mongodb.com/blog/post/generating-globally-unique-identifiers-for-use-with-mongodb) )

or a “mongo db like id”, based on

- the timestamp in ms
- a “random” 5 char integer
- a “random” 2-3 char integer

binaried, hashed and hexed.

Both seem to be setup to create a very unique ID in forever UNLESS you generate

- MongoDB: \> 16million items within 1 second ( [https://betterprogramming.pub/is-the-id-property-in-mongodb-100-unique-f1eaa19522ba#dd87](https://betterprogramming.pub/is-the-id-property-in-mongodb-100-unique-f1eaa19522ba#dd87) )
- MongoLike: \> 88million items at the same microsecond (?\*)

\*) 89000 \* 990 ~ 88mill

---

<div class="post-metadata">

**Author:** ![MarcTabaries](https://yyz2.discourse-cdn.com/flex030/user_avatar/discourse.getcockpit.com/marctabaries/32/867_2.png) [@MarcTabaries](https://discourse.getcockpit.com/u/MarcTabaries)\
**Post date:** [August 23, 2021, 9:17am UTC](https://discourse.getcockpit.com/t/the-id-information-in-a-collection-entry-is-really-unique/2045/3 "2021-08-23T09:17:47Z")

</div>

Ok, thanks for this reply !

---

<div class="post-metadata">

**Author:** ![abernh](https://yyz2.discourse-cdn.com/flex030/user_avatar/discourse.getcockpit.com/abernh/32/859_2.png) [@abernh](https://discourse.getcockpit.com/u/abernh)\
**Post date:** [August 27, 2021, 12:48pm UTC](https://discourse.getcockpit.com/t/the-id-information-in-a-collection-entry-is-really-unique/2045/4 "2021-08-27T12:48:30Z")

</div>

There is currently a bug, causing a relative high chance of duplicate IDs for MongoLite on fast import processes.

> <https://github.com/agentejo/cockpit/issues/1002>
>
> We have integrated Cockpit to our own system. The system creates collection entr…ies based on what we have in our own database. When starting with an empty Cockpit CMS, the initial import creates thousands of collections entries using the API as fast as possible.
> 
> This results in duplicate \_id values for some (but not all) of the entries that were created at the same second (same timestamp in \_created field). 
> 
> \`\`\`
> SELECT json\_extract(Games5c3340b034ba2.document,'$.\_id') as id, count(\*) as count
> FROM Games5c3340b034ba2
> GROUP BY json\_extract(Games5c3340b034ba2.document,'$.\_id') 
> HAVING count \> 1;
> 
> 5c40b42966623700110001b8|2
> 5c40b4296662370011000389|2
> 5c40b42966623700120003b1|2
> 5c40b42a666237001100011c|2
> 5c40b42c666237001200012f|2
> 5c40b42c66623700150000fc|2
> 5c40b42d666237001400009d|2
> 5c40b42d66623700140001a5|2
> 5c40b42d6662370016000245|2
> 5c40b42e6662370014000237|2
> 5c40b42e666237001500009f|2
> 5c40b431666237001300005d|2
> 5c40b438666237001300028b|2
> 5c40b438666237001500031d|2
> 5c40b43966623700120001f2|2
> 5c40b439666237001300001a|2
> 5c40b439666237001300024e|2
> 5c40b43c666237001600039a|2
> 5c40b44066623700140001c7|2
> 5c40b4446662370011000377|2
> 5c40b444666237001200030d|2
> \`\`\`
> 
> I checked that these duplicate \_id values are found only for entries that have the same creation/modify timestamp. Here's one example (timestamp: 1547744300) where you can see that a couple of entries have the same \_id:
> 
> \`\`\`
> sqlite\> SELECT json\_extract(Games5c3340b034ba2.document,'$.\_id') as id, json\_extract(Games5c3340b034ba2.document,'$.gameID') 
> ...\> FROM Games5c3340b034ba2
> ...\> WHERE json\_extract(Games5c3340b034ba2.document,'$.\_created') = 1547744300
> ...\> order by json\_extract(Games5c3340b034ba2.document,'$.\_id');
> 5c40b42c6662370012000019|434
> 5c40b42c666237001200001e|7710
> 5c40b42c666237001200005e|763
> 5c40b42c666237001200007a|607
> 5c40b42c666237001200007f|1373
> 5c40b42c66623700120000ab|193
> 5c40b42c66623700120000bc|787
> 5c40b42c66623700120000df|1326
> 5c40b42c666237001200012f|2209
> 5c40b42c666237001200012f|4028
> 5c40b42c6662370012000144|1220
> 5c40b42c666237001200014c|274
> 5c40b42c666237001200015b|837
> 5c40b42c666237001200015e|7699
> 5c40b42c666237001200017c|462
> 5c40b42c66623700120001a3|4055
> 5c40b42c66623700120001d9|302
> 5c40b42c6662370012000220|1490
> 5c40b42c6662370012000257|131
> 5c40b42c666237001200027a|6354
> 5c40b42c666237001200027d|715
> 5c40b42c666237001200029d|886
> 5c40b42c66623700120002aa|523
> 5c40b42c6662370012000309|748
> 5c40b42c6662370012000321|1111
> 5c40b42c6662370012000345|1078
> 5c40b42c666237001200035e|7709
> 5c40b42c66623700120003a2|2609
> 5c40b42c66623700120003b9|681
> 5c40b42c66623700120003d0|2699
> 5c40b42c6662370013000017|6049
> 5c40b42c6662370013000043|1492
> 5c40b42c666237001300004e|2719
> 5c40b42c6662370013000059|2737
> 5c40b42c666237001300007f|1231
> 5c40b42c66623700130000a1|881
> 5c40b42c6662370013000120|397
> 5c40b42c6662370013000143|6176
> 5c40b42c6662370013000157|411
> 5c40b42c666237001300015f|801
> 5c40b42c6662370013000185|2542
> 5c40b42c666237001300019e|6732
> 5c40b42c66623700130001a4|2600
> 5c40b42c66623700130001ae|330
> 5c40b42c66623700130001c2|1292
> 5c40b42c66623700130001d3|7071
> 5c40b42c66623700130001e8|959
> 5c40b42c6662370013000216|2046
> 5c40b42c6662370013000235|6266
> 5c40b42c6662370013000286|259
> 5c40b42c66623700130002b6|1338
> 5c40b42c66623700130002e9|1165
> 5c40b42c66623700130002f7|662
> 5c40b42c6662370013000304|6472
> 5c40b42c666237001300034e|2030
> 5c40b42c6662370013000380|1427
> 5c40b42c6662370013000392|659
> 5c40b42c6662370013000393|358
> 5c40b42c6662370013000397|7700
> 5c40b42c666237001300039b|6831
> 5c40b42c6662370015000019|366
> 5c40b42c6662370015000059|2626
> 5c40b42c6662370015000062|6555
> 5c40b42c6662370015000080|2717
> 5c40b42c6662370015000086|1351
> 5c40b42c66623700150000bb|2604
> 5c40b42c66623700150000f4|871
> 5c40b42c66623700150000fc|1155
> 5c40b42c66623700150000fc|2504
> 5c40b42c6662370015000104|1235
> 5c40b42c6662370015000139|1260
> 5c40b42c6662370015000197|1191
> 5c40b42c66623700150001fe|937
> 5c40b42c6662370015000204|694
> 5c40b42c6662370015000215|6024
> 5c40b42c666237001500021e|2565
> 5c40b42c666237001500023c|657
> 5c40b42c666237001500023d|2650
> 5c40b42c6662370015000272|910
> 5c40b42c666237001500028c|872
> 5c40b42c66623700150002bd|1463
> 5c40b42c6662370015000320|1508
> 5c40b42c6662370015000323|420
> 5c40b42c666237001500032c|7639
> 5c40b42c666237001500033e|2557
> 5c40b42c666237001500035a|6063
> 5c40b42c666237001500038e|196
> 5c40b42c66623700150003d5|892
> 5c40b42c66623700150003d8|2017
> \`\`\`
> 
> We are using the latest Docker image.

A PR with a fix was pushed ( [fix (Bug 1002:createMongoDbLikeId): microsecond float to big integer … by abernh · Pull Request #1465 · agente](https://github.com/agentejo/cockpit/pull/1465) ) and should be available soon.

---

<div class="post-metadata">

**Author:** ![abernh](https://yyz2.discourse-cdn.com/flex030/user_avatar/discourse.getcockpit.com/abernh/32/859_2.png) [@abernh](https://discourse.getcockpit.com/u/abernh)\
**Post date:** [September 28, 2021, 8:21am UTC](https://discourse.getcockpit.com/t/the-id-information-in-a-collection-entry-is-really-unique/2045/5 "2021-09-28T08:21:02Z")

</div>

> There is currently a bug, causing a relative high chance of duplicate IDs for MongoLite on fast import processes.

Fixed in [V 0.12.2, Sept 06, 2021](https://discourse.getcockpit.com/t/v-0-12-2-sept-06-2021/2082)