Does mongo regex query have character limit, if the regex search string is more than that limit it throws error

Question

I am seeing mongo regex query not returning result when the regex searched string is very big, instead its throwing error. I have a scenario where I append lot of names to do a regex and thus my regex search string goes beyond 40000 characters. eg:

db.getCollection('collection').find(
    {"name":{"$regex" :"name1 | name2 | name3", "$options":"-i"}}
)

score 0 · Answer 1 · answered Oct 20 '16 at 06:04

0

Can you explain why you are doing this? The idea of a regex is to create a expression with which you match (multiple) value(s).

example expression:

name\d+

will match on all "namex" vales where x is a decimal.

The idea will be to create a single expression to fullfill your query requirement.

When you want to match on multiple string values you can use $and operator

answered Oct 20 '16 at 06:04

HoefMeistert

1,190
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17

I am doing a case insensitive search, query is as given below – user7045224 Oct 25 '16 at 07:08
db.collection.find( name: { "$regex":"red | white | blue|green " "$options": 'i')}) – user7045224 Oct 25 '16 at 07:10
the values string passed to regex can really grow very big and I am seeing mongo throwing exception when the string have characters above 37000 – user7045224 Oct 25 '16 at 07:12
This is not where regex is for... If you want to query use the $and operator. db.collection.find({$and : [ { name : "red"}, { name : "blue"} ]}) or the$in operator : db.collection.find({ name : { $in : [ "red", "white", "blue", "green" ]}}) you can create an array for it. It's required you store the value in lower case so the query is a success. As from MongoDB 3.4 there will be case insensitive indexes : https://jira.mongodb.org/browse/SERVER-90 – HoefMeistert Oct 25 '16 at 07:19
But my problem is data contains both upper and lower case (data coming from some legacy system)and I need a case insensitive search so I have to use regex with option i – user7045224 Oct 27 '16 at 03:51
@user7045224 like i said, this is not going to work with a regex. Atleast not with such a large pattern string. The most simple option is to store a lower/upper variant in your documents (easily done during save) and just use a find expression on it. If that's not implementable you can use a aggregation in which you lower/upper your value and match then. The main problem with the aggregation is that the match will not use a index.Or the last thing is to wait until the next release of mongoDB it will include caseinsensitive indexes. Hope it's clear. – HoefMeistert Oct 27 '16 at 05:24

score 0 · Answer 2 · edited Apr 25 '22 at 20:23

Yes, mongoDB regex has character limit, originates from perl regex limit. Because "MongoDB uses Perl compatible regular expressions (i.e. “PCRE” ) version 8.41 with UTF-8 support."MongoDB v3.2

You can see the limitation is 32764 characters:MongoDB add assert of regular expression length

I recently met this issue, and the solution was to use $in query operator instead. $in does not have characters limit. This suits my problem, since it was exact match rather than pattern matching in such long input case.

Does mongo regex query have character limit, if the regex search string is more than that limit it throws error

2 Answers2