Lets say you have a collection with a field called "primary_key",
{"primary_key":"1234", "name":"jimmy", "lastname":"page"}
and I have an index on "primary_key".
This collection has millions of rows, I want to see how expensive is to change primary_key for one of the records. Does it trigger a reindex of the entire table? or does it just reindex the changed record? in either case is that expensive to do?
Updating an indexed field in mongodb causes an update of the index (or indices if you have more than one) that use it. It does not "reindex". Shouldn't be all that expensive - effectively you will delete the old entry and insert a new one.
This document has a fair amount of detail on mongodb indexes:
http://docs.mongodb.org/master/MongoDB-indexes-guide.pdf
BTW, keep in mind that there is one special field, _id, that mongodb uses as it's primary key
_id
A field required in every MongoDB document. The _id field must have a unique value. You can think of the _id field as the document’s
primary key. If you create a new document without an _id field,
MongoDB automatically creates the field and assigns a unique BSON
ObjectId.
You cannot update the _id field.
Related
when I am inserting a document to MongoDB collection I get an error: E11000 duplicate key error collection
I would like to override the existing document with a new one.
Is there any way to force insert new data with the same _id field?
I am using go
You cannot insert two separate documents in MongoDB with the same _id field. This is stated in the documentation on document structure:
The field name _id is reserved for use as a primary key; its value must be unique in the collection, is immutable, and may be of any type other than an array.
What you're describing sounds more like an upsert, an operation that updates a document if it exists, and if it does not, inserts it instead. You could accomplish this by using updateOne and setting the upsert flag to true.
I'm have a huge documents in a collection. I want to remove auto generated Object Id (_id key) from all the documents and replace it with another field as a Primary key?
I don't understand is why is there a need for a default Object Id in first place?
In mongodb each document must be unique, so you need an unique field to be used as id. If you do not provide one, mongodb will provide one for you automatically. However, if you want to give custom ids for whichever reason (improve query performance being one of them), you can do it manually. Here goes my suggestions:
If you are inserting a new document, you can manually set the _id field like:
doc._id = "12312312" //(Or whichever function to generate id you have)
doc.save(...)
But when you already have a document in the database, you cannot modify it anymore. What you can do is to make a copy of the document, save a new document with the same data and erase the old one:
// Fetch the documents
docs = db.clients.find({})
docs.forEach((doc) => {
//For each field you copy the values
new_doc.field = doc.field
new_doc._id = //YOUR ID FUNCTION
// insert the document, using the new _id
db.clients.insert(new_doc)
// remove the document with the old _id
db.clients.remove({_id: doc._id})
}
This question is similar to the following one:
How update the _id of one MongoDB Document?
Hope my answer was helpful
It is not possible to remove the _id field.
From https://docs.mongodb.com/manual/core/document/#the-id-field:
In MongoDB, each document stored in a collection requires a unique _id field that acts as a primary key. If an inserted document omits the _id field, the MongoDB driver automatically generates an ObjectId for the _id field.
What you can do is name your primary key as _id.
Is there a way I can find the last inserted document and the field, i.e. _id or id such that I can increment and use when inserting a new document?
The issue is that I create my own id count, but I do not store this, now I've deleted records, I cannot seem to add new records because I am attempting to use the same id.
There is no way to check insertion order in MongoDB, because the database does not keep any metadata in the collections regading the documents.
If your _id field is generated server-side then you need to have a very good algorithm for this value in order to provide collision avoidance and uniqueness while at the same time following any sequential constraints that you might have.
Lets say you have a collection with a field called "primary_key",
{"primary_key":"1234", "name":"jimmy", "lastname":"page"}
and I have an index on "primary_key".
This collection has millions of rows, I want to see how expensive is to change primary_key for one of the records. Does it trigger a reindex of the entire table? or does it just reindex the changed record? in either case is that expensive to do?
Updating an indexed field in mongodb causes an update of the index (or indices if you have more than one) that use it. It does not "reindex". Shouldn't be all that expensive - effectively you will delete the old entry and insert a new one.
This document has a fair amount of detail on mongodb indexes:
http://docs.mongodb.org/master/MongoDB-indexes-guide.pdf
BTW, keep in mind that there is one special field, _id, that mongodb uses as it's primary key
_id
A field required in every MongoDB document. The _id field must have a unique value. You can think of the _id field as the document’s
primary key. If you create a new document without an _id field,
MongoDB automatically creates the field and assigns a unique BSON
ObjectId.
You cannot update the _id field.
I have a medium to large Mongo collection containing image metadata for >100k images. I am generating a UUID for each image generated and using it as the _id field in the imageMeta.insert() call.
I know for a fact that these _id's are unique, or at least as unique as I can expect from boost's UUID implementation, but as the collection grows larger, the time to insert a record has grown as well.
I feel like to ensure uniqueness of the _id field Mongo must be double-checking these against the other _ids in the database. How is this implemented, and how should I expect the insert time to grow wrt. to the collection size?
The _id field in mongo is required to be unique and indexed. When an insert is performed, all indexes in the collection are updated, so it's expected to see insert time increase with the number of indexes and/or documents. Namely, all collections have at least one index (on the _id field), but you've likely created indexes on fields that you frequently query, and those indexes also get updated on every insert (adding to the latency).
One way to reduce perceived database latency is to specify a write concern to your driver. Note that the default write concern prior to November 2012 was 'unacknowledged', but it has since been changed to 'acknowledged'.