1

Hi All,

We have Oracle Star Schema. Can we migrate this Star Schema into Mongo DB ?

We have 1 Fact table and 15 dimension tables and almost all queries perform inner joins. Data in these tables are very huge.

Any pointers to blog and/or experience is highly appreciated.

2

‘Table of rows’ in SQL Databases equivalent to ‘Collection of documents’ in MongoDB. And Star Data Model can be represented as document with nested properties, like this:

{
  _id,
  totalA,
  totalB,
  dimentionA: {
    _id,
    dataA1,
    dataA2,
    ....
  },
  dimentionB: {
    _id,
    dataB1,
    dataB2,
    ....
  }
}

To put simply, your fact document will contain dimension documents as nested objects.
With this structure, you will not need to use any joins ($lookups), because every dimension is already joined to the fact data.

This scheme will be a perfect fit, only if the total size of such document will not exceed 16MB.

Check this OracleDB and MongoDB Comparison for more detailed overview.

3

Hi, I’ve put an example moving a star schema from Oracle to MongoDB, same model but using one Search Index to replace the many bitmap indexes:
https://dev.to/franckpachot/mongodb-with-search-indexes-queried-as-kimballs-star-schema-with-facts-and-dimensions-k1