Webinar: Migrating from RDBMS to MongoDB

Editor's Notes

• #3: HELLO! This is Buzz Moschetti at MongoDB, and welcome to today’s webinar entitled “Migrating If your travel plans today do not include exploring this topic then please exit the aircraft immediately and see an agent at the gate Otherwise – WELCOME ABOARD;
• #4: Some quick logistics. In the last 5 to 10 mins today, we will answer the most common questions that have appeared in the webinar.
• #5: Very briefly, a little bit about the person talking to you today over the net.
• #7: Why do this at all? This isn’t easy, mongoDB or otherwise. Changing your persistence engine is akin to a heart transplant. You don’t do this lightly – especially if you’ve got some semblance of a functioning heart! You would be looking at migration if you had some clear, measurable pains that prevented you from achieving your business / plaform value goals.
• #8: Not exhaustive list, and 2 isn’t the special number. Just 1 (like global replication) might be enough. But by the same token, you don’t want to “check off” ALL of the boxes because the ones you check off drive activities and design and cost of the migration
• #9: Let’s make it clear that this is about gaining value not reducing to zero the costs.
• #10: Maybe obvious, maybe not. When migrating to MongoDB, it is valuable and useful to examine the existing system stack overall.
• #11: The reason you want to examine the stack is because you can apply migration dollars in DIFFERENT parts of the stack, not JUST the persistor. This forms a set of possible migration options, each with a cost / value equation. And not all investments yield the same leveragable value. It is important at the very start to EXPLORE YOUR OPTIONS.
• #12: Of course, in addition, you’ll got training and certification, etc. etc.,
• #13: Value can come in form of performance, lower storage costs, increased resiliency
• #18: Lots of benefits of OO get traded away for ease of integration with ORM Business functionality ends up in the wrong place
• #19: As you move up stack it will cost you more to do less – a rewrite is a common cost you can make everything work together You can work out the boundary point – you can figure out where you need to stop changing – however sometimes the top three layers
• #20: Difficulty is subjective and depends on your team skill and experience.
• #21: Rewrite. Not as scary as it looks. Preserve GUIs and app logic and work your way DOWN instead of UP.
• #22: Things will change a bit – some wont change at all
• #23: Business needs to reset expectations SA need to embrace distributed DB capabilities at infraftructure level, rich shape ecosystem, etc. Developers can get much closer to the persisted form of data (typically not a big problem) Data Archiectc need to embrace Rich Shapes. DBAs, SysAdmin, and Secuirty clearly need to be adjusting and monitoring a diff set of knobs – but with the same end goal.
• #24: Should not be a surprise
• #25: Developers and Data Architects need to embrace rich shape design and understand tradeoffs Migrating to MongoDB likely has SOME amount of info architecture redesign. Pragmatic choices. On the right we see an example of a document with rich shape. It’s not just name:scalar paris; fields can be lists, including lists of complex structures. We call this embedding. Now, it’s not required when examining migration to embed everything but with MongoDB you have choices and certainly the “tightly bound” 1:n relationships are well-served by embedding.
• #26: Here is an example of a article / blog tracker. The RDBMS team did the theoretically good job by ensuring that 1:n relationships for tag, categories, and comments were set up in their own tables.. All too often especially for “small” things like tags and categories, designers take a shortcut and flatten out the data into the parent Article table, e.g. tag, tag2, and tag3. Or, to avoid running into the fieldN+1 problem, they create a single column a pack a semicolon delimited list into that column. In migrating to MongoDB, we’d probably keep the Article and User collections separate but the other entities are well-managed as list fields in the Article document. We could debate whether certain use cases would suggest moving Comment to its own collection but the point is at least you have choices. All this is indexable: Compound Indexes Unique indexes Array Indexes Text Indexes Geospatial indexes Sparse Indexes
• #27: Another important design consideration when migrating is adopting structured or nested data. Let’s explore the value. We start with BUYER first, middle, and last columns in the RDBMS. We choose to create a structure called consisting of first, last, and middle; in the example above, we’ll leave out middle name on purpose because we can. Inserting this in the RDBMS requires us to specify all the columns. In MongoDB, we save the entire structiure as field name buyer_name Fetching is symmetric in that we ask for buyer_name and get back the struct. In fairness, the symmetry is also preserved with RDBMS
• #28: Creating structures makes it easy to add new fields without changing other parts of the code that save and fetch.
• #29: But where the approach really shines is when you have several of the same kind of thing that you wish to manage consistently. Code and data both are clearer and more robustly changed.
• #30: Often legacy RDBMS schemas grow over time and end up like the above. In a greenfield environment you might create a 1:n relationship but our context here day is migration. But you might not. In any event, we now have to add TITLE to everything that seems to be a name…. This is a tedious and error-prone process.
• #31: By adopting structured data, you can take advantage of software to help build and manipulate these items. And MongoDB makes it easy to store, retrieve, and query them. And yes, it is possible to extract just parts of the nested structure via the MongoDB projection syntax, e.g. buyer_name.first
• #32: In the end, you have choice. And it is a spectrum of effort to value, not a single “do it or don’t do it” proposition. Data Architects and developers need to work together to find the sweet spot.
• #33: With all this talk about schema, it’s important to keep the value formula in mind. Sometimes, the pain relief provided in the infrastructure space – combined HA/DR, webscale read performance – might be enough to warrant migration LEGACY TABLES and all. In fact, along those lines, it is possible to take a multiphase approach to the migration where Day 1 go-live has a “suboptimal schema” but value is delivered. The benefit here is all parties from developer to operations can become comfortable running and modifying the new stack. Then, months later, the Phase II optimized schema is activated and the software switched over to use it instead.
• #34: Finally on roles, a brief note on DBAs We’ve heard people say “With MongoDB you don’t need DBAs” and that’s not true. You still need – in fact you WANT – DBAs but with MongoDB, you can create value by refocusing DBAs on the leveragable tasks and activities. In almost any technology, you’ll have a handful of experts. That’s a given. The next tier contains what should be highly leveragable tasks across many instances of databases. In fact, I’d assert that it is these tasks that most people believe are what most quote unquote “DBAs” should be doing. But very often, RDBMS DBAs end up performing a lot of non-leveragable upstack work like basic DDL maintenance. With MongoDB, many of those tasks can be performed by developers and level 1 ops who are already “at scale”; in other words, the staffing / responsibility profile for these people is already assumed to be narrowly scoped to 1 or 2 apps.
• #35: So now it’s time to actually get some data into MongoDB. In almost all migrations, at some point early on in development, you’ll want to bulk load old data into the new schema to experiment with performance, indexing, and managability. And you’ll probably want to turn that crank a few times. Especially at the start of an effort, you don’t need a robust operationalized, reconciliable incremental update and transfer system. Also, the operational profile and information architecture of the RDBMS system to be migrated might demand different approaches for extracting and massaging the data. So let’s take a look at some of our options.
• #36: If you can start with CR-delimited JSON (somehow) then mongoimport is a fine way to start. And the performance and tunability (i.e. threads and buffer sizes) in mongoimport v 2.8 has been significantly improved. Safety tip: JSON does not support Dates natively; thus, we use MongoDB type metadata conventions to direct mongoimport to treat strings as Dates as shown in green above. CR-delimited JSON is actually pretty powerful in its own right. Standard systems tools for counting lines and such work well on it and opern source tools like jq can be brought to bear on it. As you can imagine, it also compresses pretty well.
• #37: Of course, there is ETL, and the way you’d use it HERE is pretty much much the same way you’ve always designed, configured, and operated it. Pentaho & Informatica have partnership with MongoDB GUI based tools As powerful tools, they offer Mapping, workflow that transform, change schema along the way Can handle different sources Stable, robust, scalable migrations for large, complex data sets. Pentaho in particular embraces rich shape and has decent capability around “merging” RDBMS tables into more complex MongoDB embedded documents. But there are limitations in this space.
• #38: The mongoDB community is very large – we’re approaching 10 million downloads, Many people have built interesting tools that specialize in one thing or another and can be added to your bulk migration arsenal. Firehose is one example that specializes in loading and diagnostic functions but exposes them in a way to make it easy for you to incorporate into your apps should you desire to do so.
• #39: mongomtimport mimics most of the factory mongoimport functionality but permits user-defined and compiled parser and/or data handlers to be supplied on the command line. This gives you essentially unlimited functional capability that can operate on each document prior to being inserted into MongoDB.
• #40: Lastly, as an old time Perl hacker, I will shameless plug r2m.R2m brings the RAD and expressive power of perl together with a mongo loader framework to enable complex data manipulation and shape transformation. Because it uses the DBD/DBI framework as an input source, it can not only connect to all the RDBMSs but also Excel, web services, flatfiles, etc. There are literally dozens of DBD adapters you can use In this example, I am sure I could have changed the example above to fit in 3 lines instead of 6 but we’re going for clarity here. A flat structure of uppercased data is transformed into a nested structure of capitalized names. The iteration over the CONTACT table and other common logic like type conversion is handled by the framework.
• #41: R2m also makes it fairly easy to create 1:n embedding of Lists through the “join” function. And of course, in the end, with drivers for 10 languages including agile ones like python, perl, ruby, and javascript, you can always WRITE YOUR OWN.
• #42: Cutover is NOT something you think about one month before the event. It’s important and useful to think about system cutover very early in the migration effort because you have some options. Depending on your tolerance for downtime, failback, and investment in new code in the stack, you can adopt different approaches for making this happen.
• #43: This slide brought to you by the patient Technical Support Engineering staff at MongoDB, who have received many a frantic call about go-live in 24 hours and “something not working.” Build scripts that pound the DB and push the machine and disks to the max. Identify your first bottlenecks that lie ahead of your stated performance requirements. Remember: You don’t have a lot of experience and years worth of built-in assumptions about how this system SHOULD perform.
• #44: PROS: Very conservative; little or no direct impact on live old stack In fact, you can blur migrate and rewrite here. Oftimes an entire copy of the stack is made so breaking changes can be introduced and dealt with across the stack without a giant coordinated release. CONS That Sunday is going to be a doozie! Unclear what failback looks like Variation: Partition data in some way (region? User sets?) and run dual live ; requires app topside changes to put user onto the right stack
• #45: PROS: Gets a DAL in there which is good. Can periodically test thru special pathways into staged MongoDB stack Reasonable failback CONS: You may not want / be able to engineer in a DAL. Last flush of activity might be longer than minutes
• #46: PROS: Continuous incremental migration. CONS Some environments might not tolerate performance hit of copy/sync Still a Day 1 migration event when new stack goes live NEEDS VERY GOOD TESTING
• #47: You don’t have to go at this alone.
• #48: Migration has worked and has produced value for a number of projects Edmunds – Billing, online advertising, user data (Oracle) Metlife – Single view of 100M+ customers and 70 systems in 90 days Cisco - Analytics, Social Networking (Various) Salesforce – Real time analytics (Various) Expedia – Special travel offers in real time Adobe – Digital experience management platform Shutterfly – Developed nearly a dozen projects on MongoDB storing more than 20TB data (Oracle) Need for Rich shape management and legacy pain of RDMS produced value. Craigslist – Archive data migration (MySQL) MTV - Centralized Content Management (Various) (Large broker / dealer did reference data conversion which led to direct reduction in cost of 10mm and follow on saves of 30mm)
• #49: On behalf of all of us at MongoDB , thank you for attending this webinar! I hope what you saw and heard today gave you some insight and clues into what you might face in your own migration efforts. Remember you can always reach out to us at MongoDB for guidance. So with that, Happy Holidays! Code well, and be well!