We investigation options to store and read a lot of immutable data (events) and I'd like some feedback on whether MongoDB would be a good fit.
Requirements:
We'll need to store about 10 events per seconds (but the rate will increase). Each event is small, about 1 Kb. Would it be fine to store all of these events in the same collection?
A really important requirement is that we need to be able to replay all events in order. I've read here that MongoDB have a limit of 32 Mb when sorting documents using cursors. For us it would be fine to read all data in insertion order (like a table scan) so an explicit sort might not be necessary? Are cursors the way to go and would they be able to fullfil this requirement?
If MongoDB would be a good fit for this there some configuration or setting one can tune to increase performance or reliability for immutable data?
This is very similar to storing logs: lots of writes, and the data is read back in order. Luckily the Mongo Site has a recipe for this:
https://docs.mongodb.org/ecosystem/use-cases/storing-log-data/
Regarding immutability of the data, that's not a problem for MongoDB.
Edit 2022-02-19:
Replacement link:
https://web.archive.org/web/20150917095005/docs.mongodb.org/ecosystem/use-cases/storing-log-data/
Snippet of content from page:
This document outlines the basic patterns and principles for using
MongoDB as a persistent storage engine for log data from servers and
other machine data.
Problem Servers generate a large number of events (i.e. logging,) that
contain useful information about their operation including errors,
warnings, and users behavior. By default, most servers, store these
data in plain text log files on their local file systems.
While plain-text logs are accessible and human-readable, they are
difficult to use, reference, and analyze without holistic systems for
aggregating and storing these data.
Solution The solution described below assumes that each server
generates events also consumes event data and that each server can
access the MongoDB instance. Furthermore, this design assumes that the
query rate for this logging data is substantially lower than common
for logging applications with a high-bandwidth event stream.
NOTE
This case assumes that you’re using a standard uncapped collection for
this event data, unless otherwise noted. See the section on capped
collections
Schema Design The schema for storing log data in MongoDB depends on
the format of the event data that you’re storing. For a simple
example, consider standard request logs in the combined format from
the Apache HTTP Server. A line from these logs may resemble the
following:
Related
I have used MongoDB but new to Cassandra. I have worked on applications which are using MongoDB and are not very large applications. Read and Write operations are not very much intensive. MongoDB worked well for me in that scenario. Now I am building a new application(w/ some feature like Stack Overflow[voting, totals views, suggestions, comments etc.]) with lots of Concurrent write operations on the same item into the database(in future!). So according to the information, I gathered via online, MongoDB is not the best choice (but Cassandra is). But the problem I am finding in Cassandra is Picking the right data model.
Construct Models around your queries. Not around relations and
objects.
I also looked at the solution of using Mongo + Redis. Is it efficient to update Mongo database first and then updating Redis DB for all multiple write requests for the same data item?
I want to verify which one will be the best to solve this issue Mongo + redis or Cassandra?
Any help would be highly appreciated.
Picking a database is very subjective. I'd say that modern MongoDB 3.2+ using the new WiredTiger Storage Engine handles concurrency pretty well.
When selecting a distributed NoSQL (or SQL) datastore, you can generally only pick two of these three:
Consistency (all nodes see the same data at the same time)
Availability (every request receives a response about whether it succeeded or failed)
Partition tolerance (the system continues to operate despite arbitrary partitioning due to network failures)
This is called the CAP Theorem.
MongoDB has C and P, Cassandra has A and P. Cassandra is also a Column-Oriented Database, and will take a bit of a different approach to storing and retrieving data than, say, MongoDB does (which is a Document-Oriented Database). The reality is that either database should be able to scale to your needs easily. I would worry about how well the data storage and retrieval semantics fit your application's data model, and how useful the features provided are.
Deciding which database is best for your app is highly subjective, and borders on an "opinion-based question" on Stack Overflow.
Using Redis as an LRU cache is definitely a component of an effective scaling strategy. The typical model is, when reading cacheable data, to first check if the data exists in the cache (Redis), and if it does not, to query it from the database, store the result in the cache, and return it. While maybe appropriate in some cases, it's not common to just write everything to both Redis and the database. You need to figure out what's cacheable and how long each cached item should live, and either cache it at read time as I explained above, or at write time.
It only depends on what your application is for. For extensive write apps it is way better to go with Cassandra
I have a problem...
I need to store a daily barrage of about 3,000 mid-sized XML documents (100 to 200 data elements).
The data is somewhat unstable in the sense that the schema changes from time to time and the changes are not announced with enough advance notice, but need to be dealt with retroactively on an emergency "hotfix" basis.
The consumption pattern for the data involves both a website and some simple analytics (some averages and pie charts).
MongoDB seems like a great solution except for one problem; it requires converting between XML and JSON. I would prefer to store the XML documents as they arrive, untouched, and shift any intelligent processing to the consumer of the data. That way any bugs in the data-loading code will not cause permanent damage. Bugs in the consumer(s) are always harmless since you can fix and re-run without permanent data loss.
I don't really need "massively parallel" processing capabilities. It's about 4GB of data which fits comfortably in a 64-bit server.
I have eliminated from consideration Cassandra (due to complex setup) and Couch DB (due to lack of familiar features such as indexing, which I will need initially due to my RDBMS ways of thinking).
So finally here's my actual question...
Is it worthwhile to look for a native XML database, which are not as mature as MongoDB, or should I bite the bullet and convert all the XML to JSON as it arrives and just use MongoDB?
You may have a look at BaseX, (Basex.org), with built in XQuery processor and Lucene text indexing.
That Data Volume is Small
If there is no need for parallel data processing, there is no need for Mongo DB. Especially if dealing with small data amounts like 4GB, the overhead of distributing work can easily get larger than the actual evaluation effort.
4GB / 60k nodes is not large of XML databases, either. After some time of getting into it you will realize XQuery as a great tool for XML document analysis.
Is it Really?
Or do you get daily 4GB and have to evaluate that and all data you already stored? Then you will get to some amount which you cannot store and process on one machine any more; and distributing work will get necessary. Not within days or weeks, but a year will already bring you 1TB.
Converting to JSON
How does you input look like? Does it adhere any schema or even resemble tabular data? MongoDB's capabilities for analyzing semi-structured are way worse than what XML databases provide. On the other hand, if you only want to pull a few fields on well-defined paths and you can analyze one input file after the other, Mongo DB probably will not suffer much.
Carrying XML into the Cloud
If you want to use both an XML database's capabilities in analyzing the data and some NoSQL's systems capabilities in distributing the work, you could run the database from that system.
BaseX is getting to the cloud with exactly the capabilities you need -- but it will probably still take some time for that feature to get production-ready.
Is there any sense to use mongodb in a system with great amount of entities (50+) connected to each other, for example in CRM. Any "success stories"?
There is a need of intensive writing and fast selection from high number of records for the some kind of analytics system.
It is definitely hard to provide a recommendation with such open question; however, you can analyze some of the advantages of MongoDB over other database, most likely you are considering Mongo as an alternative to a relational database like Oracle or SQL Server.
From http://mongodb.org you can see the main characteristics...
Document Oriented Storage: Which basically means you can have a single or multiple documents representing your data structures. One very important think here is that the schema is dynamic, that is you can add more attributes without having to change your database. Pretty useful for adding flexibility to your system.
Full index support: We wouldn't expect any less than full support for indices, right?
Replication and High availability; Sharding: Very critical elements for availability, disaster recovery, and to guarantee the
ability to grow with your system.
Querying: Again, pretty critical requirement. Need to make sure you account for the dynamic schema. You will need to consider in
your queries that some attributes are not defined for all documents
(remember dynamic schema?).
Map/Reduce: Very useful for
analytics. Recommended for aggregating large amounts of data.
Should be used offline, meaning, you don't run a live query against a
map/reduce function, otherwise you will be sitting for a while
waiting. But it is great to run batch analytics on your system.
GridFS: A great way of storing binary data. Automatically generates MD5's for your files, splits them in chunks, and can add
metadata. Your files will stay with your database.
Also, the Geolocation indices are great. You can define lon,lat attributes and do searches on those.
Now it is up to you to see if these features are good for your needs, or you rather stay with a well know relational system.
Before jumping into a solution you should experiment and build some prototypes. You will see very early what challenges you'll have in your design.
Hope this helps.
As part of my work we get approx 25TB worth log files annually, currently it been saved over an NFS based filesystem. Some are archived as in zipped/tar.gz while others reside in pure text format.
I am looking for alternatives of using an NFS based system. I looked at MongoDB, CouchDB. The fact that they are document oriented database seems to make it the right fit. However the log files content needs to be changed to JSON to be store into the DB. Something I am not willing to do. I need to retain the log files content as is.
As for usage we intend to put a small REST API and allow people to get file listing, latest files, and ability to get the file.
The proposed solutions/ideas need to be some form of distributed database or filesystem at application level where one can store log files and can scale horizontally effectively by adding more machines.
Ankur
Since you dont want queriying features, You can use apache hadoop.
I belive HDFS and HBase will be nice fit for this.
You can see lot of huge storage stories inside Hadoop powered by page
Take a look at Vertica, a columnar database supporting parallel processing and fast queries. Comcast used it to analyze about 15GB/day of SNMP data, running at an average rate of 46,000 samples per second, using five quad core HP Proliant servers. I heard some Comcast operations folks rave about Vertica a few weeks ago; they still really like it. It has some nice data compression techniques and "k-safety redundancy", so they could dispense with a SAN.
Update: One of the main advantages of a scalable analytics database approach is that you can do some pretty sophisticated, quasi-real time querying of the log. This might be really valuable for your ops team.
Have you tried looking at gluster? It is scalable, provides replication and many other features. It also gives you standard file operations so no need to implement another API layer.
http://www.gluster.org/
I would strongly disrecommend using a key/value or document based store for this data (mongo, cassandra, etc.). Use a file system. This is because the files are so large, and the access pattern is going to be linear scan. One thing problem that you will run into is retention. Most of the "NoSQL" storage systems use logical delete, which means that you have to compact your database to remove deleted rows. You'll also have a problem if your individual log records are small and you have to index each one of them - your index will be very large.
Put your data in HDFS with 2-3 way replication in 64 MB chunks in the same format that it's in now.
If you are to choose a document database:
On CouchDB you can use the _attachement API to attach the file as is to a document, the document itself could contain only metadata (like timestamp, locality and etc) for indexing. Then you will have a REST API for the documents and the attachments.
A similar approach is possible with Mongo's GridFs, but you would build the API yourself.
Also HDFS is a very nice choice.
I'm building a system that tracks and verifies ad impressions and clicks. This means that there are a lot of insert commands (about 90/second average, peaking at 250) and some read operations, but the focus is on performance and making it blazing-fast.
The system is currently on MongoDB, but I've been introduced to Cassandra and Redis since then. Would it be a good idea to go to one of these two solutions, rather than stay on MongoDB? Why or why not?
Thank you
For a harvesting solution like this, I would recommend a multi-stage approach. Redis is good at real time communication. Redis is designed as an in-memory key/value store and inherits some very nice benefits of being a memory database: O(1) list operations. For as long as there is RAM to use on a server, Redis will not slow down pushing to the end of your lists which is good when you need to insert items at such an extreme rate. Unfortunately, Redis can't operate with data sets larger than the amount of RAM you have (it only writes to disk, reading is for restarting the server or in case of a system crash) and scaling has to be done by you and your application. (A common way is to spread keys across numerous servers, which is implemented by some Redis drivers especially those for Ruby on Rails.) Redis also has support for simple publish/subscribe messenging, which can be useful at times as well.
In this scenario, Redis is "stage one." For each specific type of event you create a list in Redis with a unique name; for example we have "page viewed" and "link clicked." For simplicity we want to make sure the data in each list is the same structure; link clicked may have a user token, link name and URL, while the page viewed may only have the user token and URL. Your first concern is just getting the fact it happened and whatever absolutely neccesary data you need is pushed.
Next we have some simple processing workers that take this frantically inserted information off of Redis' hands, by asking it to take an item off the end of the list and hand it over. The worker can make any adjustments/deduplication/ID lookups needed to properly file the data and hand it off to a more permanent storage site. Fire up as many of these workers as you need to keep Redis' memory load bearable. You could write the workers in anything you wish (Node.js, C#, Java, ...) as long as it has a Redis driver (most web languages do now) and one for your desired storage (SQL, Mongo, etc.)
MongoDB is good at document storage. Unlike Redis it is able to deal with databases larger than RAM and it supports sharding/replication on it's own. An advantage of MongoDB over SQL-based options is that you don't have to have a predetermined schema, you're free to change the way data is stored however you want at any time.
I would, however, suggest Redis or Mongo for the "step one" phase of holding data for processing and use a traditional SQL setup (Postgres or MSSQL, perhaps) to store post-processed data. Tracking client behavior sounds like relational data to me, since you may want to go "Show me everyone who views this page" or "How many pages did this person view on this given day" or "What day had the most viewers in total?". There may be even more complex joins or queries for analytic purposes you come up with, and mature SQL solutions can do a lot of this filtering for you; NoSQL (Mongo or Redis specifically) can't do joins or complex queries across varied sets of data.
I currently work for a very large ad network and we write to flat files :)
I'm personally a Mongo fan, but frankly, Redis and Cassandra are unlikely to perform either better or worse. I mean, all you're doing is throwing stuff into memory and then flushing to disk in the background (both Mongo and Redis do this).
If you're looking for blazing fast speed, the other option is to keep several impressions in local memory and then flush them disk every minute or so. Of course, this is basically what Mongo and Redis do for you. Not a real compelling reason to move.
All three solutions (four if you count flat-files) will give you blazing fast writes. The non-relational (nosql) solutions will give you tunable fault-tolerance as well for the purposes of disaster recovery.
In terms of scale, our test environment, with only three MongoDB nodes, can handle 2-3k mixed transactions per second. At 8 nodes, we can handle 12k-15k mixed transactions per second. Cassandra can scale even higher. 250 reads is (or should be) no problem.
The more important question is, what do you want to do with this data? Operational reporting? Time-series analysis? Ad-hoc pattern analysis? real-time reporting?
MongoDB is a good option if you want the ability to do ad-hoc analysis based on multiple attributes within a collection. You can put up to 40 indexes on a collection, though the indexes will be stored in-memory, so watch for size. But the result is a flexible analytical solution.
Cassandra is a key-value store. You define a static column or set of columns that will act as your primary index right up front. All queries run against Cassandra should be tuned to this index. You can put a secondary on it, but that's about as far as it goes. You can, of course, use MapReduce to scan the store for non-key attribution, but it will be just that: a serial scan through the store. Cassandra also doesn't have the notion of "like" or regex operations on the server nodes. If you want to find all customers where the first name starts with "Alex", you'll have to scan through the entire collection, pull the first name out for each entry and run it through a client-side regex.
I'm not familiar enough with Redis to speak intelligently about it. Sorry.
If you are evaluating non-relational platforms, you might also want to consider CouchDB and Riak.
Hope this helps.
Just found this: http://blog.axant.it/archives/236
Quoting the most interesting part:
This second graph is about Redis RPUSH vs Mongo $PUSH vs Mongo insert, and I find this graph to be really interesting. Up to 5000 entries mongodb $push is faster even when compared to Redis RPUSH, then it becames incredibly slow, probably the mongodb array type has linear insertion time and so it becomes slower and slower. mongodb might gain a bit of performances by exposing a constant time insertion list type, but even with the linear time array type (which can guarantee constant time look-up) it has its applications for small sets of data.
I guess everything depends at least on data type and volume. Best advice probably would be to benchmark on your typical dataset and see yourself.
According to the Benchmarking Top NoSQL Databases (download here)
I recommend Cassandra.
If you have the choice (and need to move away from flat fies) I would go with Redis. Its blazingly fast, will comfortably handle the load you're talking about, but more importantly you won't have to manage the flushing/IO code. I understand its pretty straight forward but less code to manage is better than more.
You will also get horizontal scaling options with Redis that you may not get with file based caching.
I can get around 30k inserts/sec with MongoDB on a simple $350 Dell. If you only need around 2k inserts/sec, I would stick with MongoDB and shard it for scalability. Maybe also look into doing something with Node.js or something similar to make things more asynchronous.
The problem with inserts into databases is that they usually require writing to a random block on disk for each insert. What you want is something that only writes to disk every 10 inserts or so, ideally to sequential blocks.
Flat files are good. Summary statistics (eg total hits per page) can be obtained from flat files in a scalable manner using merge-sorty map-reducy type algorithms. It's not too hard to roll your own.
SQLite now supports Write Ahead Logging, which may also provide adequate performance.
I have hand-on experience with mongodb, couchdb and cassandra. I converted a lot of files to base64 string and insert these string into nosql.
mongodb is the fastest. cassandra is slowest. couchdb is slow too.
I think mysql would be much faster than all of them, but I didn't try mysql for my test case yet.