Using Apache Spark to serve real time web services queries - web-services

We have a use case, where we are downloading large volumes (order of 100 gigabytes per day) of data from hundreds of data sources, massaging and processing this data and then exposing this data to our customers via RESTful API. Today the base data size is ca. 20TB and expected to grow heavily in the future.
For the massaging/processing part, we believe spark can be a very good choice for us. Now for exposing processed/massaged data through an API, one option is to store processed data to a read only database like ElephantDB and make web services to talk to ElephantDB (at least this is how Nathan has proposed in his Big Data book). I was just wondering what would be the implication of we make web services implementation to use SparkSQL to access processed data from Spark. What could be the architecture/design dangers in this case?
Every body is talking about Spark is fast and what not and using SparkSQL for interactive queries. But is it already in a stage to serve large volume of web services queries via SparkSQL where we have very strict SLA for latency serve hundreds and thousands of web services requests per second? If Apache Spark could handle this, we could avoid maintaining yet another system like ElephantDB or Cassandra or what not.
Would like to hear from the experts on this board.

If the results are stored in files, you have no indexes, and SparkSQL also doesn't create indexes. The only thing that can be somewhat fast is reading columns from Parquet files and caching tables.
But in general it's not a good use case to use SparkSQL to serve web requests simply because Spark wasn't made for that.

So you're batch processing the raw data, yes?
The ideal way would be to store the outcome on a key-value format, as you mention with ElephandDB, and also project Voldemort has been shown to be a good fit as read-only storage.
I recommend you to read this article (combining batch and realtime layers) by Nathan Marz: How to beat the CAP theorem
It has however been questioned by Jay Kreps in his article Questioning the Lambda Architecture. The main concern (with the lambda architecture) is that there is problematic to maintain the "same" system logic in different distributed systems to produce the same result.
But since you are using Spark, you can use the same logic with Spark Streaming. Which was not "in the market" when Nathan Marz and Jay Kreps wrote their articles.
You can still use SparkSQL to query the raw data interactively, but since Spark was first implemented as scheduled batch jobs, this will not be the perfect use case. But as you've probably noticed, is that it takes some time to submit spark jobs, this is an overhead that "kills" the idea of fast queries.
Please look into github.com/spark-jobserver/spark-jobserver, the job-server supports sub-second low-latency jobs via long-running job contexts. And can share Spark RDDs between different jobs, which can be proved to be very optimized for different interactive logic on the same dataset. Combine machine learning result and ad-hoc (SparkSQL) queries via HTTP requests. Read more about spark job-server, there are some talks about it online on different Spark Summits.

Related

Microservice architecture for ETL

I am redesigning a small monolith ETL software written in Python. I find a microservice architecture suitable as it will give us the flexibility to use different technologies if needed (Python is not the nicest language for enterprise software in my opinion). So if we had three microservices (call them Extract, Transform, Load), we could use Java for Transform microservice in the future.
The problem is, it is not feasible here to pass the result of a service call in an API response (say HTTP). The output from Extract is going to be gigabytes of data.
One idea is to call Extract and have it store the results in a database (which is really what that module is doing in the monolith, so easy to implement). In this case, the service will return only a yes/no response (was the process successful or not).
I was wondering if there were a better way to approach this. What would be a better architecture? Is what I'm proposing reasonable?
If your ETL process works on individual records (some parallelize-able units of computation), then there are a lot of options you could go with, here are a few:
Messaging System-based
You could base your processing around a messaging system, like Apache Kafka. It requires a careful setup and configuration (depending on durability, availability and scalability requirements of your specific use-cases), but may give you a better fit than a relational db.
In this case, the ETL steps would work completely independently, and just consume some topics, produce into some other topics. Those other topics are then picked up by the next step, etc. There would be no direct communication (calls) between the E/T/L steps.
It's a clean and easy to understand solution, with independent components.
Off-the-shelf processing solutions
There are a couple of OTS solutions for data processing/computation and transformation: Apache Flink, Apache Storm, Apache Spark.
Although these solutions would obviously confine you to one particular technology, they may be better than building a similar system from scratch.
Non-persistent
If the actual data is streaming/record-based, and it is not required to persist the results between steps, you could just get away with long-polling the HTTP output of the previous step.
You say it is just too much data, but that data doesn't have to go to the database (if it's not required), and could just go to the next step instead. If the data is produced continuously (not everything in one batch), on the same local network, I don't think this would be a problem.
This would be technically very easy to do, very simple to validate and monitor.
I would suggest you to have a look into the Apache flink, It is very similar to what big sized enterprise apps like informatica, talend and data stage mappings but it process in a smaller scale but repetitively. It actually helps you to compute and transform the stuff on the fly/as they arrive and then store/load into a file/db.
The current infra we have with flink process close 28.5GB per every 4 hours and it just works. In the initial days, we had to run our daily batch and the flink stream to ensure both of them are producing consistent results and eventually most of the streams were left active and the daily batches were retired gradually.
Hope it helps someone.
There's none preventing you to have an SFTP server containing CSV or database storing the results. You can do whatever make senses. Using messaging to pass gigabytes of data, or streaming through HTTP may or may not make senses for your case.
This is an interesting problem. The best solution for this could be Reactive Spring Boot. You can have your Extract service to be as a Reactive Spring Boot app and instead of sending GBs of data, stream the data to the required service.
Now you might be wondering that while streaming, it might hold on the working thread. The answer is NO. IT works at the OS level. It doesn't hold up any request thread to stream the results. That's the beauty of the Reactive Spring Boot.
Go through this and explore
https://spring.io/blog/2016/07/28/reactive-programming-with-spring-5-0-m1

AWS Redshift vs Snowflake use cases

I was wondering if anyone has used both AWS Redshift and Snowflake and use cases where one is better . I have used Redshift but recently someone suggested Snowflake as a good alternative . My use case is basically retail marketing data that will be used by handful of analysts who are not terribly SQL savvy and will most likely have reporting tool on top
Redshift is a good product, but it is hard to think of a use case where it is better than Snowflake. Here are some reasons why Snowflake is better:
The admin console is brilliant, Redshift has none.
Scale-up/down happens in seconds to minutes, Redshift takes minutes to hours.
The documentation for both products is good, but Snowflake is better laid
out and more accessible.
You need to know less "secret sauce" to make Snowflake work well. On Redshift you need to know and understand the performance impacts of things like distribution keys and sort keys, at a minimum.
The load processes for Snowflake are more elegant than Redshift. Redshift assumes that your data is in S3 already. Snowflake supports S3, but has extensions to JDBC, ODBC and dbAPI that really simplify and secure the ingestion process.
Snowflake has great support for in-database JSON, and is rapidly enhancing its XML. Redshift has a more complex approach to JSON, and recommends against it for all but smaller use cases, and does not support XML.
I can only think of two cases which Redshift wins hands-down. One is geographic availability, as Redshift is available in far more locations than Snowflake, which can make a difference in data transfer and statement submission times. The other is the ability to submit a batch of multiple statements. Snowflake can only accept one statement at a time, and that can slow down your batches if they comprise many statements, especially if you are on another continent to your server.
At Ajilius our developers use Redshift, Snowflake and Azure SQL Data Warehouse on a daily basis; and we have customers on all three platforms. Even with that choice, every developer prefers Snowflake as their go-to cloud DW.
I evaluated both Redshift(Redshfit spectrum with S3) and SnowFlake.
In my poc, snowFlake is way way better than Redshift. SnowFlake integrates well with Relational/NOSQL data. No upfront index or partition key required. It works amazing without worrying about what way to access the day.
Redshift is very limited and no json support. Its hard to understand the partition. You have to do lot of work to get something done. No json support. You can use redshift specturm as a bandaid to access S3. Good luck with partioning upfront. Once you created partition in S3 bucket, you are done with that and no way to change until unless you redo process all data again to new structue. You will end up sending time to fix these issues instead of working on fixing real business problems.
Its like comparing Smartphone vs Morse code mechine. Redshift is like morse code kind of implementation and its not for mordern development
We recently switched from Redshift to Snowflake for the following reasons:
Real-time data syncing
Handling of concurrent queries
Minimizing of database administration
Providing different amounts of computing power to different Looker users
A more in-depth writeup can be found on our data blog.
I evaluated Redshift and Snowflake, and a little bit of Athena and Spectrum as well. The latter two were non-starters in cases where we had big joins, as they would run out of memory. For Redshift, I could actually get a better price to performance ratio for a couple reasons:
allows me to choose a distribution key which is huge for co-located joins
allows for extreme discounts on three year reserved pricing, so much so that you can really upsize your compute at a reasonable cost
I could get better performance in most cases with Redshift, but it requires good MPP knowledge to setup the physical schema properly. The cost of expertise and complexity offsets some of the product cost.
Redshift stores JSON in a VARCHAR column. That can cause problems (OOM) when querying a subset of JSON elements across large tables, where the VARCHAR column is sized too big. In our case we had to define the VARCHAR as extremely large to accommodate a few records that had very large JSON documents.
Snowflake functionality is amazing, including:
ability to clone objects
deep functionality in handling JSON data
snowpipe for low maintenance loading, auto scaling loads, trickle updates
streams & tasks for home grown ETL
ability to scale storage and compute separately
ability to scale compute within a minute, requiring no data migration
and many more
One thing that I would caution about Snowflake is that one might be tempted to hire less skilled developers/DBAs to run the system. Performance in a bad schema design can be worked around using a huge compute cluster, but that may not be the best bang for the buck. Regardless, the functionality in Snowflake is amazing.

What is the different between AWS Elasticsearch and AWS Redshift

I read the document that both for data analysis and in cluster structure but I don't understand what use case different.
Amazon Elasticsearch is a popular open-source search and analytics engine for use cases such as log analytics, real-time application monitoring, and clickstream analytics.Amazon Elasticsearch
Amazon Redshift is a fully managed, petabyte-scale data warehouse service in the cloud. You can start with just a few hundred gigabytes of data and scale to a petabyte or more. Amazon Redshift
Amazon Redshift is a hosted data warehouse product, while Amazon Elasticsearch is a hosted ElasticSearch cluster.
Redshift is based on PostgreSQL and (afaik) mostly used for BI purpuses and other compute-intensive jobs, the Amazon Elasticsearch is an out-of-the-box ElasticSearch managed cluster (which you cannot use to run SQL queries, since ES is a NoSQL database).
Both Amazon Redshift and Amazon ES are managed services, which means you don't need to do anything in order to manage your servers (this is what you pay for). Using the AWS Console you can add new cluster and you don't need to run any commands on order to install any software - you just need to choose which server to run your cluster on (number of nodes, disk, ram, etc).
If you are not familiar with ElasticSearch you should check their website.
Edit: It is now possible to write SQL queries on ElasticSearch: SQL Support for AWS ElasticSearch
I agree with #IMSoP's assertions above...
To compare the two is like comparing an elephant and a tiger - you're not really asking the right question quite yet.
What you should really be asking is - what are my requirements for my use cases to best fulfill my stakeholder / customer needs, first, and then which data storage technology best aligns with my requirements second...
To be clear - Whether speaking of AWS ElasticSearch Service, or FOSS / Enterprise ElasticSearch (which have signifficant differences, between, even) - ElasticSearch is NOT a Relational Database (RDBMS), nor is it quite a NoSQL (Document Store) Database, either...
ElasticSearch is a Search Engine / Index. It does some things very well, for very specific use cases, however unlike RDBMS data models most signifficantly, ElasticSearch or NoSQL are not going to provide you with FULL ACID Compliance, or Transactional Statement Processing, so if your use case prioritizes data integrity, constrainability, reliability, audit ability, regulatory compliance, recover ability (to Point in Time, even), and normalization of data model for performance and least repetition of data while providing deep cardinality and enforcing model constraints for optimal integrity, "NoSQL and Elastic are not the Droids you're looking for..." and you should be implementing a RDBMS solution. As already mentioned, the AWS Redshift Service is based on PostgreSQL - which is one of the most popular OpenSource RDBMS flavors out there, just offered by AWS as a fully managed solution / service for their customers.
Elastic falls between RDBMS and NoSQL categories, as it is a Search Engine / Index that works most optimally with "single index" type use cases, where A LOT of content is indexed all at once and those documents aren't updated very frequently after the initial bulk indexing,but perhaps the most important thing I could stress is that in my experience it typically does not scale very cost effectively (even managed cluster services) if you want your clusters to perform well, not degrade over time, retain large historical datasets, and remain highly available for your consumers - and for most will likely become cost PROHIBITIVE VERY fast. That said, Elastic Search DOES still have very optimal use cases, so is always worth evaluating against your unique requirements - just keep scalability and cost in mind while doing so.
Lastly let's call NoSQL what it is, a Document Store that stores collections of documents (most often in JSON format) and while they also do indexing, offer some semblance of an Authentication and Authorization model, provide CRUD operability (or even SQL support nowadays, which makes the career Enterprise Data Engineer in me giggle, that SQL is now the preferred means of querying data from their NoSQL instances! :D )- Still NOT a traditional database, likely won't provide you with much control over your data's integrity - BUT that is precisely what "NoSQL" Document Stores were designed to work best for - UNSTRUCTURED DATA - where you may not always know what your data model is going to look like from the start, or your use case prioritizes data model flexibility over enforcing data integrity in general (non mission critical data). Last - while most modern NoSQL Document Stores may have SOME features that appear on the surface to resemble RDBMS, I am not aware of ANY in that category at current that could claim to offer all that a relational database does, with Oracle MySQL's DocumentStore being probably the best of both worlds in my opinion (and not just because I've worked with it every day for the last decade, either...).
So - I hope Developers with similar questions come across this thread, and after reading are much better informed to make the most optimal design decisions for their use cases - because if we're all being honest with ourselves - everything we do in our profession is about data - either generating it, transporting it, rendering it, transforming it....it all starts and ends with data, and making the most optimal data storage decisions for your applications will literally define the rest of your project!
Cheers!
This strikes me as like asking "What is the difference between apples and oranges? I've heard they're both types of fruit."
AWS has an overview of the analytics products they offer, which at the time of writing lists 21 different services. They also have a list of database products which includes Redshift and 10 others. There's no particularly obvious reason why these two should be compared, and the others on both pages ignored.
There is inevitably a lot of overlap between the capabilities of these tools, so there is no way to write an exhaustive list of use cases for each. Their strengths and weaknesses, and the other tools they integrate easily with, will change over time, and some differences are a matter of "taste" or "style".
Regarding the two picked out in the question:
Elasticsearch is a product built by elastic.co, which AWS can manage the installation and configuration for. As its name suggests, its core functionality is based around search - it can be used to build a flexible but fast product search for an e-commerce site, for instance. It's also commonly used along with other tools to search and aggregate logs and monitoring data.
Redshift is a database system built by AWS, based on PostgreSQL but optimised for extremely large data sets. It is designed for "data warehouse" applications, where you want to write complex logical queries against the data, like "how many people in each city bought both a toothbrush and toothpaste, this year compared to last year".
Rather than trying to make an abstract comparison of all the different services available, it makes more sense to start from the use case which you actually have, and see which tool best fits that need.

Redshift as a Web App Backend?

I am building an application (using Django's ORM) that will ingest a lot of events, let's say 50/s (1-2k per msg). Initially some "real time" processing and monitoring of the events is in scope so I'll be using redis to keep some of that data to make decisions, expunging them when it makes sense. I was going to persist all of the entities, including events in Postgres for "at rest" storage for now.
In the future I will need "analytical" capability for dashboards and other features. I want to use Amazon Redshift for this. I considered just going straight for Redshift and skipping Postgres. But I also see folks say that it should play more of a passive role. Maybe I could keep a window of data in the SQL backend and archive to Redshift regularly.
My question is:
Is it even normal to use something like Redshift as a backend for web applications or does it typically play more of a passive role? If not is it realistic to think I can scale the Postgres enough for the event data to start with only that? Also if not, does the "window of data and archival" method make sense?
EDIT Here are some things I've seen before writing the post:
Some say "yes go for it" regarding the should I use Redshift for this question.
Some say "eh not performant enough for most web apps" and support the front it with a postgres database camp.
Redshift (ParAccel) is an OLAP-optimised DB, based on a fork of a very old version of PostgreSQL.
It's good at parallelised read-mostly queries across lots of data. It's bad at many small transactions, especially many small write transactions as seen in typical OLTP workloads.
You're partway in between. If you don't mind a data loss window, then you could reasonably accumulate data points and have a writer thread or two write batches of them to Redshift in decent sized transactions.
If you can't afford any data loss window and expect to be processing 50+ TPS, then don't consider using Redshift directly. The round-trip costs alone would be horrifying. Use a local database - or even a file based append-only journal that you periodically rotate. Then periodically upload new data to Redshift for analysis.
A few other good reasons you probably shouldn't use Redshift directly:
OLAP DBs with column store designs often work best with star schemas or similar structures. Such schemas are slow and inefficient for OLTP workloads as inserts and updates touch many tables, but they make querying the data along various axes for analysis much more efficient.
Using an ORM to talk to an OLAP DB is asking for trouble. ORMs are quite bad enough on OLTP-optimised DBs, with their unfortunate tendency toward n+1 SELECTs and/or wasteful chained left joins, tendency to do many small inserts instead of a few big ones, etc. This will be even worse on most OLAP-optimised DBs.
Redshift is based on a painfully old PostgreSQL with a bunch of limitations and incompatibilities. Code written for normal PostgreSQL may not work with it.
Personally I'd avoid an ORM entirely for this - I'd just accumulate data locally in an SQLite or a local PostgreSQL or something, sending multi-valued INSERTs or using PostgreSQL's COPY to load chunks of data as I received it from an in-memory buffer. Then I'd use appropriate ETL tools to periodically transform the data from the local DB and merge it with what was already on the analytics server.
Now forget everything I just said and go do some benchmarks with a simulation of your app's workload. That's the only really useful way to tell.
In addition to Redshift's slow transaction processing (by modern DB standards) there's another big challenge:
Redshift only supports serializable transaction isolation, most likely as a compromise to support ACID transactions while also optimizing for parallel OLAP mostly-read workload.
That can result in all kinds of concurrency-related failures that would not have been failures on typical DB that support read-committed isolation by default.

Service in front of Hadoop

I would like to expose a web service in front of Hadoop, that is used to forward data to Hadoop ecosystem. I have two branches in Hadoop, slower, that works on whole data periodically, and fast, that does some computation on every input, and stores the data for periodical job. But the user does not see the slower branch, and has a feeling that only the fast job is done, not knowing for the slower job that runs on data aggregated during time.
How to organize my architecture best? I am new to Hadoop architecture, I read about Oozie, and have a feeling that it can help me to some point. But I don't know how to connect the service with Hadoop, how to pass the data through service, since Hadoop works primarily on files, and is distributed system.
Data should get into system in a streaming fashion. There should be "real time" branch, that works with individual values that get into system, and they would also be accumulated for periodic batch processing.
Any help would be great, thanks.
You might want to look into hue . This provides a set of web front-ends: there's one for HDFS (the filesystem) where you can upload files; there are means to track jobs too.
If you aim more regular and automated putting of files into HDFS, please elaborate your question further: where and what is the data initially (logs? db? bunch of gzipped csv-s?), what should trigger retrieval/
One can as well use API-s to deal with the filesystem and to track jobs.
As for what oozie concerns, this is more of an orchestrating tool, use it to organize related jobs into workflows.