Tag Archives: warehouse

Is Redshift outpacing Hadoop as the big data warehouse for startups?

redshift hadoop killer

More and more startups are looking at Redshift as a cheaper & faster solution for big data & analytics.

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Saggi Neumann posted a pretty good side-by-side comparison of Redshift & Hadoop and concluded they were tied based on your individual use case.

Meanwhile Bitly engineering concluded Redshift was much easier.

1. More agile

One thing pointed out by the bitly blog post, which I’ve seen countless times, is the slow iteration cycle. Write your map-reduce job, run, test, debug, then run on your cluster. Wait for it to return and you might feel like you’re submitting a stack of punched cards. LOL Resolve the errors that come back and then rerun on your cluster. Over & over & over again.

With Redshift you’re writing SQL, so your iterating through syntax errors quickly. What’s more since Redshift is a column-compressed database, you can do full table scans on columns without indexes.

What that means for you and me is that queries just run. And they run blazingly fast!

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2. Cheap

Redshift is pretty darn cheap.

Saggi’s article above quotes Redshift at $1000/TB/yr for reserved, and $3700/TB/yr for on-demand. This compared with a hadoop cluster at $5000/TB/yr.

But neither will come with spitting distance of the old-world of Oracle, where customers host big iron servers in their own datacenter, paying north of a million dollars between hardware & license costs. Amazon cloud FTW!

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3. Even faster

Airbnb’s nerds blog has a post showing it costing 25% of a Hadoop cluster, and getting 5x performance boost. That’s pretty darn impressive!

Flydata has done benchmarks showing 10x speedup.

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4. SQL Toolchains

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5. Limitations

o data loading

You load data into Redshift using the COPY command. This command reads flat files from S3 and dumps them into tables. It can be extremely fast if you do things in parallel. However getting your data into those flat files is up to you.

There are a few solutions to this.

– amazon data pipeline

This is Amazon’s own toolchain, which allows you to move data from RDS & other Amazon hosted data sources. Data pipeline does not move data realtime, but in batch. Also it doesn’t take care of schema changes so you have to do that manually.

I mentioned it in my 5 reasons to move data to Amazon Redshift

– Flydata service

Flydata is a service with a monthly subscription which will connect to your RDS database, and move the data into Redshift. This seems like a no brainer, and given the heft pricetag of thousands per month, you’d expect it to cover your bases.

In my experience there are a lot of problems & it still required a lot of administration. When schema changes happen, those have to be carefully applied on Redshift. What’s more there’s no silver bullet around the datatype differences.

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Flydata also makes use of the binary logs to replicate your data. Anything that doesn’t show up in the binary logs is going to cause you trouble. That includes when you do sql_log_bin=0 in the session, an SQL statement includes a no logging hint. Also watch out for replicate-ignore-db options in your my.cnf. But it also will fail if you use ON DELETE CASCADE. That’s because these downstream changes happen via Constraint in MySQL. But… drumroll please, Redshift doesn’t support ON DELETE CASCADE. In our case the child tables ended up with extra rows, and some queries broke.

– scripts such as Donors choose loader

Donors Choose has open sourced their nightly Redshift loader script. It appears to reload all data each night. This will nicely sidestep the ON DELETE CASCADE problem. As you grow though you may quickly hit a point where you can’t load the entire data set each night.

Their script sources from Postgres, though I’m interested to see if it can be modified for MySQL RDS.

– Tried & failed with Tungsten replicator

Theoretically Tungsten replicator can do the above. What’s more it seems like a tool custom made for such a use case. I tried for over a month to troubleshoot. I worked closely with the team to iron out bugs. I wrote wrestling with bears or how I tamed Tungsten replicator for MySQL and then I wrote a second article Tungsten replicator the good the bad & the ugly. Ultimately I did get some data moving between MySQL RDS & Redshift, however certain data clogged the system & it wouldn’t work for any length of time.

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o data types & character sets

There are a few things here to keep in mind. Redshift counts bytes, so if in mysql or some other database you had a varchar(5) it may be varchar(20) in Redshift. Even then I had cases where it still didn’t fit & I had to make the field bigger by 4.

I also ran into problems around string character encodings. According to the docs Redshift handles 4-byte UTF-8.

Redshift doesn’t support ARRAYs, BIT, BYTEA, DATE/TIME, ENUM, JSON and a bunch of others. So don’t go into it expecting full Postgres support.

What you will get are multibyte characters, numeric, character, datetime, boolean and some type conversion.

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o rebalancing

If and when you want to add nodes, expect some downtime. Yes theoretically the database is online while it’s shipping data to the new nodes & redistributing things, the latency can start to feel like an outage. What’s more it can easily push into the hours to do.

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