Hadoop
Discussion of Hadoop. Related subjects include:
Teradata SQL-H
As vendors so often do, Teradata has caused itself some naming confusion. SQL-H was introduced as a facility of Teradata Aster, to complement SQL-MR.* But while SQL-MR is in essence a set of SQL extensions, SQL-H is not. Rather, SQL-H is a transparency interface that makes Hadoop data responsive to the same code that would work on Teradata Aster …
*Speaking of confusion — Teradata Aster seems to use the spellings SQL/MR and SQL-MR interchangeably.
… except that now there’s also a SQL-H for regular Teradata systems as well. While it has the same general features and benefits as SQL-H for Teradata Aster, the details are different, since the underlying systems are.
I hope that’s clear. 🙂
| Categories: Data integration and middleware, Data warehousing, Emulation, transparency, portability, Hadoop, SQL/Hadoop integration, Teradata | 2 Comments |
Some notes on new-era data management, March 31, 2013
Hmm. I probably should have broken this out as three posts rather than one after all. Sorry about that.
Performance confusion
Discussions of DBMS performance are always odd, for starters because:
- Workloads and use cases vary greatly.
- In particular, benchmarks such as the YCSB or TPC-H aren’t very helpful.
But in NoSQL/NewSQL short-request processing performance claims seem particularly confused. Reasons include but are not limited to:
- It’s common for databases or at least working sets to be entirely in RAM — but it’s not always required.
- Consistency and durability models vary. What’s more, in some systems — e.g. MongoDB — there’s considerable flexibility as to which model you use.
- In particular, there’s an increasingly common choice in which data is written synchronously to RAM on 2 or more servers, then asynchronously to disk on each of them. Performance in these cases can be quite different from when all writes need to be committed to disk. Of course, you need sufficient disk I/O to keep up, so SSDs (Solid-State Drives) can come in handy.
- Many workloads are inherently single node (replication aside). Others are not.
MongoDB and 10gen
I caught up with Ron Avnur at 10gen. Technical highlights included: Read more
Platfora at the time of first GA
Well-resourced Silicon Valley start-ups typically announce their existence multiple times. Company formation, angel funding, Series A funding, Series B funding, company launch, product beta, and product general availability may not be 7 different “news events”, but they’re apt to be at least 3-4. Platfora, no exception to this rule, is hitting general availability today, and in connection with that I learned a bit more about what they are up to.
In simplest terms, Platfora offers exploratory business intelligence against Hadoop-based data. As per last weekend’s post about exploratory BI, a key requirement is speed; and so far as I can tell, any technological innovation Platfora offers relates to the need for speed. Specifically, I drilled into Platfora’s performance architecture on the query processing side (and associated data movement); Platfora also brags of rendering 100s of 1000s of “marks” quickly in HTML5 visualizations, but I haven’t a clue as to whether that’s much of an accomplishment in itself.
Platfora’s marketing suggests it obviates the need for a data warehouse at all; for most enterprises, of course, that is a great exaggeration. But another dubious aspect of Platfora marketing actually serves to understate the product’s merits — Platfora claims to have an “in-memory” product, when what’s really the case is that Platfora’s memory-centric technology uses both RAM and disk to manage larger data marts than could reasonably be fit into RAM alone. Expanding on what I wrote about Platfora when it de-stealthed: Read more
DBMS development and other subjects
The cardinal rules of DBMS development
Rule 1: Developing a good DBMS requires 5-7 years and tens of millions of dollars.
That’s if things go extremely well.
Rule 2: You aren’t an exception to Rule 1.
In particular:
- Concurrent workloads benchmarked in the lab are poor predictors of concurrent performance in real life.
- Mixed workload management is harder than you’re assuming it is.
- Those minor edge cases in which your Version 1 product works poorly aren’t minor after all.
DBMS with Hadoop underpinnings …
… aren’t exceptions to the cardinal rules of DBMS development. That applies to Impala (Cloudera), Stinger (Hortonworks), and Hadapt, among others. Fortunately, the relevant vendors seem to be well aware of this fact. Read more
Dataset management
I coined a new term, dataset management, for my clients at Revelytix, which they indeed adopted to describe what they do. It would also apply to the recently released Cloudera Navigator. To a first approximation, you may think of dataset management as either or both:
- Metadata management in a structured-file context.
- Lineage/provenance, auditing, and similar stuff.
Why not just say “metadata management”? First, the Revelytix guys have long been in variants of that business, and they’re tired of the responses they get when they use the term. 🙂 Second, “metadata” could apply either to data about the file or to data about the data structures in the file or perhaps to data about data in the file, making “metadata” an even more confusing term in this context than in others.
My idea for the term dataset is to connote more grandeur than would be implied by the term “table”, but less than one might assume for a whole “database”. I.e.:
- A dataset contains all the information about something. This makes it a bigger deal than a mere table, which could be meaningless outside the context of a database.
- But the totality of information in a “dataset” could be less comprehensive than what we’d expect in a whole “database”.
As for the specific products, both of which you might want to check out:
- Cloudera Navigator:
- Is one product from a leading Hadoop company.
- Assumes you use Cloudera’s flavor of Hadoop.
- Is generally available.
- Starts with auditing (lineage coming soon).
- Revelytix Loom:
- Is the main product of a small metadata management company.
- Is distro-agnostic.
- Is in beta.
- Already does lineage.
| Categories: Cloudera, Hadoop | 6 Comments |
Hadoop execution enhancements
Hadoop 2.0/YARN is the first big step in evolving Hadoop beyond a strict Map/Reduce paradigm, in that it at least allows for the possibility of non- or beyond-MapReduce processing engines. While YARN didn’t meet its target of general availability around year-end 2012, Arun Murthy of Hortonworks told me recently that:
- Yahoo is a big YARN user.
- There are other — paying — YARN users.
- YARN general availability is now targeted for well before the end of 2013.
Arun further told me about Tez, the next-generation Hadoop processing engine he’s working on, which he also discussed in a recent blog post:
With the emergence of Apache Hadoop YARN as the basis of next generation data-processing architectures, there is a strong need for an application which can execute a complex DAG [Directed Acyclic Graph] of tasks which can then be shared by Apache Pig, Apache Hive, Cascading and others. The constrained DAG expressible in MapReduce (one set of maps followed by one set of reduces) often results in multiple MapReduce jobs which harm latency for short queries (overhead of launching multiple jobs) and throughput for large-scale queries (too much overhead for materializing intermediate job outputs to the filesystem). With Tez, we introduce a more expressive DAG of tasks, within a single application or job, that is better aligned with the required processing task – thus, for e.g., any given SQL query can be expressed as a single job using Tez.
This is similar to the approach of BDAS Spark:
Rather than being restricted to Maps and Reduces, Spark has more numerous primitive operations, including map, reduce, sample, join, and group-by. You can do these more or less in any order.
although Tez won’t match Spark’s richer list of primitive operations.
More specifically, there will be six primitive Tez operations:
- HDFS (Hadoop Distributed File System) input and output.
- Sorting on input and output (I’m not sure why that’s two operations rather than one).
- Shuffling of input and output (ditto).
A Map step would compound HDFS input, output sorting, and output shuffling; a Reduce step compounds — you guessed it! — input sorting, input shuffling, and HDFS output.
I can’t think of much in the way of algorithms that would be logically impossible in MapReduce yet possible in Tez. Rather, the main point of Tez seems to be performance, performance consistency, response-time consistency, and all that good stuff. Specific advantages that Arun and I talked about included:
- The requirement for materializing (onto disk) intermediate results that you don’t want to is gone. (Yay!)
- Hadoop jobs will step on each other’s toes less. Instead of Maps and Reduces from unrelated jobs getting interleaved, all the operations from a single job will by default be executed in one chunk. (Even so, I see no reason to expect early releases of Tez to do a great job on highly concurrent mixed workload management.)
- Added granularity brings opportunities for additional performance enhancements, for example in the area of sorting. (Arun loves sorts.)
| Categories: Databricks, Spark and BDAS, Hadoop, Hortonworks, MapReduce, Workload management, Yahoo | 14 Comments |
Open source strategies
From time to time I advise a software vendor on how, whether, or to what extent it should offer its technology in open source. In summary, I believe:
- The formal differences between “open source” and “closed source” strategies are of secondary importance.
- The attitudinal and emotional differences between “open source” and “closed source” approaches can be large.
- A pure closed source strategy can make sense.
- A closed source strategy with important open source aspects can make sense.
- A pure open source strategy will only rarely win.
Here’s why.
An “open source software” business model and strategy might include:
- Software given away for free.
- Demand generation to encourage people to use the free version of the software.
- Subscription pricing for additional proprietary software and support.
- Direct sales, and further marketing, to encourage users of the free stuff to upgrade to a paid version.
A “closed source software” business model and strategy might include:
- Demand generation.
- Free-download versions of the software.
- Subscription pricing for software (increasingly common) and support (always).
- Direct sales, and associated marketing.
Those look pretty similar to me.
Of course, there can still be differences between open and closed source. In particular: Read more
| Categories: Hadoop, Hortonworks, memcached, MongoDB, Open source | 8 Comments |
Hadoop distributions
Elephants! Elephants!
One elephant went out to play
Sat on a spider’s web one day.
They had such enormous fun
Called for another elephant to come.
Elephants! Elephants!
Two elephants went out to play
Sat on a spider’s web one day.
They had such enormous fun
Called for another elephant to come.
Elephants! Elephants!
Three elephants went out to play
Etc.
— Popular children’s song
It’s Strata week, with much Hadoop news, some of which I’ve been briefed on and some of which I haven’t. Rather than delve into fine competitive details, let’s step back and consider some generalities. First, about Hadoop distributions and distro providers:
- Conceptually, the starting point for a “Hadoop distribution” is some version of Apache Hadoop.
- Hortonworks is still focused on Hadoop 1 (without YARN and so on), because that’s what’s regarded as production-ready. But Hortonworks does like HCatalog.
- Cloudera straddles Hadoop 1 and Hadoop 2, shipping aspects of Hadoop 2 but not recommending them for production use.
- Some of the newer distros seem to be based on Hadoop 2, if the markitecture slides are to be believed.
- Optionally, the version numbers of different parts of Hadoop in a distribution could be a little mismatched, if the distro provider takes responsibility for testing them together.
- Cloudera seems more willing to do that than Hortonworks.
- Different distro providers may choose different sets of Apache Hadoop subprojects to include.
- Cloudera seems particularly expansive in what it is apt to include. Perhaps not coincidentally, Cloudera folks started various Hadoop subprojects.
- Optionally, distro providers’ additional proprietary code can be included, to be used either in addition to or instead of Apache Hadoop code. (In the latter case, marketing can then ensue about whether this is REALLY a Hadoop distribution.)
- Hortonworks markets from a “more open source than thou” stance, even though:
- It is not a purist in that regard.
- That marketing message is often communicated by Hortonworks’ very closed-source partners.
- Several distro providers, notably Cloudera, offer management suites as a big part of their proprietary value-add. Hortonworks, however, is focused on making open-source Ambari into a competitive management tool.
- Performance is another big area for proprietary code, especially from vendors who look at HDFS (Hadoop Distributed File System) and believe they can improve on it.
- I conjecture packaging/installation code is often proprietary, but that’s a minor issue that doesn’t get mentioned much.
- Hortonworks markets from a “more open source than thou” stance, even though:
- Optionally, third parties’ code can be provided, open or closed source as the case may be.
Most of the same observations could apply to Hadoop appliance vendors.
| Categories: Cloudera, Data warehouse appliances, EMC, Greenplum, Hadoop, Hortonworks, IBM and DB2, Intel, MapR, Market share and customer counts | 5 Comments |
Greenplum HAWQ
My former friends at Greenplum no longer talk to me, so in particular I wasn’t briefed on Pivotal HD and Greenplum HAWQ. Pivotal HD seems to be yet another Hadoop distribution, with the idea that you use Greenplum’s management tools. Greenplum HAWQ seems to be Greenplum tied to HDFS.
The basic idea seems to be much like what I mentioned a few days ago — the low-level file store for Greenplum can now be something else one has heard of before, namely HDFS (Hadoop Distributed File System, which is also an option for, say, NuoDB). Beyond that, two interesting quotes in a Greenplum blog post are:
When a query starts up, the data is loaded out of HDFS and into the HAWQ execution engine.
and
In addition, it has native support for HBase, supporting HBase predicate pushdown, hive[sic] connectivity, and offering a ton of intelligent features to retrieve HBase data.
The first sounds like the invisible loading that Daniel Abadi wrote about last September on Hadapt’s blog. (Edit: Actually, see Daniel’s comment below.) The second sounds like a good idea that, again, would also be a natural direction for vendors such as Hadapt.
| Categories: EMC, Greenplum, Hadapt, Hadoop, HBase, SQL/Hadoop integration | 14 Comments |
One database to rule them all?
Perhaps the single toughest question in all database technology is: Which different purposes can a single data store serve well? — or to phrase it more technically — Which different usage patterns can a single data store support efficiently? Ted Codd was on multiple sides of that issue, first suggesting that relational DBMS could do everything and then averring they could not. Mike Stonebraker too has been on multiple sides, first introducing universal DBMS attempts with Postgres and Illustra/Informix, then more recently suggesting the world needs 9 or so kinds of database technology. As for me — well, I agreed with Mike both times. 🙂
Since this is MUCH too big a subject for a single blog post, what I’ll do in this one is simply race through some background material. To a first approximation, this whole discussion is mainly about data layouts — but only if we interpret that concept broadly enough to comprise:
- Every level of storage (disk, RAM, etc.).
- Indexes, aggregates and raw data alike.
To date, nobody has ever discovered a data layout that is efficient for all usage patterns. As a general rule, simpler data layouts are often faster to write, while fancier ones can boost query performance. Specific tradeoffs include, but hardly are limited to: Read more