Solid-state memory
Discussion of how developments in solid-state memory will affect database management. Related subjects include:
- Data warehouse appliances
- (in The Monash Report) The future of diskless PCs
Generally available Kudu
I talked with Cloudera about Kudu in early May. Besides giving me a lot of information about Kudu, Cloudera also helped confirm some trends I’m seeing elsewhere, including:
- Security is an ever bigger deal.
- There’s a lot of interest in data warehouses (perhaps really data marts) that are updated in human real-time.
- Prospects for that respond well to the actual term “data warehouse”, at least when preceded by some modifier to suggest that it’s modern/low-latency/non-batch or whatever.
- Flash is often — but not yet always — preferred over disk for that kind of use.
- Sometimes these data stores are greenfield. When they’re migrations, they come more commonly from analytic RDBMS or data warehouse appliance (the most commonly mentioned ones are Teradata, Netezza and Vertica, but that’s perhaps just due to those product lines’ market share), rather than from general purpose DBMS such as Oracle or SQL Server.
- Intel is making it ever easier to vectorize CPU operations, and analytic data managers are increasingly taking advantage of this possibility.
Now let’s talk about Kudu itself. As I discussed at length in September 2015, Kudu is:
- A data storage system introduced by Cloudera (and subsequently open-sourced).
- Columnar.
- Updatable in human real-time.
- Meant to serve as the data storage tier for Impala and Spark.
Kudu’s adoption and roll-out story starts: Read more
Interana
Interana has an interesting story, in technology and business model alike. For starters:
- Interana does ad-hoc event series analytics, which they call “interactive behavioral analytics solutions”.
- Interana has a full-stack analytic offering, include:
- Its own columnar DBMS …
- … which has a non-SQL DML (Data Manipulation Language) meant to handle event series a lot more fluently than SQL does, but which the user is never expected to learn because …
- … there also are BI-like visual analytics tools that support plenty of drilldown.
- Interana sells all this to “product” departments rather than marketing, because marketing doesn’t sufficiently value Interana’s ad-hoc query flexibility.
- Interana boasts >40 customers, with annual subscription fees ranging from high 5 figures to low 7 digits.
And to be clear — if we leave aside any questions of marketing-name sizzle, this really is business intelligence. The closest Interana comes to helping with predictive modeling is giving its ad-hoc users inspiration as to where they should focus their modeling attention.
Interana also has an interesting twist in its business model, which I hope can be used successfully by other enterprise software startups as well. Read more
Notes on the transition to the cloud
1. The cloud is super-hot. Duh. And so, like any hot buzzword, “cloud” means different things to different marketers. Four of the biggest things that have been called “cloud” are:
- The Amazon cloud, Microsoft Azure, and their competitors, aka public cloud.
- Software as a service, aka SaaS.
- Co-location in off-premises data centers, aka colo.
- On-premises clusters (truly on-prem or colo as the case may be) designed to run a broad variety of applications, aka private cloud.
Further, there’s always the idea of hybrid cloud, in which a vendor peddles private cloud systems (usually appliances) running similar technology stacks to what they run in their proprietary public clouds. A number of vendors have backed away from such stories, but a few are still pushing it, including Oracle and Microsoft.
This is a good example of Monash’s Laws of Commercial Semantics.
2. Due to economies of scale, only a few companies should operate their own data centers, aka true on-prem(ises). The rest should use some combination of colo, SaaS, and public cloud.
This fact now seems to be widely understood.
Cloudera Kudu deep dive
This is part of a three-post series on Kudu, a new data storage system from Cloudera.
- Part 1 is an overview of Kudu technology.
- Part 2 (this post) is a lengthy dive into how Kudu writes and reads data.
- Part 3 is a brief speculation as to Kudu’s eventual market significance.
Let’s talk in more detail about how Kudu stores data.
- As previously noted, inserts land in an in-memory row store, which is periodically flushed to the column store on disk. Queries are federated between these two stores. Vertica taught us to call these the WOS (Write-Optimized Store) and ROS (Read-Optimized Store) respectively, and I’ll use that terminology here.
- Part of the ROS is actually another in-memory store, aka the DeltaMemStore, where updates and deletes land before being applied to the DiskRowSets. These stores are managed separately for each DiskRowSet. DeltaMemStores are checked at query time to confirm whether what’s in the persistent store is actually up to date.
- A major design goal for Kudu is that compaction should never block — nor greatly slow — other work. In support of that:
- Compaction is done, server-by-server, via a low-priority but otherwise always-on background process.
- There is a configurable maximum to how big a compaction process can be — more precisely, the limit is to how much data the process can work on at once. The current default figure = 128 MB, which is 4X the size of a DiskRowSet.
- When done, Kudu runs a little optimization to figure out which 128 MB to compact next.
- Every tablet has its own write-ahead log.
- This creates a practical limitation on the number of tablets …
- … because each tablet is causing its own stream of writes to “disk” …
- … but it’s only a limitation if your “disk” really is all spinning disk …
- … because multiple simultaneous streams work great with solid-state memory.
- Log retention is configurable, typically the greater of 5 minutes or 128 MB.
- Metadata is cached in RAM. Therefore:
- ALTER TABLE kinds of operations that can be done by metadata changes only — i.e. adding/dropping/renaming columns — can be instantaneous.
- To keep from being screwed up by this, the WOS maintains a column that labels rows by which schema version they were created under. I immediately called this MSCC — Multi-Schema Concurrency Control 🙂 — and Todd Lipcon agreed.
- Durability, as usual, boils down to “Wait until a quorum has done the writes”, with a configurable option as to what constitutes a “write”.
- Servers write to their respective write-ahead logs, then acknowledge having done so.
- If it isn’t too much of a potential bottleneck — e.g. if persistence is on flash — the acknowledgements may wait until the log has been fsynced to persistent storage.
- There’s a “thick” client library which, among other things, knows enough about the partitioning scheme to go straight to the correct node(s) on a cluster.
| Categories: Cloudera, Columnar database management, Hadoop, Solid-state memory, SQL/Hadoop integration | 25 Comments |
Introduction to Cloudera Kudu
This is part of a three-post series on Kudu, a new data storage system from Cloudera.
- Part 1 (this post) is an overview of Kudu technology.
- Part 2 is a lengthy dive into how Kudu writes and reads data.
- Part 3 is a brief speculation as to Kudu’s eventual market significance.
Cloudera is introducing a new open source project, Kudu,* which from Cloudera’s standpoint is meant to eventually become the single best underpinning for analytics on the Hadoop stack. I’ve spent multiple hours discussing Kudu with Cloudera, mainly with Todd Lipcon. Any errors are of course entirely mine.
*Like the impala, the kudu is a kind of antelope. I knew that, because I enjoy word games. What I didn’t know — and which is germane to the naming choice — is that the kudu has stripes. 🙂
For starters:
- Kudu is an alternative to HDFS (Hadoop Distributed File System), or to HBase.
- Kudu is meant to be the underpinning for Impala, Spark and other analytic frameworks or engines.
- Kudu is not meant for OLTP (OnLine Transaction Processing), at least in any foreseeable release. For example:
- Kudu doesn’t support multi-row transactions.
- There are no active efforts to front-end Kudu with an engine that is fast at single-row queries.
- Kudu is rather columnar, except for transitory in-memory stores.
- Kudu’s core design points are that it should:
- Accept data very quickly.
- Immediately make that data available for analytics.
- More specifically, Kudu is meant to accept, along with slower forms of input:
- Lots of fast random writes, e.g. of web interactions.
- Streams, viewed as a succession of inserts.
- Updates and inserts alike.
- The core “real-time” use cases for which Kudu is designed are, unsurprisingly:
- Low-latency business intelligence.
- Predictive model scoring.
- Kudu is designed to work fine with spinning disk, and indeed has been tested to date mainly on disk-only nodes. Even so, Kudu’s architecture is optimized for the assumption that there will be at least some flash on the node.
- Kudu is designed primarily to support relational/SQL processing. However, Kudu also has a nested-data roadmap, which of course starts with supporting the analogous capabilities in Impala.
Where the innovation is
I hoped to write a reasonable overview of current- to medium-term future IT innovation. Yeah, right. 🙂 But if we abandon any hope that this post could be comprehensive, I can at least say:
1. Back in 2011, I ranted against the term Big Data, but expressed more fondness for the V words — Volume, Velocity, Variety and Variability. That said, when it comes to data management and movement, solutions to the V problems have generally been sketched out.
- Volume has been solved. There are Hadoop installations with 100s of petabytes of data, analytic RDBMS with 10s of petabytes, general-purpose Exadata sites with petabytes, and 10s/100s of petabytes of analytic Accumulo at the NSA. Further examples abound.
- Velocity is being solved. My recent post on Hadoop-based streaming suggests how. In other use cases, velocity is addressed via memory-centric RDBMS.
- Variety and Variability have been solved. MongoDB, Cassandra and perhaps others are strong NoSQL choices. Schema-on-need is in earlier days, but may help too.
2. Even so, there’s much room for innovation around data movement and management. I’d start with:
- Product maturity is a huge issue for all the above, and will remain one for years.
- Hadoop and Spark show that application execution engines:
- Have a lot of innovation ahead of them.
- Are tightly entwined with data management, and with data movement as well.
- Hadoop is due for another refactoring, focused on both in-memory and persistent storage.
- There are many issues in storage that can affect data technologies as well, including but not limited to:
- Solid-state (flash or post-flash) vs. spinning disk.
- Networked vs. direct-attached.
- Virtualized vs. identifiable-physical.
- Object/file/block.
- Graph analytics and data management are still confused.
3. As I suggested last year, data transformation is an important area for innovation. Read more
Notes from a visit to Teradata
I spent a day with Teradata in Rancho Bernardo last week. Most of what we discussed is confidential, but I think the non-confidential parts and my general impressions add up to enough for a post.
First, let’s catch up with some personnel gossip. So far as I can tell:
- Scott Gnau runs most of Teradata’s development, product management, and product marketing, the big exception being that …
- … Darryl McDonald run the apps part (Aprimo and so on), and no longer is head of marketing.
- Oliver Ratzesberger runs Teradata’s software development.
- Jeff Carter has returned to his roots and runs the hardware part, in place of Carson Schmidt.
- Aster founders Mayank Bawa and Tasso Argyros have left Teradata (perhaps some earn-out period ended).
- Carson is temporarily running Aster development (in place of Mayank), and has some sort of evangelism role waiting after that.
- With the acquisition of Hadapt, Teradata gets some attention from Dan Abadi. Also, they’re retaining Justin Borgman.
The biggest change in my general impressions about Teradata is that they’re having smart thoughts about the cloud. At least, Oliver is. All details are confidential, and I wouldn’t necessarily expect them to become clear even in October (which once again is the month for Teradata’s user conference). My main concern about all that is whether Teradata’s engineering team can successfully execute on Oliver’s directives. I’m optimistic, but I don’t have a lot of detail to support my good feelings.
In some quick-and-dirty positioning and sales qualification notes, which crystallize what we already knew before:
- The Teradata 1xxx series is focused on cost-per-bit.
- The Teradata 2xxx series is focused on cost-per-query. It is commonly Teradata’s “lead” product, at least for new customers.
- The Teradata 6xxx series is supposed to be able to do “everything”.
- The Teradata Aster “Discovery Analytics” platform is sold mainly to customers who have a specific high-value problem to solve. (Randy Lea gave me a nice round dollar number, but I won’t share it.) I like that approach, as it obviates much of the concern about “Wait — is this strategic for us long-term, given that we also have both Teradata database and Hadoop clusters?”
Also: Read more
| Categories: Aster Data, Data warehouse appliances, Data warehousing, Hadapt, Hadoop, MapReduce, Solid-state memory, Teradata | 2 Comments |
Notes and comments, May 6, 2014
After visiting California recently, I made a flurry of posts, several of which generated considerable discussion.
- My claim that Spark will replace Hadoop MapReduce got much Twitter attention — including some high-profile endorsements — and also some responses here.
- My MemSQL post led to a vigorous comparison of MemSQL vs. VoltDB.
- My post on hardware and storage spawned a lively discussion of Hadoop hardware pricing; even Cloudera wound up disagreeing with what I reported Cloudera as having said. 🙂 Sadly, there was less response to the part about the partial (!) end of Moore’s Law.
- My Cloudera/SQL/Impala/Hive apparently was well-balanced, in that it got attacked from multiple sides via Twitter & email. Apparently, I was too hard on Impala, I was too hard on Hive, and I was too hard on boxes full of cardboard file cards as well.
- My post on the Intel/Cloudera deal garnered a comment reminding us Dell had pushed the Intel distro.
- My CitusDB post picked up a few clarifying comments.
Here is a catch-all post to complete the set. Read more
Hardware and storage notes
My California trip last week focused mainly on software — duh! — but I had some interesting hardware/storage/architecture discussions as well, especially in the areas of:
- Rack- or data-center-scale systems.
- The real or imagined demise of Moore’s Law.
- Flash.
I also got updated as to typical Hadoop hardware.
If systems are designed at the whole-rack level or higher, then there can be much more flexibility and efficiency in terms of mixing and connecting CPU, RAM and storage. The Google/Facebook/Amazon cool kids are widely understood to be following this approach, so others are naturally considering it as well. My most interesting of several mentions of that point was when I got the chance to talk with Berkeley computer architecture guru Dave Patterson, who’s working on plans for 100-petabyte/terabit-networking kinds of systems, for usage after 2020 or so. (If you’re interested, you might want to contact him; I’m sure he’d love more commercial sponsorship.)
One of Dave’s design assumptions is that Moore’s Law really will end soon (or at least greatly slow down), if by Moore’s Law you mean that every 18 months or so one can get twice as many transistors onto a chip of the same area and cost than one could before. However, while he thinks that applies to CPU and RAM, Dave thinks flash is an exception. I gathered that he thinks the power/heat reasons for Moore’s Law to end will be much harder to defeat than the other ones; note that flash, because of what it’s used for, has vastly less power running through it than CPU or RAM do.
| Categories: Amazon and its cloud, Buying processes, Cloudera, Facebook, Google, Intel, Memory-centric data management, Pricing, Solid-state memory | 19 Comments |
MemSQL 3.0
Memory-centric data management is confusing. And so I’m going to clarify a couple of things about MemSQL 3.0 even though I don’t yet have a lot of details.* They are:
- MemSQL has historically been an in-memory row store, which as of last year scales out.
- It turns out that the MemSQL row store actually has two table types. One is scaled out. The other — called “reference” — is replicated on every node.
- MemSQL has now added a third table type, which is columnar and which resides in flash memory.
- If you want to keep data in, for example, both the scale-out row store and the column store, you’d have to copy/replicate it within MemSQL. And if you wanted to access data from both versions at once (e.g. because different copies cover different time periods), you’d likely have to do a UNION or something like that.
*MemSQL’s first columnar offering sounds pretty basic; for example, there’s no columnar compression yet. (Edit: Oops, that’s not accurate. See comment below.) But at least they actually have one, which puts them ahead of many other row-based RDBMS vendors that come to mind.
And to hammer home the contrast:
- IBM, Oracle and Microsoft, which all sell row-based DBMS meant to run on disk or other persistent storage, have added or will add columnar options that run in RAM.
- MemSQL, which sells a row-based DBMS that runs in RAM, has added a columnar option that runs in persistent solid-state storage.