Four Myths of In-Memory Computing

As any fast growing technology In-Memory Computing has attracted a lot of interest and writing in the last couple of years. It’s bound to happen that some of the information gets stale pretty quickly – while other is simply not very accurate to being with. And thus myths are starting to grow and take hold.

I want to talk about some of the misconceptions that we are hearing almost on a daily basis here at GridGain and provide necessary clarification (at least from our our point of view). Being one of the oldest company working in in-memory computing space for the last 7 years we’ve heard and seen all of it by now – and earned a certain amount of perspective on what in-memory computing is and, most importantly, what it isn’t.

In-Memory Computing

Let’s start at… the beginning. What is the in-memory computing? Kirill Sheynkman from RTP Ventures gave the following crisp definition which I like very much:

“In-Memory Computing is based on a memory-first principle utilizing high-performance, integrated, distributed main memory systems to compute and transact on large-scale data sets in real-time – orders of magnitude faster than traditional disk-based systems.”

The most important part of this definition is “memory-first principle”. Let me explain…

Memory-First Principle

Memory-first principle (or architecture) refers to a fundamental set of algorithmic optimizations one can take advantage of when data is stored mainly in Random Access Memory (RAM) vs. in block-level devices like HDD or SSD.

RAM has dramatically different characteristics than block-level devices including disks, SSDs or Flash-on-PCI-E arrays. Not only RAM is ~1000x times faster as a physical medium, it completely eliminates the traditional overhead of block-level devices including marshaling, paging, buffering, memory-mapping, possible networking, OS I/O, and I/O controller.

Let’s look at example: say you need to read a single record in your program.

In in-memory context your code will be compiled to interact with memory controller and read it directly from local RAM in the exact format you need (i.e. your object representation in particular programming language) – in most cases that will result in a simple pointer arithmetic. If you use proper vectorized execution technique – you’ll often read it from L2 cache of your CPUs. All in all – we are talking about nanoseconds and this performance is guaranteed for all cases.

If you read the same record form block-level device – you are in for a very different ride… Your code will have to deal with OS I/O, buffered read, I/O controller, seek time of the device, and de-marshaling back the byte stream that you get from it to an object representation that you actually need. In worst case scenario – we’re talking dozen milliseconds. Note that SSDs and Flash-on-PCI-E only improves portion of the overhead related to seek time of the device (and only marginally).

Taking advantage of these differences and optimizing your software accordingly – is what memory-first principle is all about.

Now, let’s get to the myths.

Myth #1: It’s Too Expensive

This is one of the most enduring myths of in-memory computing. Today – it’s simply not true. Five or ten years ago, however, it was indeed true. Look at the historical chart of USD/MB storage pricing to see why:

The interesting trend is that price of RAM is dropping 30% every 12 months or so and is solidly on the same trajectory as price of HDD which is for all practical reasons is almost zero (enterprises care more today about heat, energy, space than a raw price of the device).

The price of 1TB RAM cluster today is anywhere between $20K and $40K – and that includes all the CPUs, over petabyte of disk based storage, networking, etc. CIsco UCS, for example, offers very competitive white-label blades in $30K range for 1TB RAM setup: Smart shoppers on eBay can easily beat even the $20K price barrier (as we did at GridGain for our own recent testing/CI cluster).

In a few years from now the same 1TB TAM cluster setup will be available for $10K-15K – which makes it all but commodity at that level.

And don’t forget about Memory Channel Storage (MCS) that aims to revolutionize storage by providing the Flash-in-DIMM form factor – I’ve blogged about it few weeks ago.

Myth #2: It’s Not Durable

This myths is based on a deep rooted misunderstanding about in-memory computing. Blame us as well as other in-memory computing vendors as we evidently did a pretty poor job on this subject.

The fact of the matter is – almost all in-memory computing middleware (apart from very simplistic ones) offer one or multiple strategies for in-memory backups, durable storage backups, disk-based swap space overflow, etc.

More sophisticated vendors provide a comprehensive tiered storage approach where users can decide what portion of the overall data set is stored in RAM, local disk swap space or RDBMS/HDFS – where each tier can store progressively more data but with progressively longer latencies.

Yet another source of confusion is the difference between operational datasets and historical datasets. In-memory computing is not aimed at replacing enterprise data warehouse (EDW), backup or offline storage services – like Hadoop, for example. In-memory computing is aiming at improving operational datasets that require mixed OLTP and OLAP processing and in most cases are less than 10TB in size. In other words – in-memory computing doesn’t suffer from all-or-nothing syndrome and never requires you to keep all data in memory.

If you consider the totally of the data stored by any one enterprise – the disk still has a clear place as a medium for offline, backup or traditional EDW use cases – and thus the durability is there where it always has been.

Myth #3: Flash Is Fast Enough

The variations of this myth include the following:

  • Our business doesn’t need this super-fast processing (likely shortsighted)
  • We can mount RAM disk and effectively get in-memory processing (wrong)
  • We can replace HDDs with SSDs to get the performance (depends)

Mounting RAM disk is a very poor way of utilizing memory from every technical angle (see above).

As far as SSDs – for some uses cases – the marginal performance gain that you can extract from flash storage over spinning disk could be enough. In fact – if you are absolutely certain that the marginal improvements is all you ever need for a particular application – the flash storage is the best bet today.

However, for a rapidly growing number of use cases – speed matters. And it matters more and for more businesses every day. In-memory computing is not about marginal 2-3x improvement – it is about giving you 10-100x improvements enabling new businesses and services that simply weren’t feasible before.

There’s one story that I’ve been telling for quite some time now and it shows a very telling example of how in-memory computing relates to speed…

Around 6 years ago GridGain had a financial customer who had a small application (~1500 LOC in Java) that took 30 seconds to prepare a chart and a table with some historical statistical results for a given basket of stocks (all stored in Oracle RDBMS). They wanted to put it online on their website. Naturally, users won’t wait for half a minute after they pressed the button – so, the task was to make it around 5-6 seconds. Now – how do you make something 5 times faster?

We initially looked at every possible angle: faster disks (even SSD which were very expensive then), RAID systems, faster CPU, rewriting everything in C/C++, running on different OS, Oracle RAC – or any combination of thereof. But nothing would make an application run 5x faster – not even close… Only when we brought the the dataset in memory and parallelized the processing over 5 machines using in-memory MapReduce – we were able to get results in less than 4 seconds!

The morale of the story is that you don’t have to have NASA-size problem to utilize in-memory computing. In fact, every day thousands of businesses solving performance problem that look initially trivial but in the end could only be solved with in-memory computing speed.

Speed also matters in the raw sense as well. Look at this diagram from Stanford about relative performance of disks, flash and RAM:

As DRAM closes its pricing gap with flash such dramatic difference in raw performance will become more and more pronounced and tangible for business of all sizes.

Myth #4: It’s About In-Memory Databases

This is one of those mis-conceptions that you hear mostly from analysts. Most analysts look at SAP HANA, Oracle Exalytics or something like QlikView – and they conclude that this is all that in-memory computing is all about, i.e. database or in-memory caching for faster analytics.

There’s a logic behind it, of course, but I think this is rather a bit shortsighted view.

First of all, in-memory computing is not a product – it is a technology. The technology is used to built products. In fact – nobody sells just “in-memory computing” but rather products that are built with in-memory computing.

I also think that in-memory databases are important use case… for today. They solve a specific use case that everyone readily understands, i.e. faster system of records. It’s sort of a low hanging fruit of in-memory computing and it gets in-memory computing popularized.

I do, however, think that the long term growth for in-memory computing will come from streaming use cases. Let me explain.

Streaming processing is typically characterized by a massive rate at which events are coming into a system. Number of potential customers we’ve talked to indicated to us that they need to process a sustained stream of up to 100,000 events per second with out a single event loss. For a typical 30 seconds sliding processing window we are dealing with 3,000,000 events shifting by 100,000 every second which have to be individually indexed, continuously processed in real-time and eventually stored.

This downpour will choke any disk I/O (spinning or flash). The only feasible way to sustain this load and corresponding business processing is to use in-memory computing technology. There’s simply no other storage technology today that support that level of requirements.

So we strongly believe that in-memory computing will reign supreme in streaming processing.

GridGain In-Memory Database: Plain English Overview

I picked this chapter up from the GridGain’s Document Center. I like it as it gives simple, plain English high-level overview of our In-Memory Database: no coding, no diagrams, no deep dives. Just quick and easy rundown of what’s there…

At a Glance

GridGain IMDB is a distributed, Java-based, object-based key-value datastore. Logically it can be viewed as a collection of one or more caches (a.k.a maps or dictionaries). Each cache is a distributed collection of key-value pairs. Both key and value are represented as Java object and can be of any user-defined type.

Every cache must be pre-configured individually and cannot be created on the fly (due to distributed consistency semantics). You’ll find that cache and cache projections will be your main API entry points while working with GridGain IMDB in embedded mode.

Each cache has many configuration properties with the main one being its type. GridGain IMDB supports three cache types: local, replicated and partitioned.

As name implies the local mode stores all data locally without any distribution providing lightweight transactional local storage. Replicated cache replicates (copies) data to all nodes in the cluster resulting in best high availability but reducing overall database in-memory capacity since data is copied everywhere. Partitioned mode is the most scalable mode as it equally partitions data across all nodes in the cluster so that each node is only responsible for a small portion of the data.

Combination of these storage modes in a single database (as well as many specific configuration and optimization properties available for each mode) make GridGain IMDB very convenient distributed datastore as it doesn’t force you to use just one specific storage model.

GridGain IMDB stores data in layered storage system that consists of 4 layers: JVM on-heap memory, JVM off-heap memory, local disk-based swap space, and optional durable cache store. Each layer can store more data but entails progressively higher latencies for data access. Developer has full control over configuration of these layers.

Another interesting characteristic of GridGain IMDB is that it was developed first as a highly distributed system and only later it became a full fledged database. This reversed approach makes data and processing distribution a natural capability of the database.

GridGain IMDB is based on unique HyperClustering technology that enables GridGain IMDB scale to 1000s of nodes in a single transactional topology (based on actual production customers).

GridGain IMDB clustering is based on peer-to-peer topology, its transaction implementation is based on advanced MVCC-based design, and its partitioning is based on automatic multilayer consistent hashing implementation – free from sharding limitations or other crude data distribution approaches.

High Performance Computing (HPC) Integration

One of the most unique characteristics of GridGain IMDB is the full integration of In-Memory HPC at the core of the database.

Many traditional RDBMS and No/NewSQL databases only address data storage and rudimentary data processing. In this scenario the data is retrieved from the database and has to be moved to some other processing node. Once data is processed, it is usually discarded.

Such data movement between different layers, even minimal, is almost always at the core of the scalability and performance problems in highly distributed systems.

GridGain IMDB was designed from the ground up to minimize unnecessary data movements and instead move computations to the data whenever possible – hence its integration of HPC technology is at the very core of the database. Computations are dramatically smaller in size – often by factor of 1000x, they don’t change as often as the data, have strong and easily defined affinity to the data they require, and typically provide only negligible load on network and JVMs.

What is even more important – this approach allows for clean processing parallelization of data stored in the database since the computing task can now be intelligently split into sub-tasks that can be sent to remote nodes to work in parallel on their respective local data sub-sets with absolutely zero global resource contention.

GridGain IMDB supports MapReduce, distributed SQL, MPP, MPI, RPC, File System, and Document API type of data processing and querying – the deepest and the widest eco-system of HPC processing paradigms provided by any database or HPC framework.

Accessing Database

GridGain IMDB can be queried and programmed in many different ways. In external context you can use Java, C++, or C# drivers. GridGain IMDB also natively supports custom REST and Memcached protocol.

In embedded mode you can use distributed SQL and JDBC as well as Lucene, Text and full-scan queries. For complex data computations you can use in-memory MapReduce, MPP, RPC and MPI-based processing. All programming techniques in embedded mode have deeply customizable APIs including distributed extensions to SQL, Java or Scala-based custom SQL functions, streaming MapReduce, distributed continuations, connected tasks support, etc.

GridGain IMDB also provides in-memory file system (GGFS – GridGain File System) as well as full support for MongoDB Document API protocol.

Embedded vs. External Access

Unlike many traditional, NewSQL and NoSQL databases GridGain IMDB is designed to be easily programmable in embedded mode.

Traditional (external) approach dictates that database should be deployed separately and the data processing applications access it through some networking protocol and client library (i.e. the driver). This implies significant driver overhead and data movement that makes any HPC or real-time database processing impossible as we discussed above.

While supporting the external access as well via its C++, .NET, and Java drivers – GridGain IMDB also natively supports embedded mode where data processing logic can be deployed directly into the database itself and therefore can be programmatically accessed in the same process. In other words, GridGain IMDB allows to initiate a distributed data processing task right from the database process itself removing any driver overhead and its significant API limitations – enabling rich functionality and sub-millisecond response for complex distributed data processing tasks.

Among many benefits, this is becoming critically important capability for rapidly growing machine-to-machine and streaming use cases that don’t have human interaction delays built in and require minimal latencies and linear horizontal scalability.

Fault Tolerance and Durability

GridGain IMDB provides advanced capabilities when it comes to fault tolerance and durability.

Each cache can be configured with one or more active backups which provides data redundancy when a node crashes as well as improved performance in read-mostly scenarios. On topology changes (node leaves or joins) the comprehensive pre-loading subsystem will make sure that data is synchronously or asynchronously re-partitioned while maintaining the desired consistency and availability. Each cache can be independently configured for transactional read-through and write-through to a durable storage such as RDBMS, HDFS, or file system to make sure that data is backed up in durable datastore, if required.

In case of network segmentation, a.k.a. “split-brain” problem, GridGain IMDB provides pluggable segmentation resolution architecture where dirty writes or reads are impossible regardless of how segmented your cluster gets.

For complex and mission critical deployments GridGain IMDB provides data center replication. When data center replication is turned on, GridGain IMDB will automatically make sure that each data center is consistently backing up its data to other data centers (there can be more than one). GridGain supports both active-active and active-passive modes for replication.


GridGain IMDB has full support for distributed transactions supporting all ACID properties including support for Optimistic and Pessimistic concurrency levels and READ_COMMITTED, REPEATABLE_READ, and SERIALIZABLE isolation levels.

For JEE environments, like application servers, GridGain IMDB provides automatic integration with JTA/XA. Essentially GridGain becomes an XA resource and will automatically check if there is an active JTA transaction present.

In addition to transactions where GridGain IMDB allows to execute multiple data operations atomically, GridGain also supports single atomic CAS (compare-and-set) operations, such as put-if-absent, compare-and-set, and compare-and-remove.

For more information head over to GridGain’s In-Memory Database.