5 ms·

The problem for RethinkDB is that the firmware on Intel SSDs is advanced enough that it can speed up the normal, free MySQL engine (or postgresql, or oracle, ..

by Andys 17y ago

The problem for RethinkDB is that the firmware on Intel SSDs is advanced enough that it can speed up the normal, free MySQL engine (or postgresql, or oracle, ...) to almost the same sort of speeds. I am yet to see any evidence that RethinkDB's approach is anything but a niche for those who need to squeeze an extra 5-10% that advances in filesystems and flash firmware cannot.

igrigorik 17y ago
Huh, interesting. Any resources where I can learn more about these firmware optimizations? Intuitively, that doesn't make much sense: it would seem that dropping a lot of the software overhead associated with concurrency, etc, would yield a significant improvement. Having said that, it's also possible that the actual 'software overhead' is pretty much negligible when compared to disk access times. Would love to learn more on this.
- wmf 17y ago
  I'm not familiar with RethinkDB, but I have read the H-Store paper and I think some of its optimizations are applicable to RAM but not SSD. SSDs are much faster than disk, but I don't think they're fast enough that you can afford to eliminate caching or locking. In particular, good SSDs are internally parallel and require multiple concurrent I/Os for good performance, so you'll probably have to execute multiple transactions concurrently.
  - igrigorik 17y ago
    Well, if an average random access to disk is ~5ms, and an X25 Intel SSD is ~500 microseconds, then we're already talking a 10x difference and that's for a 'consumer grade' SSD. I'm sure the latency will come down over time as well. If you look at some of the PCI-E SSD solutions, then we're dipping below 100 microseconds, which means we're into 50-60x difference.
  - illumen 17y ago
    Indeed. Even with ram, concurrency is optimal on many server architectures. See NUMA, http://en.wikipedia.org/wiki/Non-Uniform_Memory_Access http://en.wikipedia.org/wiki/Non-Uniform_Memory_Access
coffeemug 17y ago
It's not that simple. The FTL addresses two fundamental problems with flash - slow random write performance and wear leveling. It works beautifully on consumer hardware, but performs rather poorly in an enterprise environment. For some workloads you can squeeze a lot more than 5-10% improvement out of the drives. But that's not the interesting part (most of today's workloads are read-intensive anyway). The interesting part comes from being able to execute existing operations in fundamentally different ways. When you're not restricted to sequential reads you can implement a huge chunk of database internals differently - different concurrency models, different implementations of certain joins, etc. This is where the bulk of the performance improvement comes from. Once you do this, you realize that a traditional bottleneck (I/O) is completely blown away. Suddenly, all kinds of things nobody ever bothered to optimize become performance bottlenecks (for example, the query plan is traditionally interpreted, not compiled to native code - not good enough once you get an I/O subsystem that's 250 times faster than what you used to have). Once you get rid of the software bottlenecks, you realize that you're limited by the bus. Since SSDs are highly parallelized devices, you have to change the way you interleave operations for optimal performance. That alone is another order of magnitude. In three years or so, the flash manufacturers will put chips on the SSDs that will allow you to send down programs to them (not unlike the shaders in video cards). That will likely be a bigger revolution than SSDs themselves. Where we are now is just the beginning. You're right that we haven't shown any evidence that our approach is anything but a niche. We will. This stuff just takes a long time to build.
- neilc 17y ago
  the query plan is traditionally interpreted, not compiled to native code Actually, System R (IBM's pioneering relation database from the mid 1970s) compiled query plans down to machine code.
- pedrocr 17y ago
  In three years or so, the flash manufacturers will put chips on the SSDs that will allow you to send down programs to them (not unlike the shaders in video cards). That will likely be a bigger revolution than SSDs themselves. Where we are now is just the beginning. This sounds crazy. SSDs have all this firmware and processing power to make them behave like hard drives. If we want to drive the underlying storage directly we might as well rip all that out and let the OS drive the flash directly from the main CPU. Why would we want to be sending programs into the black box? What can the firmware do that the main CPU couldn't if we stopped attaching flash as SATA and instead just created a direct connection that can DMA back and forth to main memory? Some Linux developers have made that point, that they would rather be implementing their own filesystems directly on the flash than dealing with a firmware that is trying to make it appear that the SSD is a hard drive but that then needs TRIM to work around the fact that that is not true. These firmwares are nice for Intel by letting them turn a commodity (flash) into a differentiated (and higher margin) product based on the code in the firmware. Considering Linux already has filesystems that can operate directly over flash and that better ones can be written I'd say we would be better off just getting direct access to the flash.
Devilboy 17y ago
We committed to SQL Server a long time ago. It's served us very well and it will take a lot of effort to replace it. To keep up with increasing workloads we've had to purchase reasonably expensive hardware - I think the last server cost us almost $100k. The #1 bottleneck has always been disk IO. To compensate for slow disks you need to increase RAM and make big RAID arrays, both fairly expensive options compared to the Intel SSDs available now. Upgrading our current hardware with only $10k worth of SSDs will add at least a year or two to the life of our SQL Servers.

by Andys 17y ago

igrigorik 17y ago

Huh, interesting. Any resources where I can learn more about these firmware optimizations? Intuitively, that doesn't make much sense: it would seem that dropping a lot of the software overhead associated with concurrency, etc, would yield a significant improvement. Having said that, it's also possible that the actual 'software overhead' is pretty much negligible when compared to disk access times. Would love to learn more on this.

wmf 17y ago
I'm not familiar with RethinkDB, but I have read the H-Store paper and I think some of its optimizations are applicable to RAM but not SSD. SSDs are much faster than disk, but I don't think they're fast enough that you can afford to eliminate caching or locking. In particular, good SSDs are internally parallel and require multiple concurrent I/Os for good performance, so you'll probably have to execute multiple transactions concurrently.
- igrigorik 17y ago
  Well, if an average random access to disk is ~5ms, and an X25 Intel SSD is ~500 microseconds, then we're already talking a 10x difference and that's for a 'consumer grade' SSD. I'm sure the latency will come down over time as well. If you look at some of the PCI-E SSD solutions, then we're dipping below 100 microseconds, which means we're into 50-60x difference.
- illumen 17y ago
  Indeed. Even with ram, concurrency is optimal on many server architectures. See NUMA, http://en.wikipedia.org/wiki/Non-Uniform_Memory_Access http://en.wikipedia.org/wiki/Non-Uniform_Memory_Access

coffeemug 17y ago

It's not that simple. The FTL addresses two fundamental problems with flash - slow random write performance and wear leveling. It works beautifully on consumer hardware, but performs rather poorly in an enterprise environment. For some workloads you can squeeze a lot more than 5-10% improvement out of the drives. But that's not the interesting part (most of today's workloads are read-intensive anyway). The interesting part comes from being able to execute existing operations in fundamentally different ways. When you're not restricted to sequential reads you can implement a huge chunk of database internals differently - different concurrency models, different implementations of certain joins, etc. This is where the bulk of the performance improvement comes from. Once you do this, you realize that a traditional bottleneck (I/O) is completely blown away. Suddenly, all kinds of things nobody ever bothered to optimize become performance bottlenecks (for example, the query plan is traditionally interpreted, not compiled to native code - not good enough once you get an I/O subsystem that's 250 times faster than what you used to have). Once you get rid of the software bottlenecks, you realize that you're limited by the bus. Since SSDs are highly parallelized devices, you have to change the way you interleave operations for optimal performance. That alone is another order of magnitude. In three years or so, the flash manufacturers will put chips on the SSDs that will allow you to send down programs to them (not unlike the shaders in video cards). That will likely be a bigger revolution than SSDs themselves. Where we are now is just the beginning. You're right that we haven't shown any evidence that our approach is anything but a niche. We will. This stuff just takes a long time to build.

neilc 17y ago
the query plan is traditionally interpreted, not compiled to native code Actually, System R (IBM's pioneering relation database from the mid 1970s) compiled query plans down to machine code.
pedrocr 17y ago
In three years or so, the flash manufacturers will put chips on the SSDs that will allow you to send down programs to them (not unlike the shaders in video cards). That will likely be a bigger revolution than SSDs themselves. Where we are now is just the beginning. This sounds crazy. SSDs have all this firmware and processing power to make them behave like hard drives. If we want to drive the underlying storage directly we might as well rip all that out and let the OS drive the flash directly from the main CPU. Why would we want to be sending programs into the black box? What can the firmware do that the main CPU couldn't if we stopped attaching flash as SATA and instead just created a direct connection that can DMA back and forth to main memory? Some Linux developers have made that point, that they would rather be implementing their own filesystems directly on the flash than dealing with a firmware that is trying to make it appear that the SSD is a hard drive but that then needs TRIM to work around the fact that that is not true. These firmwares are nice for Intel by letting them turn a commodity (flash) into a differentiated (and higher margin) product based on the code in the firmware. Considering Linux already has filesystems that can operate directly over flash and that better ones can be written I'd say we would be better off just getting direct access to the flash.

Devilboy 17y ago

We committed to SQL Server a long time ago. It's served us very well and it will take a lot of effort to replace it. To keep up with increasing workloads we've had to purchase reasonably expensive hardware - I think the last server cost us almost $100k. The #1 bottleneck has always been disk IO. To compensate for slow disks you need to increase RAM and make big RAID arrays, both fairly expensive options compared to the Intel SSDs available now. Upgrading our current hardware with only $10k worth of SSDs will add at least a year or two to the life of our SQL Servers.