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With the current prices and the lack of availability, the best 2022 server hardware for me will be 2018 server hardware. The one thing that's relatively new-is

With the current prices and the lack of availability, the best 2022 server hardware for me will be 2018 server hardware. The one thing that's relatively new-ish that I'd like to play with is persistent memory. But I'm curious about it for embedded applications where power is not assured. For servers? I don't understand the use case, because datacenters are where we have the most consistent power. Perhaps it'd be more interesting if I ran workloads on large datasets...

sidibe 5y ago
Persistent memory has some other advantages that make it good for datacenters. Mainly it is faster than SSD and cheaper than DRAM.
dragontamer 5y ago
I don't think Intel really knew what they were going for with Optane / persistent memory. They had an invention, it had a bunch of interesting stats, and they were hoping someone out there would figure out a use. Databases seem like the obvious answer. Persistent memory / Optane is much faster than NAND Flash... but less dense than NAND Flash. Its also slower than DRAM, but more dense, so it sits in between. Whether or not that's useful remains to be seen.
- haimez 5y ago
  You might use such a thing in database systems for, eg: 1. The write ahead log, for faster I/O than a direct flush to SSD 2. Staging disk cache entries to persistent memory before a planned host/process restart for faster subsequent DRAM cache warming The problem with 1 is that you still need to periodically flush to disk (at least once persistent storage is full) which means it’s only an improvement in burst activity and not peak throughput. The problem with both is complexity of implementation to deliver functionality that can only be used on a (currently) relatively uncommon subset of servers. Probably not something that Postgres would rush to implement, but potentially something that MSSQL or Oracle might consider as a premium feature. Disclaimer: I haven’t looked into the details of optane and how you interface with that storage in software.
benlivengood 5y ago
Transactional workloads (databases, pubsubs, workflow coordinators) benefit the most from persistent memory because write latency to storage dominates performance (a transaction must be committed to permanent storage before the client can be informed of success, and if there is contention between transactions they must wait and proceed serially). Persistent memory is about 100 times faster (300ns vs. 30us latency) than NAND and is writeable in-place at byte granularity vs. multi-KB erasable blocks.
- jeffbee 5y ago
  > transaction must be committed to permanent storage before the client can be informed of success Transactions must be durable, but that doesn't mean they can't be committed to RAM initially. There are large-scale database systems you have probably heard of that commit to RAM and get their durability from committing to multiple replicas in distinct failure domains.
- thesz 5y ago
  300ns is a latency of PCIe, not DRAM. DDR4 CAS latency is 15 clocks, which is about 9ns for highest clock frequency. Add to that cache latencies and memory controller latencies and you easily can get about 25-50 ns of latency and more. And to overcome that you have to use stream-friendly algorithms just as with SSD and spinning disks. The technology of persistent memory is no different than NAND or whateger SSD tech de jour is used. This means that wear will be same as with other SSD drives and may be even worse due to different abmient temperature conditions. Persistent memory is also more expensive. The conflicting transactions must be ordered as if they were processed serially, the actual processing order can be different and their committment to disk also can be different than "commit transaction1 and then commit transaction 2". Having these two transactions commit at once or none at all is also permitted by serializable isolation order. Which is heavily used in any semidecent transactional storage engine. If you go all-in to persistent memory, you lose cheaper multi-tier storage opportunity. You can use heavily read-optimized storage structures on the spinning disks, for example, by rearranging writes to these disks using SSDs and just plain old RAM. If I remember correctly, currently spinning disks are 5 times cheaper than SSD and you can either increase bandwidth or storage volume by using them.
SteveNuts 5y ago
Oracle Database supports halting the database state to persistent memory during OS reboot, basically you can pick up right where you left off when the machine comes back up.
- pbalcer 5y ago
  For anyone interested in how databases can benefit from PMem, I suggest watching this fantastic presentation from Oracle's Jia Shi "Under the Hood of an Exadata Transaction – How Did We Harness the Power of Persistent Memory". https://www.youtube.com/watch?v=ertF5ZwCHP0 https://www.youtube.com/watch?v=ertF5ZwCHP0
EvanAnderson 5y ago
I have some affection for the single-level store architecture of thr AS/400 (at least, on paper-- I've never coded for the platform). I wonder if persistent memory could be an enabler for single-level store architecture operating systems and applications on the PC platform.
- spijdar 5y ago
  I don't think hardware is the limiting factor -- OS/400 runs on a pretty standard RISC platform, same POWER chips that run AIX and Linux. Has some special tagged memory extensions, but nothing too radical, and not a hard requirement for a system like it. The hard part is developing software to use it. I don't think you can really port existing OSes and software to use a single-level store environment. It's a different language than the one we speak. Seems this has been a general problem for persistent memory, to really use it 100% you need new software designed for it.

sidibe 5y ago

Persistent memory has some other advantages that make it good for datacenters. Mainly it is faster than SSD and cheaper than DRAM.

dragontamer 5y ago

I don't think Intel really knew what they were going for with Optane / persistent memory. They had an invention, it had a bunch of interesting stats, and they were hoping someone out there would figure out a use. Databases seem like the obvious answer. Persistent memory / Optane is much faster than NAND Flash... but less dense than NAND Flash. Its also slower than DRAM, but more dense, so it sits in between. Whether or not that's useful remains to be seen.

haimez 5y ago
You might use such a thing in database systems for, eg: 1. The write ahead log, for faster I/O than a direct flush to SSD 2. Staging disk cache entries to persistent memory before a planned host/process restart for faster subsequent DRAM cache warming The problem with 1 is that you still need to periodically flush to disk (at least once persistent storage is full) which means it’s only an improvement in burst activity and not peak throughput. The problem with both is complexity of implementation to deliver functionality that can only be used on a (currently) relatively uncommon subset of servers. Probably not something that Postgres would rush to implement, but potentially something that MSSQL or Oracle might consider as a premium feature. Disclaimer: I haven’t looked into the details of optane and how you interface with that storage in software.

benlivengood 5y ago

Transactional workloads (databases, pubsubs, workflow coordinators) benefit the most from persistent memory because write latency to storage dominates performance (a transaction must be committed to permanent storage before the client can be informed of success, and if there is contention between transactions they must wait and proceed serially). Persistent memory is about 100 times faster (300ns vs. 30us latency) than NAND and is writeable in-place at byte granularity vs. multi-KB erasable blocks.

jeffbee 5y ago
> transaction must be committed to permanent storage before the client can be informed of success Transactions must be durable, but that doesn't mean they can't be committed to RAM initially. There are large-scale database systems you have probably heard of that commit to RAM and get their durability from committing to multiple replicas in distinct failure domains.
thesz 5y ago
300ns is a latency of PCIe, not DRAM. DDR4 CAS latency is 15 clocks, which is about 9ns for highest clock frequency. Add to that cache latencies and memory controller latencies and you easily can get about 25-50 ns of latency and more. And to overcome that you have to use stream-friendly algorithms just as with SSD and spinning disks. The technology of persistent memory is no different than NAND or whateger SSD tech de jour is used. This means that wear will be same as with other SSD drives and may be even worse due to different abmient temperature conditions. Persistent memory is also more expensive. The conflicting transactions must be ordered as if they were processed serially, the actual processing order can be different and their committment to disk also can be different than "commit transaction1 and then commit transaction 2". Having these two transactions commit at once or none at all is also permitted by serializable isolation order. Which is heavily used in any semidecent transactional storage engine. If you go all-in to persistent memory, you lose cheaper multi-tier storage opportunity. You can use heavily read-optimized storage structures on the spinning disks, for example, by rearranging writes to these disks using SSDs and just plain old RAM. If I remember correctly, currently spinning disks are 5 times cheaper than SSD and you can either increase bandwidth or storage volume by using them.

SteveNuts 5y ago

Oracle Database supports halting the database state to persistent memory during OS reboot, basically you can pick up right where you left off when the machine comes back up.

pbalcer 5y ago
For anyone interested in how databases can benefit from PMem, I suggest watching this fantastic presentation from Oracle's Jia Shi "Under the Hood of an Exadata Transaction – How Did We Harness the Power of Persistent Memory". https://www.youtube.com/watch?v=ertF5ZwCHP0 https://www.youtube.com/watch?v=ertF5ZwCHP0

EvanAnderson 5y ago

I have some affection for the single-level store architecture of thr AS/400 (at least, on paper-- I've never coded for the platform). I wonder if persistent memory could be an enabler for single-level store architecture operating systems and applications on the PC platform.

spijdar 5y ago
I don't think hardware is the limiting factor -- OS/400 runs on a pretty standard RISC platform, same POWER chips that run AIX and Linux. Has some special tagged memory extensions, but nothing too radical, and not a hard requirement for a system like it. The hard part is developing software to use it. I don't think you can really port existing OSes and software to use a single-level store environment. It's a different language than the one we speak. Seems this has been a general problem for persistent memory, to really use it 100% you need new software designed for it.