The document discusses the benefits of persistent memory in overcoming performance limitations related to disk writes and data management. It presents experimental results demonstrating a significant increase in throughput and a reduction in response time when utilizing persistent memory, highlighting its potential advantages for systems like HBase. Additionally, it addresses current software support and outlines potential solutions to achieve higher bandwidth with lower latency in data transactions.

1. Breaking the Sound Barrier with Persistent Memory
Liqi Yi
Shylaja Kokoori

2. Legal Disclaimer
2
Intel may make changes to specifications and product descriptions at any time, without notice. Designers must not rely on the absence or characteristics of
any features or instructions marked "reserved" or "undefined". Intel reserves these for future definition and shall have no responsibility whatsoever for
conflicts or incompatibilities arising from future changes to them. The information here is subject to change without notice. Do not finalize a design with
this information.
The products described in this document may contain design defects or errors known as errata which may cause the product to deviate from published
specifications. Current characterized errata are available on request.
Contact your local Intel sales office or your distributor to obtain the latest specifications and before placing your product order.
Tests document performance of components on a particular test, in specific systems. Differences in hardware, software, or configuration will affect actual
performance. Consult other sources of information to evaluate performance as you consider your purchase.
For more complete information about performance and benchmark results, visit http://www.intel.com/performance.
Results have been estimated based on internal Intel analysis and are provided for informational purposes only. Any difference in system hardware or
software design or configuration may affect actual performance.
Results have been simulated and are provided for informational purposes only. Results were derived using simulations run on an architecture simulator or
model. Any difference in system hardware or software design or configuration may affect actual performance.
Intel does not control or audit the design or implementation of third party benchmark data or Web sites referenced in this document. Intel encourages all
of its customers to visit the referenced Web sites or others where similar performance benchmark data are reported and confirm whether the referenced
benchmark data are accurate and reflect performance of systems available for purchase.
Intel and the Intel logo are trademarks of Intel Corporation in the U.S. and other countries.
*Other names and brands may be claimed as the property of others.
Copyright © 2016 Intel Corporation. All rights reserved.

3. Motivation
 Disk writes not uniform
 Disk writes happen in burst fashion, and high write bandwidth is
required while flushing & compacting
 Read/write bandwidth inflation
 Each Key/Value (KV) pair will be written to disk and read back many
times due to flush, compact, and read caching. This inflation is
very painful when handling large query rate on a small memory
system.
 Change in data format (serialization/deserialization) between memory
and data store (for example, disk)
 Adds latency to the read/write path, and wastes a lot of CPU
cycles.
3

4. What do we need to by pass these issues
• Persistent store with much higher bandwidth
• Larger cache for data on disk
• Less number of round trips for KVs between memory and persistent
store
• What if we do not need to change the format when sending and bringing
data between memory and data store?
• Of course, lower latency always helps !!
4

5. Do we have something that fulfills these
requirements?
 PCI-E SSD (NVM)
 Faster than SATA SSD, but much slower than memory(both latency and
bandwidth), still could be bottle necked on heavy load, still needs
to do data format changing
 Huge DRAM
 Ideal case, solves everything, but way to expensive, and subject to
data loss
 What if we can put persistency and memory together?
5

6. Do we have something that fulfills these
requirements?
 PCI-E SSD (NVM)
 Faster than SATA SSD, but much slower than memory(both latency and
bandwidth), //still could be bottle necked on heavy load, still
needs to do data format changing) //make it a table
 Huge DRAM
 Ideal case, solves everything, but way to expensive, and subject to
data loss
 What if we can put persistency and memory together?
6
The solution: Persistent Memory

7. Experiment Setup
• Persistent memory emulation environment was used to emulate the
latencies of persistent memory. This environment is capable of
performing at varied latencies.
• Used Yahoo Cloud Serving Benchmark(YCSB) to drive the HBase cluster
• Number of query/transaction per second used to measure throughput
• Round trip time for the query was used to measure latency
• Database was preloaded and experiment involved pure read
• In baseline configuration, if data is not available in DRAM it is
read from SSDs
7

8. Experiment Design
Experiment was designed around following scenarios
• Increase Bucket Cache on persistent memory at regular percentage
increment (10%) and observe the effect on throughput and response
time
• Restrict the input transaction count and observe the effect on
throughput and response time for baseline and 100% bucket cache on
persistent memory
• Change persistent memory latency and observe its impact on response
time
8

9. Approximately 5x increase in throughput when all the
bucket cache is configured in persistent memory
6.8 7.2 7.6 8.4 9.7 11.2
13.4
16.5
21.2
28.6
40.4
0% 10% 20% 30% 40% 50% 60% 70% 80% 90% 100% 110%
Kops/sec
Bucket cache % configured in persistent memory
Change in throughput as percentage of bucket cache
configured in persistent memory
5x increase

10. Change in query response time as percentage of
bucket cache moved to persistent memory
29.4
27.7
26.1
23.9
20.4
17.8
14.8
12.1
9.4
7.0
4.9
0% 10% 20% 30% 40% 50% 60% 70% 80% 90% 100% 110%
ms
Bucket cache % configured in persistent memory
Change in average query response time as percentage of bucket cache configured in persistent memory
Approximately 6x reduction in response time when all the
bucket cache is configured in persistent memory
6x

11. Persistent Memory Latency Impact
Latency change between 115ns and 500ns increases YCSB’s client response
time by 1%
11
Persistent memory read latency (ns) 115 200 300 400 500 600
YCSB average response time (ms) 39.0 39.0 40.5 39.6 38.3 37.9
Increased memory latency impact on YCSB
response time (%) 0% 0% 1% 1% 1%

12. Current software support
12
Graph from http://www.snia.org/sites/default/files/NVM/2016/presentations/RickCoulson_All_the_Ways_3D_XPoint_Impacts.pdf
• Open Source:
http://pmem.io
• libvmem, libvmmalloc
• libpmem, libpmemobj,
libpmemblk, libpmemlog

13. Summary
• Persistent memory is faster, larger, with byte addressable
capability.
• HBase will benefit from persistent memory in current architecture and
possibly new architectures in the future.
• Software support is on track.
13