Implications of Storage Class Memories (SCMs) on Software Architectures

C. Mohan, IBM Almaden Research Center


Abstract:
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Flash memories have been in widespread usage for a while but they have had 
some performance and reliability problems which have made them unsuitable 
for long term storage of traditional database data. A new class of memory 
called Storage Class Memories (SCMs) are emerging which are built using 
different technologies than flash devices. SCMs overcome many of the 
shortcoming of flash devices while approaching the cost of flash memories. 
SCMs fall in between DRAM and traditional disk storage along many 
dimensions (performance, cost, energy usage, ....). As a result, large 
SCM-based memory systems will be built. While main memory database 
management systems (MMDBMSs) companies like TimesTen and SolidDB have been 
around for a while, those companies have been acquired recently by Oracle 
and IBM, respectively. SCMs will permit the sizes of databases managed by 
MMDBMSs to be very large while being cheaper than those using only DRAMs. 
SCMs may be viewed as disks or as memory from an architectural 
perspective. Depending on the viewpoint, the implications on DBMS 
architectures will be very different. Some preliminary ideas on usage of a 
small amount of non-volatile memory realized by using battery-backed DRAM 
was presented in a paper design called Safe RAM in VLDB 1989. Technology 
has evolved tremendously in 2 decades and it is time for us to revisit 
system architectures.

In IBM Research, we are currently working on a project to understand the 
implications of SCMs on software architectures in general and on DBMS 
architectures in particular. I have worked in the past on the ARIES family 
of recovery and locking algorithms, and in proposing and exploiting, for 
DB2, shared, non-volatile and page addressable store in the IBM mainframe 
parallel sysplex environment. Those ideas would need to be extended to 
take advantage of SCMs. At HPTS 2009, I would like to give a talk on what 
we have learnt from our investigations and what needs to be further 
explored. I believe this presentation will generate a lot of discussions 
and debates. I believe this will be a timely topic for the workshop and 
very suited given the nature of the workshop. I have attended all editions 
of the workshop except, unfortunately, the last one!