Boost Write Performance for DBMS on Solid State Drive

Yu LI

Backgrounds (1)

SSD is a complex storage device flash chips (i.e., NAND) controller hardware proprietary software (i.e., firmware) block device interface via a standard

interconnect (e.g., USB, IDE, SATA). In general:

Sequential read/write, random read is fast. Random write is slow.

Backgrounds (2)

Some DBMS applications trend to generate random write stream Online Transaction Processing (OLTP)

Small and frequent insert/delete/update Concurrence

In-Page Logging Approach

In-Page Logging Approach [Lee, Sigmod 07]

Idea: turn random write to log appending

However In-page logging area nee

ds hardware support. For SSD, not practical.

Backgrounds (3)

Question: is there any solution to improve write performance without modifying the firmware of SSD ?

Systemetic performance studies show that not all kinds of “random write” on SSD are slow.

Write performance depends more on write pattern on SSD. [uFlip CIDR2009]

uFlip resultsFocused write

e.g., write inside a <8MB file

Partitioned Sequential Write writee.g., 1,50,2,51,3,52,…

Ordered Sequential Write writee.g., 1,3,5,7,9,…

Our Idea (1)

Write StreamDecomposition

If we can collect enough write requests:

• Isolate the write request of good write patterns

• Cluster write requests to form instance of focused write

SSD

Our Idea (2)

StableBuffer1

3

SSD

Decomposition 2

Through StableBuffer:• Two writes (1,3) in good write pattern

(1x~4x)• One random read (2) (at most 1x)=> Total 9x

Directly:=> 17x~30x

StableBuffer

DBMS Buffer ManagerDBMS

Transactions

StableBuffer Translation Table

Write

Write Stream Decompositors

Main Memory SSD

Write

Read

System Overview

Components of StableBuffer Manager

StableBuffer: pre-allocated focused are on SSD. E.g., pre-allocated file < 8MB.

StableBuffer Translation Table: A table for entries like “<12345678AB, 32>” Fast lookup, insert and delete

Write Stream Decompositors: A group programs running in concurrent threads Decomposite instance of good write pattern

More on StableBuffer Translation Table

Reverse index embedded in pages for StableBuffer Translation Table Destinations and timestamp For recovery in case of system crush

When recovery, page at offset O whose destination is D, compare its timestamp T to the latest update time T0 of page at destination D If T> T0 , insert <D,O> into table. Otherwise, the slot O is free.

Query on StableBuffer

When get a request of retrieving some page at D we need to check whether there is an entry “<D,

O>” in StableBuffer Translation Table. If there is, return page at Oth slot in StableBuffer. Otherwise issue a read request to SSD for the page at

D.

So it is better to implement StableBuffer Translation Table as a hash table on D.

index

Sequential Write Stream

Partitioned Sequential Write Stream

Focused Write Stream

StableBuffer Translation Table

Decomposite

Sequential Write Decompositor

Petitioned Sequential Write Decompositor

Focused Write Decompositor

Decompositors

Share

Ordered Sequential Write Stream

Ordered Sequential Write Decompositor

Share

index

index

index

Decompositors (1)

Decompositors (2)

Decompositors run in concurrent threads. The results could share same entries of StableB

uffer Translation Table. Select the results of decompositors

select the instance of write pattern which performs better on SSD.

select bigger instance. E.g., 1,2,56,57,6,7,42,43,3,4,...

We select the results according to

}min{i

i

L

T

Decompositors (3)

Sequential Write Decompositor Maintain a search tree index on the destination addresses

of mapping entries Partitioned Write Decompositor

share the search tree index of Sequential Write Decompositor

Ordered Write Decompositor share the search tree index of Sequential Write Decompo

sitor Focused Write Decompositor

maintains a hash index of entries of StableBuffer TranslationTable. entry “< D;O >” will be hashed into bucket MD /

Preliminary Result of Evaluation

Prototype of StableBuffer manager Accept write trace file On Windows desktop pc, 16GB MTron MSD-SATA-3525

SSD page size 4KB StableBuffer is 8MB = 2048 pages

Trace Oracle 11g running TPC-C benchmark simulates an enterprise OLTP retailing system, which kee

ping insert/delete/update records from a 8GB database 488623 write requests

Preliminary Result of Evaluation

0

0.5

1

1.5

2

2.5

3

Direct StableBuffer

Ban

dwid

th (M

B/s

)

1.5x

Q & A

Thanks