PG-Strom - GPGPU meets PostgreSQL, PGcon2015

1
PG-Strom
~GPGPU meets PostgreSQL~
NEC Business Creation Division
The PG-Strom Project
KaiGai Kohei <kaigai@ak.jp.nec.com>

2
About me
▌About PG-Strom project
 The 1st prototype was unveiled at Jan-2012,
based on personal interest
 Now, it became NEC internal startup project.
▌Who are you
 Name: KaiGai Kohei
 Works: NEC
 Roles:
• development of software
• development of business
 Past contributions:
• SELinux integration (sepgsql) and various
security stuff
• Writable FDW & Remote Join Infrastructure
• ...and so on
PGconf2015 / PG-Strom - GPGPU meets PostgreSQL

3
Parallel Database is fun!
▌Growth of data size
▌Analytics makes values hidden in data
▌Price reduction of parallel processors
All the comprehensives requires database be parallel

4
Approach to Parallel Database
Scale-out
Scale-Up Homogeneous Scale-Up
Heterogeneous Scale-Up
+

5
Why GPU?
No Free Lunch for Software, by Hardware
▌Power consumption & Dark silicon problem
▌Heterogeneous architecture
▌Software has to be designed to pull out full capability of
the modern hardware
SOURCE: THE HEART OF AMD INNOVATION,
Lisa Su, at AMD Developer Summit 2013
SOURCE: Compute Power with Energy-Efficiency,
Jem Davies, at AMD Fusion Developer Summit 2011

6
Features of GPU (Graphic Processor Unit)
▌Massive parallel cores
▌Much higher DRAM bandwidth
▌Better price / performance ratio
▌Advantage
Simple arithmetic operations
Agility in multi-threading
▌Disadvantage
complex control logic
no operating system
SOURCE: CUDA C Programming Guide
GPU CPU
Model
Nvidia GTX
TITAN X
Intel Xeon
E5-2690 v3
Architecture Maxwell Haswell
Launch Mar-2015 Sep-2014
# of transistors 8.0billion 3.84billion
# of cores
3072
(simple)
12
(functional)
Core clock 1.0GHz
2.6GHz,
up to 3.5GHz
Peak Flops
(single
precision)
6.6TFLOPS
998.4GFLOPS
(with AVX2)
DRAM size
12GB, GDDR5
(384bits bus)
768GB/socket,
DDR4
Memory band 336.5GB/s 68GB/s
Power
consumption
250W 135W
Price $999 $2,094

7
How GPU cores works
●item[0]
step.1 step.2 step.4step.3
Calculation of
𝑖𝑡𝑒𝑚[𝑖]
𝑖=0…𝑁−1
with GPU cores
◆
●
▲ ■ ★
● ◆
●
● ◆ ▲
●
● ◆
●
● ◆ ▲ ■
●
● ◆
●
● ◆ ▲
●
● ◆
●
item[1]
item[2]
item[3]
item[4]
item[5]
item[6]
item[7]
item[8]
item[9]
item[10]
item[11]
item[12]
item[13]
item[14]
item[15]
Sum of items[]
by log2N steps
Inter-core synchronization by HW functionality

8
What is PG-Strom (1/2) – Core ideas
▌Core idea
① GPU native code generation on the fly
② Asynchronous execution and pipelining
▌Advantage
 Transparent acceleration with 100% query compatibility
 Heavy query involving relations join and/or aggregation
Parser
Planner
Executor
Custom-
Scan/Join
Interface
Query: SELECT * FROM l_tbl JOIN r_tbl on l_tbl.lid = r_tbl.rid;
PG-Strom
CUDA
driver
nvrtc
DMA Data Transfer
CUDA
Source
code
Massive
Parallel
Execution

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What is PG-Strom (2/2) – Beta functionality at Jun-2015
▌Logics
 GpuScan ... Simple loop extraction by GPU multithread
 GpuHashJoin ... GPU multithread based N-way hash-join
 GpuNestLoop ... GPU multithread based N-way nested-loop
 GpuPreAgg ... Row reduction prior to CPU aggregation
 GpuSort ... GPU bitonic + CPU merge, hybrid sorting
▌Data Types
 Numeric ... int2/4/8, float4/8, numeric
 Date and Time ... date, time, timestamp, timestamptz
 Text ... Only uncompressed inline varlena
▌Functions
 Comparison operator ... <, <=, !=, =, >=, >
 Arithmetic operators ... +, -, *, /, %, ...
 Mathematical functions ... sqrt, log, exp, ...
 Aggregate functions ... min, max, sum, avg, stddev, ...

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CustomScan Interface (v9.5 new feature)
set_rel_pathlist()
 set_rel_pathlist_hook
add_paths_to_joinrel()
 set_join_pathlist_hook
SeqScan
Index
Scan
Custom
Scan
(GpuScan)
HashJoin NestLoop
Custom
Scan
(GpuJoin)
PlannedStmt
PlanTree
with
Custom
Logic

11
GPU code generation and JIT compile
postgres=# SELECT cat, AVG(x) FROM t0
WHERE sqrt((x-20)^2 + (y-10)^2) < 5
GROUP BY cat;
STATIC_FUNCTION(bool)
gpupreagg_qual_eval(cl_int *errcode,
kern_parambuf *kparams,
kern_data_store *kds,
kern_data_store *ktoast,
size_t kds_index)
{
pg_float8_t KPARAM_1 = pg_float8_param(kparams,errcode,1);
pg_float8_t KVAR_8 = pg_float8_vref(kds,errcode,7,kds_index);
pg_float8_t KVAR_9 = pg_float8_vref(kds,errcode,8,kds_index);
return EVAL(pgfn_float8lt(errcode,pgfn_dsqrt(errcode,
pgfn_float8pl(errcode, pgfn_dpow(errcode, pgfn_float8mi(errcode,
KVAR_8, KPARAM_1), KPARAM_2), pgfn_dpow(errcode,
pgfn_float8mi(errcode, KVAR_9, KPARAM_3), KPARAM_4))),
KPARAM_5));
}
CUDA runtime compiler
(nvrtc; CUDA7.0 or later)
nvrtcCompileProgram(...)
CUDA runtime
.ptx
GPU
binary
Massive
Parallel
Execution

12
(OT) How to combine static and dynamic code
STATIC_FUNCTION(cl_uint)
gpujoin_hash_value(cl_int *errcode,
kern_parambuf *kparams,
cl_uint *pg_crc32_table,
kern_multirels *kmrels,
cl_int depth,
cl_int *outer_index);
GpuScan
GpuJoin
GpuPreAgg
GpuSort
CustomScan
Providers
KERNEL_FUNCTION(void)
gpujoin_exec_hashjoin(kern_gpujoin *kgjoin,
kern_multirels *kmrels,
cl_int depth,
cl_int cuda_index,
cl_bool *outer_join_map)
{
:
hash_value = gpujoin_hash_value(&errcode,
kparams,
pg_crc32_table,
kds,
kmrels,
depth,
x_buffer);
:
is_matched = gpujoin_join_quals(&errcode,
kparams,
kds,
kmrels,
depth,
x_buffer,
h_htup);
cuda_
program.c
.ptx
GPU
binary
Dynamic
Portion
Static
Portion

13
How GPU Logic works (1/2) – Case of GpuScan
kern_data_store
(DMA Buffer)
kern_data_store
(On GPU RAM)
●●●●●●●●
CustomScan
(GpuScan)
CUmodule
② Load to DMA buffer
(100K~500K Rows/buffer)
③ Kick Asynchronous
DMA over PCI-E
RelOptInfo
baserestrictinfo
① GPU code generation
& JIT compile
④ Launch GPU
kernel function
Each GPU core
evaluate each rows
in parallel
⑤ Write back
results

14
Asynchronous Execution and Pipelining
DMA
Send
GPU
Kernel
Exec
DMA
Recv
DMA
Send
GPU
Kernel
Exec
DMA
Recv
DMA
Send
GPU
Kernel
Exec
DMA
Recv
DMA
Send
GPU
Kernel
Exec
tablescan
Buffer
Read
Buffer
Read
Buffer
Read
Buffer
Read
Move
to next
Move
to next
chunk-(i+1)
chunk-(i+2)
chunk-i
chunk-(i+3)
Current
Task
Current
Task
Current
Task
Current
Task
Current
Task
Current
Task

15
How GPU Logic works (2/2) – Case of GpuNestLoop
Outer-Relation
(Nx:usuallylarger)
※splittochunk-by-chunkon
demand
●
●
●
●
●
●
●
●
●
●
●●●●●●●Two
dimensional
GPU kernel
launch
blockDim.x
blockDim.y
Ny
Nx
Thread
(X=2, Y=3)
Inner-Relation
(Ny: relatively small)
Only edge thread references
DRAM to fetch values.
Nx:32 x Ny:32 = 1024
A matrix can be evaluated with
only 64 times DRAM accesses

16
Benchmark Results (1/2) – Microbenchmark
▌SELECT cat, AVG(x) FROM t0 NATURAL JOIN t1 [, ...] GROUP BY cat;
measurement of query response time with increasing of inner relations
▌t0: 100M rows, t1~t10: 100K rows for each, all the data was preloaded.
▌PostgreSQL v9.5devel + PG-Strom (26-Mar), CUDA 7(x86_64)
▌CPU: Xeon E5-2640, RAM: 256GB, GPU: NVIDIA GTX980
81.71
122.96
165.05
214.64
261.51
307.18
356.20
406.59
468.59
520.45
8.38 9.02 8.84 10.33 11.47 13.21
14.48 17.15 19.37 21.72
0
100
200
300
400
500
600
1 2 3 4 5 6 7 8 9 10
QueryExecutionTime[sec]
number of tables joined
PostgreSQL PG-Strom

17
Benchmark Results (2/2) – DBT-3 with SF=20
▌PostgreSQL v9.5devel + PG-Strom (26-Mar), CUDA 7(x86_64)
▌CPU: Xeon E5-2640, RAM: 256GB, GPU: NVIDIA GTX980
PG-Strom is almost faster than PostgreSQL, up to x10 times(!)
Q21 result is missing because of too large memory allocation by nodeHash.c
0
20
40
60
80
100
120
140
160
Q1 Q2 Q3 Q4 Q5 Q6 Q7 Q8 Q9 Q10 Q11 Q12 Q13 Q14 Q15 Q16 Q17 Q18 Q19 Q20 Q22
QueryResponseTime[sec]
Comparison by DBT-3 Benchmark (SF=20)
PostgreSQL PG-Strom

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(OT) Why columnar-format is ideal for GPU
▌Reduction of I/O workload
▌Higher compression ratio
▌Less amount of DMA transfer
▌Suitable for SIMD operation
▌Maximum performance on GPU kernel,
by coalesced memory access
SOURCE: Maxwell: The Most Advanced CUDA GPU Ever Made
Core Core Core Core Core Core Core Core Core Core
coalesced memory access
Global Memory (DRAM)
Wide
Memory
Bandwidth
(256-
384bits)
WARP:
Unit of GPU threads
that share
instruction pointer

19
(OT) Why PG-Strom (at this moment) use row-format
▌Future direction
 Integration with native columnar storage
 Column  Row translation in GPU space
storage
columnar
cache
Tuple
TableSlot
RowColumn
(only once)
ColumnRow
(per execution)
Catastrophic
CPU cycle
consumption
(T_T)
Ideal
Performance
（^-^）
Not fast, but
only once
（´へ｀）

20
Expected Scenario (1/2) – Backend of business intelligence
▌Reduction of DBA work-loads/burden
▌A new option for database tuning
▌Analytics under the operation
ERPCRMSCM BI
OLTP
database
OLAP
database
ETL
OLAP CubesMaster / Fact Tables
PG-Strom
+
PG-Strom
+
delay on
translation
carefully designed
with human-
intelligence
periodic
tuning burden

21
Expected Scenario (2/2) – Computing In-Place
▌Computing In-Place
 Why people export data once, to run their algorithm?
RDBMS is not designed as a tool compute stuff
 If RDBMS can intermediate the world of data management
and computing/calculation?
▌All we need to fetch is data already processed
▌System landscape gets simplified
PG-Strom
Extra
Tools
pl/CUDA
function?
Complicated
mathematical logic
on the data exported
future
works

22
Welcome your involvement
▌Early adopters are big welcome
 SaaS provider or ISV on top of PostgreSQL, notably
 Folks who have real-life workloads and dataset
▌Let’s have joint evaluation/development

23
Our sweet spot?
SOURCE: Really Big Elephants – Data Warehousing with PostgreSQL,
Josh Berkus, MySQL User Conference 2011
• Parallel context and scan
• GPU Acceleration (PG-Strom)
• Funnel Executor
• Aggregate Before Join
• Table partitioning & Sharding
• Native columnar storage

24
Our position
WE ARE HERE
SOURCE: The Innovator's Dilemma,
Prof. Clayton Christensen , Harvard Business School

25
Towards v9.6 (1/2) – Aggregation before Join
▌Problem
 All the aggregations are done
on the final stage of execution
▌Solution
 Make a partial aggregate first,
then Join and final aggregate
▌Benefit
 Reduction of Join workloads
 Partial aggregate is sweet spot
of GPU acceleration.
▌Challenge
 Planner enhancement to deal
with various path-nodes
 Aggregate Combined Function
Original Query
Aggregate before Join
Agg
Join
Table-A Table-B
Agg
Join
Table-A Table-B
PreAgg
N=1000 N=1000M
N=1000M
N=1000
N=1000
N=1000
N=1000M
N=1000 sweet spot
of GPU

26
SSD
Towards v9.6 (2/2) – CustomScan under Funnel Executor
▌Problem
 Low I/O density on Scan
 Throughput of input stream
▌Solution
 Split a large chunk into
multiple chunks using BGW
▌Benefit
 Higher I/O density
 CPU+GPU hybrid parallel
▌Challenge
 Planner enhancement to deal
with various path-nodes
 SSD optimization
 CustomScan nodes across
multiple processes
Hash
Join
Outer
Scan
(partial)
Hash
Join
Outer
Scan
(partial)
Inner
Scan
Inner
Scan
HashHash
Funnel
Executor
Gpu
Join
Gpu
Join
Gpu
Scan
(partial)
Gpu
Scan
(partial)
BgWorker-1 BgWorker-N

27
Resources
▌Source
 https://github.com/pg-strom/devel
▌Requirement
 PostgreSQL v9.5devel
 Hotfix patch (custom_join_children.v2.patch)
 CUDA 7.0 provided by NVIDIA
▌On cloud (AWS)
g2.2xlarge
CPU Xeon E5-2670
(8 xCPU)
RAM 15GB
GPU NVIDIA GRID K2
(1536 core)
Storage 60GB of SSD
Price $0.898/hour
(*) Tokyo region, at Jun-2015
strom-ami.20150615
AMI-Id: ami-3e29f23e
or, search by “strom”

PG-Strom - GPGPU meets PostgreSQL, PGcon2015

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