Benchmarking¶ ↑

Environment¶ ↑

The machine running tests is Linux CentOS 2.6.18-194.32.1.el5xen #1 SMP with Quad Core Xeon X3360 @ 2.83GHz, 4GB RAM.

Postgres server version: 9.0.3 Postgres pqlib version: 9.3

Fully Asynchronous vs. poor man’s async¶ ↑

The following {file:benchmarks/em_pg.rb benchmark} compares fully asynchronous implementation (em-pg-client) versus blocking em-pg drivers.

The goal of the test is to retrieve (~80000) rows from the same table with a lot of text data, in chunks, using parallel connections.

The parallel method uses synchrony for simplicity.

• single is (eventmachine-less) job for retrieving a whole data table in one simple query “select * from resources”

• parallel chunk_row_count / concurrency] uses em-pg-client for retrieving result in chunks by chunk_row_count rows and using concurrency parallel connections

• blocking chunk_row_count / concurrency is similiar to parallel except that it uses special patched version of library that uses blocking PGConnection methods

>> benchmark 1000
                              user     system      total        real
    single:              80.970000   0.350000  81.320000 (205.592592)

    parallel 90000/1:    87.380000   0.710000  88.090000 (208.171564)
    parallel 5000/5:     84.250000   3.760000  88.010000 (141.031289)
    parallel 2000/10:    90.190000   4.970000  95.160000 (152.844950)
    parallel 1000/20:    97.070000   5.390000 102.460000 (212.358631)

    blocking 90000/1:    93.590000   0.610000  94.200000 (230.190776)
    blocking 5000/5:     79.930000   1.810000  81.740000 (223.342432)
    blocking 2000/10:    76.990000   2.820000  79.810000 (225.347169)
    blocking 1000/20:    78.790000   3.230000  82.020000 (225.949107)

As we can see the gain from using asynchronous em-pg-client while using parallel queries is noticeable (up to ~30%).

The blocking client however doesn’t gain much from parallel execution. This was expected because it freezes eventmachine until the whole dataset is consumed by the client.

Threads vs. Fibers Streaming Benchmark¶ ↑

The following {file:benchmarks/single_row_mode.rb benchmark} compares performance of parallel running threads using vanilla PG::Connection driver versus EventMachine driven parallel Fibers using PG::EM::Client v0.3.2.

Each thread/fiber retrieves first 5000 rows from the same table with a lot of text data in a single_row_mode. After 5000 rows is retrieved the connection is being reset. The process is repeated after all parallel running threads/fibers finish their task.

Both Thread and Fiber versions use the same chunk of code to retrieve rows.

>> benchmark 400
                               user     system      total        real
    threads 400x1:        24.970000   1.090000  26.060000 ( 30.683818)
    threads 80x5:         24.730000   7.020000  31.750000 ( 51.402710)
    threads 40x10:        22.880000   7.460000  30.340000 ( 52.548910)
    threads 20x20:        22.220000   7.130000  29.350000 ( 53.911111)
    threads 10x40:        22.570000   7.620000  30.190000 ( 54.111841)

    fibers  400x1:        26.040000   1.060000  27.100000 ( 31.619598)
    fibers  80x5:         28.690000   1.140000  29.830000 ( 33.025573)
    fibers  40x10:        28.790000   1.280000  30.070000 ( 33.498418)
    fibers  20x20:        29.100000   1.210000  30.310000 ( 33.289344)
    fibers  10x40:        29.220000   1.340000  30.560000 ( 33.691188)

AxB - repeat A times running B parallel threads/fibers.