| DiskCache Cache Benchmarks |
| ========================== |
|
|
| Accurately measuring performance is a difficult task. The benchmarks on this |
| page are synthetic in the sense that they were designed to stress getting, |
| setting, and deleting items repeatedly. Measurements in production systems are |
| much harder to reproduce reliably. So take the following data with a `grain of |
| salt`_. A stated feature of :doc:`DiskCache <index>` is performance so we would |
| be remiss not to produce this page with comparisons. |
|
|
| The source for all benchmarks can be found under the "tests" directory in the |
| source code repository. Measurements are reported by percentile: median, 90th |
| percentile, 99th percentile, and maximum along with total time and miss |
| rate. The average is not reported as its less useful in response-time |
| scenarios. Each process in the benchmark executes 100,000 operations with ten |
| times as many sets as deletes and ten times as many gets as sets. |
|
|
| Each comparison includes `Memcached`_ and `Redis`_ with default client and |
| server settings. Note that these backends work differently as they communicate |
| over the localhost network. The also require a server process running and |
| maintained. All keys and values are short byte strings to reduce the network |
| impact. |
|
|
| .. _`grain of salt`: https: |
| .. _`Memcached`: http: |
| .. _`Redis`: http: |
|
|
| Single Access |
| ------------- |
|
|
| The single access workload starts one worker processes which performs all |
| operations. No concurrent cache access occurs. |
|
|
| Get |
| ... |
|
|
| .. image:: _static/core-p1-get.png |
|
|
| Above displays cache access latency at three percentiles. Notice the |
| performance of :doc:`DiskCache <index>` is faster than highly optimized |
| memory-backed server solutions. |
|
|
| Set |
| ... |
|
|
| .. image:: _static/core-p1-set.png |
|
|
| Above displays cache store latency at three percentiles. The cost of writing to |
| disk is higher but still sub-millisecond. All data in :doc:`DiskCache <index>` |
| is persistent. |
|
|
| Delete |
| ...... |
|
|
| .. image:: _static/core-p1-delete.png |
|
|
| Above displays cache delete latency at three percentiles. As above, deletes |
| require disk writes but latency is still sub-millisecond. |
|
|
| Timing Data |
| ........... |
|
|
| Not all data is easily displayed in the graphs above. Miss rate, maximum |
| latency and total latency is recorded below. |
|
|
| ========= ========= ========= ========= ========= ========= ========= ========= |
| Timings for diskcache.Cache |
| ------------------------------------------------------------------------------- |
| Action Count Miss Median P90 P99 Max Total |
| ========= ========= ========= ========= ========= ========= ========= ========= |
| get 88966 9705 12.159us 17.166us 28.849us 174.999us 1.206s |
| set 9021 0 68.903us 93.937us 188.112us 10.297ms 875.907ms |
| delete 1012 104 47.207us 66.042us 128.031us 7.160ms 89.599ms |
| Total 98999 2.171s |
| ========= ========= ========= ========= ========= ========= ========= ========= |
|
|
| The generated workload includes a ~1% cache miss rate. All items were stored |
| with no expiry. The miss rate is due entirely to gets after deletes. |
|
|
| ========= ========= ========= ========= ========= ========= ========= ========= |
| Timings for diskcache.FanoutCache(shards=4, timeout=1.0) |
| ------------------------------------------------------------------------------- |
| Action Count Miss Median P90 P99 Max Total |
| ========= ========= ========= ========= ========= ========= ========= ========= |
| get 88966 9705 15.020us 20.027us 33.855us 437.021us 1.425s |
| set 9021 0 71.049us 100.136us 203.133us 9.186ms 892.262ms |
| delete 1012 104 48.161us 69.141us 129.952us 5.216ms 87.294ms |
| Total 98999 2.405s |
| ========= ========= ========= ========= ========= ========= ========= ========= |
|
|
| The high maximum store latency is likely an artifact of disk/OS interactions. |
|
|
| ========= ========= ========= ========= ========= ========= ========= ========= |
| Timings for diskcache.FanoutCache(shards=8, timeout=0.010) |
| ------------------------------------------------------------------------------- |
| Action Count Miss Median P90 P99 Max Total |
| ========= ========= ========= ========= ========= ========= ========= ========= |
| get 88966 9705 15.020us 20.027us 34.094us 627.995us 1.420s |
| set 9021 0 72.956us 100.851us 203.133us 9.623ms 927.824ms |
| delete 1012 104 50.783us 72.002us 132.084us 8.396ms 78.898ms |
| Total 98999 2.426s |
| ========= ========= ========= ========= ========= ========= ========= ========= |
|
|
| Notice the low overhead of the :class:`FanoutCache |
| <diskcache.FanoutCache>`. Increasing the number of shards from four to eight |
| has a negligible impact on performance. |
|
|
| ========= ========= ========= ========= ========= ========= ========= ========= |
| Timings for pylibmc.Client |
| ------------------------------------------------------------------------------- |
| Action Count Miss Median P90 P99 Max Total |
| ========= ========= ========= ========= ========= ========= ========= ========= |
| get 88966 9705 25.988us 29.802us 41.008us 139.952us 2.388s |
| set 9021 0 27.895us 30.994us 40.054us 97.990us 254.248ms |
| delete 1012 104 25.988us 29.087us 38.147us 89.169us 27.159ms |
| Total 98999 2.669s |
| ========= ========= ========= ========= ========= ========= ========= ========= |
|
|
| Memcached performance is low latency and stable. |
|
|
| ========= ========= ========= ========= ========= ========= ========= ========= |
| Timings for redis.StrictRedis |
| ------------------------------------------------------------------------------- |
| Action Count Miss Median P90 P99 Max Total |
| ========= ========= ========= ========= ========= ========= ========= ========= |
| get 88966 9705 44.107us 54.121us 73.910us 204.086us 4.125s |
| set 9021 0 45.061us 56.028us 75.102us 237.942us 427.197ms |
| delete 1012 104 44.107us 54.836us 72.002us 126.839us 46.771ms |
| Total 98999 4.599s |
| ========= ========= ========= ========= ========= ========= ========= ========= |
|
|
| Redis performance is roughly half that of Memcached. :doc:`DiskCache <index>` |
| performs better than Redis for get operations through the Max percentile. |
|
|
| Concurrent Access |
| ----------------- |
|
|
| The concurrent access workload starts eight worker processes each with |
| different and interleaved operations. None of these benchmarks saturated all |
| the processors. |
|
|
| Get |
| ... |
|
|
| .. image:: _static/core-p8-get.png |
|
|
| Under heavy load, :doc:`DiskCache <index>` gets are low latency. At the 90th |
| percentile, they are less than half the latency of Memcached. |
|
|
| Set |
| ... |
|
|
| .. image:: _static/core-p8-set.png |
|
|
| Stores are much slower under load and benefit greatly from sharding. Not |
| displayed are latencies in excess of five milliseconds. With one shard |
| allocated per worker, latency is within a magnitude of memory-backed server |
| solutions. |
|
|
| Delete |
| ...... |
|
|
| .. image:: _static/core-p8-delete.png |
|
|
| Again deletes require writes to disk. Only the :class:`FanoutCache |
| <diskcache.FanoutCache>` performs well with one shard allocated per worker. |
|
|
| Timing Data |
| ........... |
|
|
| Not all data is easily displayed in the graphs above. Miss rate, maximum |
| latency and total latency is recorded below. |
|
|
| ========= ========= ========= ========= ========= ========= ========= ========= |
| Timings for diskcache.Cache |
| ------------------------------------------------------------------------------- |
| Action Count Miss Median P90 P99 Max Total |
| ========= ========= ========= ========= ========= ========= ========= ========= |
| get 712546 71214 15.974us 23.127us 40.054us 4.953ms 12.349s |
| set 71530 0 94.891us 1.328ms 21.307ms 1.846s 131.728s |
| delete 7916 807 65.088us 1.278ms 19.610ms 1.244s 13.811s |
| Total 791992 157.888s |
| ========= ========= ========= ========= ========= ========= ========= ========= |
|
|
| Notice the unacceptably high maximum store and delete latency. Without |
| sharding, cache writers block each other. By default :class:`Cache |
| <diskcache.Cache>` objects raise a timeout error after sixty seconds. |
|
|
| ========= ========= ========= ========= ========= ========= ========= ========= |
| Timings for diskcache.FanoutCache(shards=4, timeout=1.0) |
| ------------------------------------------------------------------------------- |
| Action Count Miss Median P90 P99 Max Total |
| ========= ========= ========= ========= ========= ========= ========= ========= |
| get 712546 71623 19.073us 35.048us 59.843us 12.980ms 16.849s |
| set 71530 0 108.004us 1.313ms 9.176ms 333.361ms 50.821s |
| delete 7916 767 73.195us 1.264ms 9.033ms 108.232ms 4.964s |
| Total 791992 72.634s |
| ========= ========= ========= ========= ========= ========= ========= ========= |
|
|
| Here :class:`FanoutCache <diskcache.FanoutCache>` uses four shards to |
| distribute writes. That reduces the maximum latency by a factor of ten. Note |
| the miss rate is variable due to the interleaved operations of concurrent |
| workers. |
|
|
| ========= ========= ========= ========= ========= ========= ========= ========= |
| Timings for diskcache.FanoutCache(shards=8, timeout=0.010) |
| ------------------------------------------------------------------------------- |
| Action Count Miss Median P90 P99 Max Total |
| ========= ========= ========= ========= ========= ========= ========= ========= |
| get 712546 71106 25.034us 47.922us 101.089us 9.015ms 22.336s |
| set 71530 39 134.945us 1.324ms 5.763ms 16.027ms 33.347s |
| delete 7916 775 88.930us 1.267ms 5.017ms 13.732ms 3.308s |
| Total 791992 58.991s |
| ========= ========= ========= ========= ========= ========= ========= ========= |
|
|
| With one shard allocated per worker and a low timeout, the maximum latency is |
| more reasonable and corresponds to the specified 10 millisecond timeout. Some |
| set and delete operations were therefore canceled and recorded as cache |
| misses. The miss rate due to timeout is about 0.01% so our success rate is |
| four-nines or 99.99%. |
|
|
| ========= ========= ========= ========= ========= ========= ========= ========= |
| Timings for pylibmc.Client |
| ------------------------------------------------------------------------------- |
| Action Count Miss Median P90 P99 Max Total |
| ========= ========= ========= ========= ========= ========= ========= ========= |
| get 712546 72043 83.923us 107.050us 123.978us 617.027us 61.824s |
| set 71530 0 84.877us 108.004us 124.931us 312.090us 6.283s |
| delete 7916 796 82.970us 105.858us 123.024us 288.963us 680.970ms |
| Total 791992 68.788s |
| ========= ========= ========= ========= ========= ========= ========= ========= |
|
|
| Memcached performance is low latency and stable even under heavy load. Notice |
| that cache gets are three times slower in total as compared with |
| :class:`FanoutCache <diskcache.FanoutCache>`. The superior performance of get |
| operations put the overall performance of :doc:`DiskCache <index>` ahead of |
| Memcached. |
|
|
| ========= ========= ========= ========= ========= ========= ========= ========= |
| Timings for redis.StrictRedis |
| ------------------------------------------------------------------------------- |
| Action Count Miss Median P90 P99 Max Total |
| ========= ========= ========= ========= ========= ========= ========= ========= |
| get 712546 72093 138.044us 169.039us 212.908us 151.121ms 101.197s |
| set 71530 0 138.998us 169.992us 216.007us 1.200ms 10.173s |
| delete 7916 752 136.137us 167.847us 211.954us 1.059ms 1.106s |
| Total 791992 112.476s |
| ========= ========= ========= ========= ========= ========= ========= ========= |
|
|
| Redis performance is roughly half that of Memcached. Beware the impact of |
| persistence settings on your Redis performance. Depending on your use of |
| logging and snapshotting, maximum latency may increase significantly. |
|
|
