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Diffstat (limited to 'content/posts')
| -rw-r--r-- | content/posts/postgres-aggregation-speed/index.md | 146 |
1 files changed, 121 insertions, 25 deletions
diff --git a/content/posts/postgres-aggregation-speed/index.md b/content/posts/postgres-aggregation-speed/index.md index 2029dd0..0f1efee 100644 --- a/content/posts/postgres-aggregation-speed/index.md +++ b/content/posts/postgres-aggregation-speed/index.md @@ -143,13 +143,31 @@ They look pretty similar. I run these five queries with `EXPLAIN (ANALYZE, COSTS, VERBOSE, BUFFERS)`, and I can note their total time, alongside the different nodes duration in the plan. -| Query | Total | `Seq Scan` | `HashAggregate` | -| -------------- | ------ | ---------- | --------------- | -| `composite` | 80 ms | 39 ms | 40 ms | -| `json array` | 120 ms | 37 ms | 86 ms | -| `jsonb array` | 150 ms | 35 ms | 112 ms | -| `json object` | 160 ms | 40 ms | 120 ms | -| `jsonb object` | 220 ms | 40 ms | 180 ms | +{{< chart type="bar" data=`{ + "labels": ["composite", "json array", "jsonb array", "json object", "jsonb object"], + "datasets": [{ + "label": "Seq Scan (ms)", + "data": [39, 37, 35, 40, 40], + "backgroundColor": "rgba(16, 185, 129, 0.6)", + "borderColor": "rgba(16, 185, 129, 1)", + "borderWidth": 1 + }, { + "label": "HashAggregate (ms)", + "data": [40, 86, 112, 120, 180], + "backgroundColor": "rgba(245, 158, 11, 0.6)", + "borderColor": "rgba(245, 158, 11, 1)", + "borderWidth": 1 + }] +}` options=`{ + "scales": { + "x": { "stacked": true }, + "y": { "stacked": true, "beginAtZero": true, "title": { "display": true, "text": "Time (ms)" } + } + }, + "plugins": { + "title": { "display": true, "text": "PostgreSQL Query Performance" } + } +}` >}} - `Seq Scan` is stable for all queries, which makes sense because the same data is required. - `HashAggregate` are different because of the choice of data processing @@ -191,14 +209,71 @@ I need to fetch the data and expose it in meaningful Python types. The expected This format may give a boost to `composite binary`, because the driver converts the binary in this exact format. Otherwise I need to manually convert the data. I use the `array` version of all `json` over `object`, because object are costlier the create and read. -| Test | total | postgres | python | -| -------------------- | ------ | -------- | ------ | -| `composite binary` | 220 ms | 80 ms | 140 ms | -| `json array text` | 230 ms | 120 ms | 110 ms | -| `json array binary` | 230 ms | 120 ms | 110 ms | -| `jsonb array binary` | 260 ms | 150 ms | 110 ms | -| `jsonb array text` | 270ms | 150 ms | 120 ms | -| `composite text` | 310 ms | 80 ms | 230 ms | +I use pytest and pytest-benchmark to write the benchmark. Here is a sample of the code I have to write, but the full file is available at the end. + +```py +def load_any_json_array_json( + conn: Connection, query: bytes, *, binary: bool +) -> JSONOut: + with conn.cursor() as cursor: + cursor.execute(query, binary=binary) + rows = cursor.fetchall() + + return [ + ( + row[0], + [{"date": item[0], "price": item[1]} for item in row[1]], + ) + for row in rows + ] + +#... + +@pytest.mark.benchmark(group="json out") +class TestJSONOut: + @pytest.mark.parametrize("binary", [False, True]) + @pytest.mark.parametrize( + "expr", + [JSON_OBJECT_EXPR, JSONB_OBJECT_EXPR], + ids=["json object", "jsonb object"], + ) + def test_json_object( + self, + conn: Connection, + benchmark: BenchmarkFixture, + binary: bool, + expr: str, + ): + benchmark( + load_any_json_object_json, conn, BASE_QUERY.format(expr), binary=binary + ) +``` + +{{< chart type="bar" data=`{ + "labels": ["composite binary", "json array text", "json array binary", "jsonb array binary", "jsonb array text", "composite text"], + "datasets": [{ + "label": "PostgreSQL (ms)", + "data": [80, 120, 120, 150, 150, 80], + "backgroundColor": "rgba(59, 130, 246, 0.6)", + "borderColor": "rgba(59, 130, 246, 1)", + "borderWidth": 1 + }, { + "label": "Python (ms)", + "data": [140, 110, 110, 110, 120, 230], + "backgroundColor": "rgba(245, 158, 11, 0.6)", + "borderColor": "rgba(245, 158, 11, 1)", + "borderWidth": 1 + }] +}` options=`{ + "scales": { + "x": { "stacked": true }, + "y": { "stacked": true, "beginAtZero": true, "title": { "display": true, "text": "Time (ms)" } } + }, + "plugins": { + "title": { "display": true, "text": "Python Processing Performance" } + } +}` >}} + - JSON parsing seems stable across all runs - Composite binary seems a little slower, but not by much - Composite text is much slower @@ -224,14 +299,32 @@ I have to fetch the data and format it as JSON. I'm not pushing it to the point This time, I use JSON objects, as this is the shape of the data transmitted. It should give a boost to all JSON queries, while composite still requires processing. -| Test | total | postgres | python | -| --------------------- | ------ | -------- | ------ | -| `json object binary` | 220 ms | 160 ms | 60 ms | -| `json object text` | 230 ms | 160 ms | 70 ms | -| `jsonb object binary` | 270 ms | 220 ms | 50 ms | -| `composite text` | 280 ms | 80 ms | 200 ms | -| `jsonb object text` | 280 ms | 220 ms | 60 ms | -| `composite binary` | 280 ms | 80 ms | 200 ms | +{{< chart type="bar" data=`{ + "labels": ["json object binary", "json object text", "jsonb object binary", "composite text", "jsonb object text", "composite binary"], + "datasets": [{ + "label": "PostgreSQL (ms)", + "data": [160, 160, 220, 80, 220, 80], + "backgroundColor": "rgba(59, 130, 246, 0.6)", + "borderColor": "rgba(59, 130, 246, 1)", + "borderWidth": 1 + }, { + "label": "Python (ms)", + "data": [60, 70, 50, 200, 60, 200], + "backgroundColor": "rgba(245, 158, 11, 0.6)", + "borderColor": "rgba(245, 158, 11, 1)", + "borderWidth": 1 + }] +}` options=`{ + "scales": { + "x": { "stacked": true }, + "y": { "stacked": true, "beginAtZero": true, "title": { "display": true, "text": "Time (ms)" } + } + }, + "plugins": { + "title": { "display": true, "text": "JSON API Performance" } + } +}` >}} + - All `json` processing look the same - `composite` in much slower in Python, regardless of binary or text @@ -242,9 +335,12 @@ All JSON outputs are ready for output, so they require the less work on the Pyth I don't really know why `composite text` is that slow in both benchmarks. ## Resources + - [Benchmarking script](test.py) +- [Postgres JSON functions](https://www.postgresql.org/docs/current/functions-json.html) +- [Postgres aggregation functions](https://www.postgresql.org/docs/current/functions-aggregate.html) +- [Psycopg](https://www.psycopg.org/) ## TODO -- [ ] Resources: postgres json, postgres aggregation, psycopg -- [ ] Charts > tables +- [ ] Real case study |