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opt: use histograms for inverted JSON/ARRAY scan statistics
Fixes cockroachdb#56870 Release note (performance improvement): The optimizer now uses collected histograms statistics to better estimate the cost of JSON and ARRAY inverted index scans, which may lead to more efficient query plans.
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,130 @@ | ||
| exec-ddl | ||
| CREATE TABLE t ( | ||
| k INT PRIMARY KEY, | ||
| a INT[], | ||
| INVERTED INDEX a_idx (a) | ||
| ) | ||
| ---- | ||
|
|
||
| # Histogram boundaries are for JSON values `{}`, `{1}`, `{2}`, `{3}`. The | ||
| # row_count is lower than the sum of the histogram buckets num_eq's because some | ||
| # rows can have multiple inverted index entries, for example `{1, 2}`. There | ||
| # are: | ||
| # | ||
| # - 1000 rows total | ||
| # - 10 empty arrays | ||
| # - 990 arrays encoded into 1010 index entries | ||
| # | ||
| exec-ddl | ||
| ALTER TABLE t INJECT STATISTICS '[ | ||
| { | ||
| "columns": ["a"], | ||
| "created_at": "2018-01-01 1:00:00.00000+00:00", | ||
| "row_count": 1000, | ||
| "distinct_count": 3, | ||
| "null_count": 0, | ||
| "histo_col_type": "BYTES", | ||
| "histo_buckets": [ | ||
| { | ||
| "distinct_range": 0, | ||
| "num_eq": 10, | ||
| "num_range": 0, | ||
| "upper_bound": "\\x43" | ||
| }, | ||
| { | ||
| "distinct_range": 0, | ||
| "num_eq": 990, | ||
| "num_range": 0, | ||
| "upper_bound": "\\x89" | ||
| }, | ||
| { | ||
| "distinct_range": 0, | ||
| "num_eq": 10, | ||
| "num_range": 0, | ||
| "upper_bound": "\\x8a" | ||
| }, | ||
| { | ||
| "distinct_range": 0, | ||
| "num_eq": 10, | ||
| "num_range": 0, | ||
| "upper_bound": "\\x8b" | ||
| } | ||
| ] | ||
| } | ||
| ]' | ||
| ---- | ||
|
|
||
| # Containment of an empty array requires a scan over all array entries. | ||
| opt | ||
| SELECT * FROM t@a_idx WHERE a @> '{}' | ||
| ---- | ||
| index-join t | ||
| ├── columns: k:1(int!null) a:2(int[]!null) | ||
| ├── immutable | ||
| ├── stats: [rows=333.333333] | ||
| ├── key: (1) | ||
| ├── fd: (1)-->(2) | ||
| └── inverted-filter | ||
| ├── columns: k:1(int!null) | ||
| ├── inverted expression: /4 | ||
| │ ├── tight: true, unique: false | ||
| │ └── union spans: ["", ""] | ||
| ├── stats: [rows=1020] | ||
| ├── key: (1) | ||
| └── scan t@a_idx | ||
| ├── columns: k:1(int!null) a_inverted_key:4(int[]!null) | ||
| ├── inverted constraint: /4/1 | ||
| │ └── spans: ["", ""] | ||
| ├── flags: force-index=a_idx | ||
| ├── stats: [rows=1020, distinct(1)=1000, null(1)=0, distinct(4)=4, null(4)=0] | ||
| │ histogram(4)= 0 10 0 990 0 10 0 10 | ||
| │ <--- '\x43' --- '\x89' --- '\x8a' --- '\x8b' | ||
| ├── key: (1) | ||
| └── fd: (1)-->(4) | ||
|
|
||
| # An inverted index scan is preferred for a more selective filter. | ||
| opt | ||
| SELECT * FROM t WHERE a @> '{2}' | ||
| ---- | ||
| index-join t | ||
| ├── columns: k:1(int!null) a:2(int[]!null) | ||
| ├── immutable | ||
| ├── stats: [rows=111.111111] | ||
| ├── key: (1) | ||
| ├── fd: (1)-->(2) | ||
| └── scan t@a_idx | ||
| ├── columns: k:1(int!null) | ||
| ├── inverted constraint: /4/1 | ||
| │ └── spans: ["\x8a", "\x8a"] | ||
| ├── stats: [rows=10, distinct(4)=1, null(4)=0] | ||
| │ histogram(4)= 0 10 0 0 | ||
| │ <--- '\x8a' --- '\x8b' | ||
| └── key: (1) | ||
|
|
||
| # A disjunction requires scanning all entries that match either the left or the | ||
| # right. | ||
| opt | ||
| SELECT * FROM t WHERE a @> '{2}' OR a @> '{3}' | ||
| ---- | ||
| index-join t | ||
| ├── columns: k:1(int!null) a:2(int[]!null) | ||
| ├── immutable | ||
| ├── stats: [rows=333.333333, distinct(2)=3, null(2)=0] | ||
| ├── key: (1) | ||
| ├── fd: (1)-->(2) | ||
| └── inverted-filter | ||
| ├── columns: k:1(int!null) | ||
| ├── inverted expression: /4 | ||
| │ ├── tight: true, unique: false | ||
| │ └── union spans: ["\x8a", "\x8c") | ||
| ├── stats: [rows=20] | ||
| ├── key: (1) | ||
| └── scan t@a_idx | ||
| ├── columns: k:1(int!null) a_inverted_key:4(int[]!null) | ||
| ├── inverted constraint: /4/1 | ||
| │ └── spans: ["\x8a", "\x8c") | ||
| ├── stats: [rows=20, distinct(1)=19.6078431, null(1)=0, distinct(4)=2, null(4)=0] | ||
| │ histogram(4)= 0 10 0 10 | ||
| │ <--- '\x8a' --- '\x8b' | ||
| ├── key: (1) | ||
| └── fd: (1)-->(4) |
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