一、前提条件
实例为云数据库 PostgreSQL 10、11、12、13、14、15、16、17、18全新版本。
二、背景信息
Roaring Bitmap 算法是将32位的 INT 类型数据划分为216个数据块（Chunk），每一个数据块对应整数的高16位，并使用一个容器（Container）来存放一个数值的低16位。
Roaring Bitmap 将这些容器保存在一个动态数组中，作为一级索引。容器使用两种不同的结构：数组容器（Array Container）和位图容器（Bitmap Container）。数组容器存放稀疏的数据，位图容器存放稠密的数据。如果一个容器里面的整数数量小于4096，就用数组容器来存储值。若大于4096，就用位图容器来存储值。
采用这种存储结构，Roaring Bitmap 可以快速检索一个特定的值。在做位图计算（AND、OR、XOR）时，Roaring Bitmap 提供了相应的算法来高效地实现在两种容器之间的运算。使得 Roaring Bitmap 无论在存储和计算性能上都表现优秀。
三、操作步骤
1. 创建插件。示例如下：
CREATE EXTENSION roaringbitmap;
2. 创建带有 RoaringBitmap 数据类型的表。示例如下：
CREATE TABLE t1 (id integer, bitmap roaringbitmap);
3. 使用 rb_build 函数插入 roaringbitmap 的数据。示例如下：
–数组位置对应的 BIT 值为1INSERT INTO t1 SELECT 1,RB_BUILD(ARRAY[1,2,3,4,5,6,7,8,9,200]);–将输入的多条记录的值对应位置的 BIT 值设置为1，最后聚合为一个 roaringbitmap INSERT INTO t1 SELECT 2,RB_BUILD_AGG(e) FROM GENERATE_SERIES(1,100) e;
4. 进行 Bitmap 计算（OR、AND、XOR、ANDNOT）。示例如下：
–数组位置对应的 BIT 值为1SELECT RB_OR(a.bitmap,b.bitmap) FROM (SELECT bitmap FROM t1 WHERE id = 1) AS a,(SELECT bitmap FROM t1 WHERE id = 2) AS b;
5. 进行 Bitmap 聚合计算（OR、AND、XOR、BUILD），并生成新的 roaringbitmap 类型。示例如下：
SELECT RB_OR_AGG(bitmap) FROM t1;SELECT RB_AND_AGG(bitmap) FROM t1;SELECT RB_XOR_AGG(bitmap) FROM t1;SELECT RB_BUILD_AGG(e) FROM GENERATE_SERIES(1,100) e;
6. 统计基数（Cardinality），即统计 roaringbitmap 中包含多少个位置为1的 BIT 位。示例如下：
SELECT RB_CARDINALITY(bitmap) FROM t1;
7. 从 roaringbitmap 中返回位置为1的 BIT 下标（即位置值）。示例如下：
SELECT RB_ITERATE(bitmap) FROM t1 WHERE id = 1;
四、功能函数列表
| 函数名 | 输入 | 输出 | 描述 | 示例 | 结果 |
| rb_build | integer[] | roaringbitmap | Create roaringbitmap from integer array | “rb_build('{1,2,3,4,5}')“ | {1,2,3,4,5} |
| rb_index | roaringbitmap,integer | bigint | Return the 0-based index of element in this roaringbitmap, or -1 if do not exsits | “rb_index('{1,2,3}',3)“ | 2 |
| rb_cardinality | roaringbitmap | bigint | Return cardinality of the roaringbitmap | “rb_cardinality('{1,2,3,4,5}')“ | 5 |
| rb_and_cardinality | roaringbitmap,roaringbitmap | bigint | Return cardinality of the AND of two roaringbitmaps | “rb_or_cardinality('{1,2,3}','{3,4,5}')“ | 1 |
| rb_xor_cardinality | roaringbitmap,roaringbitmap | bigint | Return cardinality of the XOR of two roaringbitmaps | “rb_xor_cardinality('{1,2,3}','{3,4,5}')“ | 4 |
| rb_andnot_cardinality | roaringbitmap,roaringbitmap | bigint | Return cardinality of the ANDNOT of two roaringbitmaps | “rb_andnot_cardinality('{1,2,3}','{3,4,5}')“ | 2 |
| rb_is_empty | roaringbitmap | boolean | Check if roaringbitmap is empty. | “rb_is_empty('{1,2,3,4,5}')“ | t |
| rb_fill | roaringbitmap,range_start bigint,range_end bigint | roaringbitmap | Fill the specified range (not include the range_end) | “rb_fill('{1,2,3}',5,7)“ | {1,2,3,5,6} |
| rb_clear | roaringbitmap,range_start bigint,range_end bigint | roaringbitmap | Clear the specified range (not include the range_end) | “rb_clear('{1,2,3}',2,3)“ | {1,3} |
| rb_flip | roaringbitmap,range_start bigint,range_end bigint | roaringbitmap | Negative the specified range (not include the range_end) | “rb_flip('{1,2,3}',2,10)“ | {1,4,5,6,7,8,9} |
| rb_range | roaringbitmap,range_start bigint,range_end bigint | roaringbitmap | Return new set with specified range (not include the range_end) | “rb_range('{1,2,3}',2,3)“ | {2} |
| rb_range_cardinality | roaringbitmap,range_start bigint,range_end bigint | bigint | Return the cardinality of specified range (not include the range_end) | “rb_range_cardinality('{1,2,3}',2,3)“ | 1 |
| rb_min | roaringbitmap | integer | Return the smallest offset in roaringbitmap. Return NULL if the bitmap is empty | “rb_min('{1,2,3}')“ | 1 |
| rb_max | roaringbitmap | integer | Return the greatest offset in roaringbitmap. Return NULL if the bitmap is empty | “rb_max('{1,2,3}')“ | 3 |
| rb_rank | roaringbitmap,integer | bigint | Return the number of elements that are smaller or equal to the specified offset | “rb_rank('{1,2,3}',3)“ | 3 |
| rb_jaccard_dist | roaringbitmap,roaringbitmap | double precision | Return the jaccard distance(or the Jaccard similarity coefficient) of two bitmaps | “rb_jaccard_dist('{1,2,3}','{3,4}')“ | 0.25 |
| rb_select | roaringbitmap,bitset_limit bigint,bitset_offset bigint=0,reverse boolean=false,range_start bigint=0,range_end bigint=4294967296 | roaringbitmap | Return subset [bitset_offset,bitset_offset+bitset_limit) of bitmap between range [range_start,range_end) | “rb_select('{1,2,3,4,5,6,7,8,9}',5,2)“ | {3,4,5,6,7} |
| rb_to_array | roaringbitmap | integer[] | Convert roaringbitmap to integer array | “rb_to_array(roaringbitmap('{1,2,3}'))“ | {1,2,3} |
| rb_iterate | roaringbitmap | SET of integer | Return set of integer from a roaringbitmap data. | “SELECT rb_iterate(rb_build('{1,2,3}'))“ | 123 |
五、聚合函数列表
| 聚合函数名 | 输入 | 输出 | 描述 | 示例 | 结果 |
| rb_build_agg | integer | roaringbitmap | Build a roaringbitmap from a integer set | select rb_build_agg(id) from (values (1),(2),(3)) t(id) | {1,2,3} |
| rb_or_agg | roaringbitmap | roaringbitmap | AND Aggregate calculations from a roaringbitmap set | select rb_or_agg(bitmap) from (values (roaringbitmap('{1,2,3}')), (roaringbitmap('{2,3,4}')) ) t(bitmap) | {1,2,3,4} |
| rb_and_agg | roaringbitmap | roaringbitmap | AND Aggregate calculations from a roaringbitmap set | select rb_and_agg(bitmap) from (values (roaringbitmap('{1,2,3}')), (roaringbitmap('{2,3,4}')) ) t(bitmap) | {2,3} |
| rb_xor_agg | roaringbitmap | roaringbitmap | XOR Aggregate calculations from a roaringbitmap set | select rb_xor_agg(bitmap) from (values (roaringbitmap('{1,2,3}')), (roaringbitmap('{2,3,4}')) ) t(bitmap) | {1,4} |
| rb_or_cardinality_agg | roaringbitmap | bigint | OR Aggregate calculations from a roaringbitmap set, return cardinality. | select rb_or_cardinality_agg(bitmap) from (values (roaringbitmap('{1,2,3}')), (roaringbitmap('{2,3,4}')) ) t(bitmap) | 4 |
| rb_and_cardinality_agg | roaringbitmap | bigint | AND Aggregate calculations from a roaringbitmap set, return cardinality | select rb_and_cardinality_agg(bitmap) from (values (roaringbitmap('{1,2,3}')), (roaringbitmap('{2,3,4}')) ) t(bitmap) | 2 |
| rb_xor_cardinality_agg | roaringbitmap | bigint | XOR Aggregate calculations from a roaringbitmap set, return cardinality | select rb_xor_cardinality_agg(bitmap) from (values (roaringbitmap('{1,2,3}')), (roaringbitmap('{2,3,4}')) ) t(bitmap) | 2 |