背景
世界是确定的吗? 不
就好像我们拍照, 同一个相机, 同一个地点, 同一个时间连拍几张, 结果都不一样. 更不用说时间地点不一样了.
真正确定的数据并不多, 世界充满的是不确定的数据.
例如人脸识别, 存在数据库中的数据可能是曾经的照片, 但是你去比对人脸时是实时的, 角度、化妆、发型都可能不一样.
未来的数据库一定要解决一个问题, 如何在不确定的世界寻找确定的答案?
PolarDB早几年就发布了pase插件, 解决高性能图像识别的问题, 通过将非结构化数据根据特征提取成为一串向量, 然后根据向量进行距离计算, 得到最相似的向量, 从而解决不确定数据的确定性搜索.
后来开源社区也发了一个插件vector, 知识支持的算法只有ivfflat.
本文将介绍如何在开源polardb中安装和使用vector插件, 解决向量数据相似搜索的问题.
PolarDB的安装请参考: 《如何用 PolarDB 证明巴菲特的投资理念》
vector on PolarDB
启动并进入polardb实例
IT-C02YW2EFLVDL:~ digoal$ docker ps -a
CONTAINER ID IMAGE COMMAND CREATED STATUS PORTS NAMES
67e1eed1b4b6 polardb/polardb_pg_local_instance:htap "/bin/sh -c '~/tmp_b…" 2 months ago Exited (137) 10 minutes ago polardb_pg_htap
IT-C02YW2EFLVDL:~ digoal$ docker start 67e1eed1b4b6
67e1eed1b4b6
IT-C02YW2EFLVDL:~ digoal$ docker exec -it 67e1eed1b4b6 bash
[postgres@67e1eed1b4b6 ~]$ which git
/usr/bin/git 下载vector插件
[postgres@67e1eed1b4b6 ~]$ git clone --branch v0.3.2 --depth 1 https://github.com/pgvector/pgvector.git
Cloning into 'pgvector'...
remote: Enumerating objects: 80, done.
remote: Counting objects: 100% (80/80), done.
remote: Compressing objects: 100% (62/62), done.
remote: Total 80 (delta 33), reused 29 (delta 15), pack-reused 0
Unpacking objects: 100% (80/80), done.
Note: checking out 'a7f712b5a4724cfe55e2793dd1a4b7d48257fa1e'.
You are in 'detached HEAD' state. You can look around, make experimental
changes and commit them, and you can discard any commits you make in this
state without impacting any branches by performing another checkout.
If you want to create a new branch to retain commits you create, you may
do so (now or later) by using -b with the checkout command again. Example:
git checkout -b new_branch_name 安装vector插件
[postgres@67e1eed1b4b6 ~]$ cd pgvector/
[postgres@67e1eed1b4b6 pgvector]$ ll
total 48
-rw-rw-r-- 1 postgres postgres 1877 Dec 1 09:34 CHANGELOG.md
-rw-rw-r-- 1 postgres postgres 482 Dec 1 09:34 Dockerfile
-rw-rw-r-- 1 postgres postgres 1104 Dec 1 09:34 LICENSE
-rw-rw-r-- 1 postgres postgres 1760 Dec 1 09:34 Makefile
-rw-rw-r-- 1 postgres postgres 1105 Dec 1 09:34 META.json
-rw-rw-r-- 1 postgres postgres 9495 Dec 1 09:34 README.md
drwxrwxr-x 2 postgres postgres 4096 Dec 1 09:34 sql
drwxrwxr-x 2 postgres postgres 4096 Dec 1 09:34 src
drwxrwxr-x 6 postgres postgres 4096 Dec 1 09:34 test
-rw-rw-r-- 1 postgres postgres 135 Dec 1 09:34 vector.control
[postgres@67e1eed1b4b6 pgvector]$ which pg_config
~/tmp_basedir_polardb_pg_1100_bld/bin/pg_config
[postgres@67e1eed1b4b6 pgvector]$ USE_PGXS=1 make
[postgres@67e1eed1b4b6 pgvector]$ USE_PGXS=1 make install 加载vector插件
[postgres@67e1eed1b4b6 pgvector]$ psql -h 127.0.0.1
psql (11.9)
Type "help" for help.
postgres=# create extension vector ;
CREATE EXTENSION 测试向量数据搜索、以及索引加速搜索.
postgres=# CREATE TABLE items (embedding vector(3));
CREATE TABLE
postgres=# INSERT INTO items VALUES ('[1,2,3]'), ('[4,5,6]');
INSERT 0 2
postgres=# SELECT * FROM items ORDER BY embedding <-> '[3,1,2]' LIMIT 1;
embedding
-----------
[1,2,3]
(1 row)
postgres=# CREATE INDEX ON items USING ivfflat (embedding vector_l2_ops) WITH (lists = 100);
CREATE INDEX
postgres=# SELECT * FROM items ORDER BY embedding <-> '[3,1,2]' LIMIT 1;
embedding
-----------
[1,2,3]
(1 row)
postgres=# explain SELECT * FROM items ORDER BY embedding <-> '[3,1,2]' LIMIT 1;
QUERY PLAN
------------------------------------------------------------------
Limit (cost=1.03..1.04 rows=1 width=40)
-> Sort (cost=1.03..1.04 rows=2 width=40)
Sort Key: ((embedding <-> '[3,1,2]'::vector))
-> Seq Scan on items (cost=0.00..1.02 rows=2 width=40)
(4 rows)
postgres=# set enable_seqscan=off;
SET
postgres=# explain SELECT * FROM items ORDER BY embedding <-> '[3,1,2]' LIMIT 1;
QUERY PLAN
----------------------------------------------------------------------------------------
Limit (cost=4.08..6.09 rows=1 width=40)
-> Index Scan using items_embedding_idx on items (cost=4.08..8.11 rows=2 width=40)
Order By: (embedding <-> '[3,1,2]'::vector)
(3 rows)
postgres=# SET ivfflat.probes = 10;
SET
postgres=# SELECT * FROM items ORDER BY embedding <-> '[3,1,2]' LIMIT 1;
embedding
-----------
[1,2,3]
(1 row)
postgres=# explain SELECT * FROM items ORDER BY embedding <-> '[3,1,2]' LIMIT 1;
QUERY PLAN
------------------------------------------------------------------------------------------
Limit (cost=40.80..42.81 rows=1 width=40)
-> Index Scan using items_embedding_idx on items (cost=40.80..44.83 rows=2 width=40)
Order By: (embedding <-> '[3,1,2]'::vector)
(3 rows) 
