PostgreSQL 如何高效解决按任意字段分词检索的问题 - case 1

2022-03-04 08:37:07

背景

在有些应用场景中，可能会涉及多个字段的匹配。

例如这样的场景，一张表包含了几个字段，分别为歌手，曲目，专辑名称，作曲，歌词，。。。

用户可能要在所有的字段中以分词的方式匹配刘德华，任意字段匹配即返回TRUE。

传统的做法是每个字段建立分词索引，然后挨个匹配。

这样就导致SQL写法很冗长，而且要使用大量的OR操作。有没有更好的方法呢？

当然有，可以将整条记录输出为一个字符串，然后对这个字符串建立分词索引。

但是问题来了，整条记录输出的格式是怎么样的，会不会影响分词结果。

PostgreSQL 行记录的输出格式

create table t1(id int, c1 text, c2 text, c3 text);  
insert into t1 values (1 , '子远e5a1cbb8' , '子远e5a1cbb8' , 'abc');  

postgres=# select t1::text from t1;
                t1                 
-----------------------------------
 (1,子远e5a1cbb8,子远e5a1cbb8,abc)
(1 row)

postgres=# \df+ record_out
                                                                  List of functions
   Schema   |    Name    | Result data type | Argument data types |  Type  | Security | Volatility |  Owner   | Language | Source code | Description 
------------+------------+------------------+---------------------+--------+----------+------------+----------+----------+-------------+-------------
 pg_catalog | record_out | cstring          | record              | normal | invoker  | stable     | postgres | internal | record_out  | I/O
(1 row)

record类型输出对应的源码
src/backend/utils/adt/rowtypes.c

/*
 * record_out           - output routine for any composite type.
 */
Datum
record_out(PG_FUNCTION_ARGS)
{
...
        /* And build the result string */
        initStringInfo(&buf);

        appendStringInfoChar(&buf, '(');  // 首尾使用括弧

        for (i = 0; i < ncolumns; i++)
        {
...
                if (needComma)
                        appendStringInfoChar(&buf, ',');  // 字段间使用逗号
                needComma = true;
...
                /* Detect whether we need double quotes for this value */
                nq = (value[0] == '\0');        /* force quotes for empty string */
                for (tmp = value; *tmp; tmp++)
                {
                        char            ch = *tmp;

                        if (ch == '"' || ch == '\\' ||
                                ch == '(' || ch == ')' || ch == ',' ||
                                isspace((unsigned char) ch))
                        {
                                nq = true;
                                break;
                        }
                }

                /* And emit the string */
                if (nq)
                        appendStringInfoCharMacro(&buf, '"');  // 某些类型使用""号
                for (tmp = value; *tmp; tmp++)
                {
                        char            ch = *tmp;

                        if (ch == '"' || ch == '\\')
                                appendStringInfoCharMacro(&buf, ch);
                        appendStringInfoCharMacro(&buf, ch);
                }
                if (nq)
                        appendStringInfoCharMacro(&buf, '"');
        }

        appendStringInfoChar(&buf, ')');
...

scws分词的问题

看似不应该有问题，只是多个逗号，多了双引号，这些都是字符，scws分词应该能处理。
但是实际上有点问题，例子：
这两个词只是末尾不一样，多个个逗号就变这样了

postgres=# select * from ts_debug('scwscfg', '子远e5a1cbb8,');
 alias | description | token | dictionaries | dictionary | lexemes 
-------+-------------+-------+--------------+------------+---------
 k     | head        | 子    | {}           |            | 
 a     | adjective   | 远    | {simple}     | simple     | {远}
 e     | exclamation | e5a   | {simple}     | simple     | {e5a}
 e     | exclamation | 1cbb  | {simple}     | simple     | {1cbb}
 e     | exclamation | 8     | {simple}     | simple     | {8}
 u     | auxiliary   | ,     | {}           |            | 
(6 rows)

postgres=# select * from ts_debug('scwscfg', '子远e5a1cbb8');
 alias | description |  token   | dictionaries | dictionary |  lexemes   
-------+-------------+----------+--------------+------------+------------
 k     | head        | 子       | {}           |            | 
 a     | adjective   | 远       | {simple}     | simple     | {远}
 e     | exclamation | e5a1cbb8 | {simple}     | simple     | {e5a1cbb8}
(3 rows)

问题分析的手段

PostgreSQL分词的步骤简介

.1. 使用parse将字符串拆分成多个token，以及每个token对应的token type
所以创建text search configuration时，需要指定parser，parser也是分词的核心

Command:     CREATE TEXT SEARCH CONFIGURATION
Description: define a new text search configuration
Syntax:
CREATE TEXT SEARCH CONFIGURATION name (
    PARSER = parser_name |
    COPY = source_config
)

同时parser支持哪些token type也是建立parser时必须指定的

Command:     CREATE TEXT SEARCH PARSER
Description: define a new text search parser
Syntax:
CREATE TEXT SEARCH PARSER name (
    START = start_function ,
    GETTOKEN = gettoken_function ,
    END = end_function ,
    LEXTYPES = lextypes_function
    [, HEADLINE = headline_function ]
)

查看已创建了哪些parser

postgres=# select * from pg_ts_parser ;
 prsname | prsnamespace |   prsstart   |     prstoken     |   prsend   |  prsheadline  |   prslextype   
---------+--------------+--------------+------------------+------------+---------------+----------------
 default |           11 | prsd_start   | prsd_nexttoken   | prsd_end   | prsd_headline | prsd_lextype
 scws    |         2200 | pgscws_start | pgscws_getlexeme | pgscws_end | prsd_headline | pgscws_lextype
 jieba   |         2200 | jieba_start  | jieba_gettoken   | jieba_end  | prsd_headline | jieba_lextype
(3 rows)

查看parser支持的token type如下
scws中的释义
http://www.xunsearch.com/scws/docs.php#attr

postgres=# select * from ts_token_type('scws');
 tokid | alias |  description  
-------+-------+---------------
    97 | a     | adjective
    98 | b     | difference
    99 | c     | conjunction
   100 | d     | adverb
   101 | e     | exclamation
   102 | f     | position
   103 | g     | word root
   104 | h     | head
   105 | i     | idiom
   106 | j     | abbreviation
   107 | k     | head
   108 | l     | temp
   109 | m     | numeral
   110 | n     | noun
   111 | o     | onomatopoeia
   112 | p     | prepositional
   113 | q     | quantity
   114 | r     | pronoun
   115 | s     | space
   116 | t     | time
   117 | u     | auxiliary
   118 | v     | verb
   119 | w     | punctuation
   120 | x     | unknown
   121 | y     | modal
   122 | z     | status
(26 rows)

.2. 每种toke type，对应一个或多个字典进行匹配处理

ALTER TEXT SEARCH CONFIGURATION name
    ADD MAPPING FOR token_type [, ... ] WITH dictionary_name [, ... ]

查看已配置的token type 与 dict 的map信息

postgres=# select * from pg_ts_config_map ;

.3. 第一个适配token的字典，将token输出转换为lexeme

(会去除stop words)，去复数等。

以下几个函数可以用来调试分词的问题

ts_token_type(parser_name text, OUT tokid integer, OUT alias text, OUT description text)
返回指定parser 支持的token type
ts_parse(parser_name text, txt text, OUT tokid integer, OUT token text)
指定parser, 将字符串输出为token
ts_debug(config regconfig, document text, OUT alias text, OUT description text, OUT token text, OUT dictionaries regdictionary[], OUT dictionary regdictionary, OUT lexemes text[])
指定分词配置，将字符串输出为token以及额外的信息

上面的例子，我们可以看到使用scws parser时，输出的token发生了变化

postgres=# select * from pg_ts_parser ;
 prsname | prsnamespace |   prsstart   |     prstoken     |   prsend   |  prsheadline  |   prslextype   
---------+--------------+--------------+------------------+------------+---------------+----------------
 default |           11 | prsd_start   | prsd_nexttoken   | prsd_end   | prsd_headline | prsd_lextype
 scws    |         2200 | pgscws_start | pgscws_getlexeme | pgscws_end | prsd_headline | pgscws_lextype
 jieba   |         2200 | jieba_start  | jieba_gettoken   | jieba_end  | prsd_headline | jieba_lextype
(3 rows)

postgres=# select * from ts_parse('scws', '子远e5a1cbb8,');
 tokid | token 
-------+-------
   107 | 子
    97 | 远
   101 | e5a
   101 | 1cbb
   101 | 8
   117 | ,
(6 rows)

如何解决

在不修改scws代码的情况下，我们可以先将逗号替换为空格，scws是会忽略空格的

postgres=# select replace(t1::text, ',', ' ') from t1; 
              replace              
-----------------------------------
 (1 子远e5a1cbb8 子远e5a1cbb8 abc)
(1 row)

postgres=# select to_tsvector('scwscfg', replace(t1::text, ',', ' ')) from t1; 
              to_tsvector              
---------------------------------------
 '1':1 'abc':6 'e5a1cbb8':3,5 '远':2,4
(1 row)

行全文检索索引用法

postgres=# create or replace function rec_to_text(anyelement) returns text as 
$$

select $1::text;

$$
 language sql strict immutable;
CREATE FUNCTION

postgres=# create index idx on t1 using gin (to_tsvector('scwscfg', replace(rec_to_text(t1), ',', ' ')));
CREATE INDEX

SQL写法
postgres=# explain verbose select * from t1 where to_tsvector('scwscfg', replace(rec_to_text(t1), ',', ' ')) @@ to_tsquery('scwscfg', '子远e5a1cbb8');
                                                                  QUERY PLAN                                                                   
-----------------------------------------------------------------------------------------------------------------------------------------------
 Bitmap Heap Scan on public.t1  (cost=4.50..6.52 rows=1 width=100)
   Output: c1, c2, c3, c4
   Recheck Cond: (to_tsvector('scwscfg'::regconfig, replace(rec_to_text(t1.*), ','::text, ' '::text)) @@ '''远'' & ''e5a1cbb8'''::tsquery)
   ->  Bitmap Index Scan on idx  (cost=0.00..4.50 rows=1 width=0)
         Index Cond: (to_tsvector('scwscfg'::regconfig, replace(rec_to_text(t1.*), ','::text, ' '::text)) @@ '''远'' & ''e5a1cbb8'''::tsquery)
(5 rows)

参考

http://www.xunsearch.com/scws/docs.php#attr
https://github.com/jaiminpan/pg_jieba
https://github.com/jaiminpan/pg_scws
https://yq.aliyun.com/articles/7730
分词速度，每CPU核约4.44万字/s。

postgres=# create extension pg_scws;
CREATE EXTENSION
Time: 6.544 ms
postgres=# alter function to_tsvector(regconfig,text) volatile;
ALTER FUNCTION
postgres=# select to_tsvector('scwscfg','*万岁，如何加快PostgreSQL结巴分词加载速度');
                                       to_tsvector                                       
-----------------------------------------------------------------------------------------
 'postgresql':4 '万岁':2 '*':1 '分词':6 '加快':3 '加载':7 '结巴':5 '速度':8
(1 row)
Time: 0.855 ms
postgres=# set zhparser.dict_in_memory = t;
SET
Time: 0.339 ms
postgres=# explain (buffers,timing,costs,verbose,analyze) select to_tsvector('scwscfg','*万岁，如何加快PostgreSQL结巴分词加载速度') from generate_series(1,100000);
                                                               QUERY PLAN                                                               
------------------------------------------------------------------------------------------------------------
 Function Scan on pg_catalog.generate_series  (cost=0.00..260.00 rows=1000 width=0) (actual time=11.431..17971.197 rows=100000 loops=1)
   Output: to_tsvector('scwscfg'::regconfig, '*万岁，如何加快PostgreSQL结巴分词加载速度'::text)
   Function Call: generate_series(1, 100000)
   Buffers: temp read=172 written=171
 Planning time: 0.042 ms
 Execution time: 18000.344 ms
(6 rows)
Time: 18000.917 ms
postgres=# select 8*100000/18.000344;
      ?column?      
--------------------
 44443.595077960732
(1 row)

cpu

Architecture:          x86_64
CPU op-mode(s):        32-bit, 64-bit
Byte Order:            Little Endian
CPU(s):                32
On-line CPU(s) list:   0-31
Thread(s) per core:    1
Core(s) per socket:    32
Socket(s):             1
NUMA node(s):          1
Vendor ID:             GenuineIntel
CPU family:            6
Model:                 63
Model name:            Intel(R) Xeon(R) CPU E5-2680 v3 @ 2.50GHz
Stepping:              2
CPU MHz:               2494.224
BogoMIPS:              4988.44
Hypervisor vendor:     KVM
Virtualization type:   full
L1d cache:             32K
L1i cache:             32K
L2 cache:              256K
L3 cache:              30720K
NUMA node0 CPU(s):     0-31

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码农公寓

背景

PostgreSQL 行记录的输出格式

scws分词的问题

问题分析的手段

如何解决

行全文检索 索引用法

参考

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行全文检索索引用法