Thread

1. Performance Issue when using gin index

   谭忠涛 <zhongtao.tan@seaboxdata.com> — 2025-01-21T02:30:24Z

   The performance of creating a gin index before inserting data is different from that of inserting data after creating a gin index.
   Case:
   -- first make pg_trgm
   create extension pg_trgm;
   create table t1(a int, b varchar(20));
   create index t1_b on t1 using gin(b gin_trgm_ops);
   insert into t1 select a, a || substr('abcdefg', (random()*100000)::int%10000, 10) || a from generate_series(1,100000) t(a);
   analyze t1;
   explain analyze select * from t1 where b like '%abc%'; -- slow
   reindex index t1_b;
   explain analyze select * from t1 where b like '%abc%'; -- normal
   
   
   
   
   
   Regards
   
   
   
   谭忠涛   数据研究院数据库事业部
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2. Re: Performance Issue when using gin index

   Tom Lane <tgl@sss.pgh.pa.us> — 2025-01-21T03:01:40Z

   "=?utf-8?B?6LCt5b+g5rab?=" <zhongtao.tan@seaboxdata.com> writes:
   > The performance of creating a gin index before inserting data is different from that of inserting data after creating a gin index.
   
   This isn't terribly surprising.  Read
   
   https://www.postgresql.org/docs/current/gin.html#GIN-FAST-UPDATE
   
   There's also useful info in
   
   https://www.postgresql.org/docs/current/gin.html#GIN-TIPS
   
   			regards, tom lane