[pgpool-hackers: 3708] Re: Query mis cached

[Hou, Zhijie]

Hi Ishii san

> For DELETE and UPDATE statement, I think you need to cast
> cte->ctequery to DeleteStmt or UpdateStmt accordingly.

Thanks for reviewing the patch.
It's my fault, I forgot to check when copying the code.

I fixed the mistake and made a new patch.

Best regards,
houzj

-----Original Message-----
From: Tatsuo Ishii [mailto:ishii at sraoss.co.jp] 
Sent: Friday, July 10, 2020 9:49 AM
To: Hou, Zhijie/侯 志杰 <houzj.fnst at cn.fujitsu.com>
Cc: pgpool-hackers at pgpool.net
Subject: Re: [pgpool-hackers: 3706] Re: Query mis cached

>> I found the following SQL will be cached, when enabled memory query 
>> cache,
>> 
>> 
>> 
>>         "with cte as (insert into test2 values(1) returning *) select * from test2;"
>> 
>> 
>> 
>> I think the SQL has Data-Modifying Statements in with clause should not be cached.
>> 
>> Because Once cached, the Data-Modifying Statements will not be executed again which is not expected.
> 
> You are right.

At the time when query cache was implemented, there's no WITH + DML. That's why we missed that.

>> It seems to be better to analyze the with clause like the following:
>> 
>> 
>> 
>> --------For UPDATE/INSERT/DELETE type SQL:
>> 
>>                 extract oids from its with clause which will be invalidated.
>> 
>> 
>> 
>> --------For SELECT type SQL:
>> 
>>                 If Data-Modifying Statements in its with clause, the 
>> select will not be cached,
>> 
>>                 and the oids from with clause will be invalidated too.
>> 
>> 
>> 
>> What do you think?

Sounds like a correct idea.

>> 
>> 
>> I try to solve the problem and made a patch for the code.
> 
> Thank you for the patch! I will look into this.

In 0002-Update-pool_memqcache.c.patch:

+		else if(IsA(cte->ctequery, DeleteStmt))
+		{
+			InsertStmt *stmt = (InsertStmt *) cte->ctequery;
+			table = make_table_name_from_rangevar(stmt->relation);
+		}
+		else if(IsA(cte->ctequery, UpdateStmt))
+		{
+			InsertStmt *stmt = (InsertStmt *) cte->ctequery;
+			table = make_table_name_from_rangevar(stmt->relation);
+		}

For DELETE and UPDATE statement, I think you need to cast
cte->ctequery to DeleteStmt or UpdateStmt accordingly.

Best regards,
--
Tatsuo Ishii
SRA OSS, Inc. Japan
English: http://www.sraoss.co.jp/index_en.php
Japanese:http://www.sraoss.co.jp




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