Database correction Script Performance optimization Two: Remove unnecessary queries and BULK INSERT SQL

Source: Internet
Author: User
Tags bulk insert

recently in a long database merge script, you want to merge table data from multiple sub-databases into one primary database. Here are the mistakes I made when I wrote the data correction script.

Unnecessary queries

Take a look at the following statement:

 regiondb =   db. Houyiregiondb () houyidb  =  db. HOUYIDB (Read_only=  =   Regiondb.query (vmmacsfromregiondbsql) houyidbret  =   Houyidb.query (vmmacsfromhouyidbsql)  if  len  (Regiondbret) ==  0  :  return  

        Houyidb.query (vmmacsfromhouyidbsql) to become an unnecessary query. If this query pulls a lot of data, it can be a waste of time. BYTE is Money! Today's programmers may not be as "stingy" as the previous programmers, but also "budget-conscious". The fix is simple, and the order of the statements is reversed:

= db. Houyiregiondb ()    =  regiondb.query (vmmacsfromregiondbsql)    iflen == 0 :        regiondb. Close ()        return    = db. HOUYIDB (read_only=False)    = houyidb.query (vmmacsfromhouyidbsql)

Lesson: Write a program to avoid thinking without hesitation.

Lock Timeout

    is checked because   insert x table while concurrent delete from X where .... Insert precedes, delete X statement waits for lock. Since insert X inserts a hundred thousand of records, it takes more than 1 minutes, while innodb_lock_wait_timeout = 50s (show variables like "%timeout%";)       
Here you need to optimize the SQL statement. The optimization method is to divide a hundred thousand of records into multiple commits, committing 1000 insert statements at a time. The code is as follows:
defDivideintogroups (Alltuples, numpergroup=1000):    " "divide tuples into group of tuples; Each group have no more than Numpergroup tuples default value of Numpergroup is" "groups=[] Totalnum=Len (alltuples)ifTotalnum <=numPerGroup:groups.append (alltuples)returngroups Start=0 Eachend= Start +Numpergroup whileStart <totalNum:groups.append (Alltuples[start:eachend]) Start+=Numpergroup eachend= Start +NumpergroupifEachend >=Totalnum:eachend=TotalnumreturngroupsdefInsertmanymany (Insertsql, Alltuples, db):" "insert many many records, usually more than 10000 insert once and insert (len/1000+1) times " "groups=divideintogroups (alltuples) Count=0 forGrouptuplesinchgroups:affectrows=Db.executemany (Insertsql, Grouptuples)ifAffectrows:count+=affectrows db.commit () needinsertnum=Len (alltuples) ispassedmsg= ('OK' ifNeedinsertnum==countElse 'SOME ERROR') Printandlog ("need insert%d records, and actual%d.%s"% (Needinsertnum, Count, ispassedmsg))

The calling method is as follows:

Insertsql = "INSERT into student (name, age) value (%s,%s)"

Alltuples = [("Zhang", +), ("Qian", +), ("Wang", "Max"), ..., ("Liu", 26)]

Insertmanymany (Insertsql, alltuples, DB)

    The effect is obvious. Originally inserted 32,000 records need 18s, now only need 2-3s,  originally inserted 129,968 Records need 67s, now only need 12-15s. At the same time, the insertion transaction for each commit is shortened, which reduces the lock wait time.

Database correction Script Performance optimization Two: Remove unnecessary queries and BULK INSERT SQL

Contact Us

The content source of this page is from Internet, which doesn't represent Alibaba Cloud's opinion; products and services mentioned on that page don't have any relationship with Alibaba Cloud. If the content of the page makes you feel confusing, please write us an email, we will handle the problem within 5 days after receiving your email.

If you find any instances of plagiarism from the community, please send an email to: and provide relevant evidence. A staff member will contact you within 5 working days.

A Free Trial That Lets You Build Big!

Start building with 50+ products and up to 12 months usage for Elastic Compute Service

  • Sales Support

    1 on 1 presale consultation

  • After-Sales Support

    24/7 Technical Support 6 Free Tickets per Quarter Faster Response

  • Alibaba Cloud offers highly flexible support services tailored to meet your exact needs.