Better way of copying data? - mysql

I have two tables where I want to copy the post_id from one table to another when the testpostmeta.meta_value = testTable.stockcode
There's about 2000 rows in testTable and 65k rows in testpostmeta.
The code works, it just takes about 1-2 minutes to complete. Is there anything that can be done to speed the hamster wheel up?
UPDATE testTable
INNER JOIN testpostmeta
ON testTable.stockcode = testpostmeta.meta_value
SET testTable.post_id = testpostmeta.post_id
I tried adding WHERE testpostmeta.meta_value = testTable.stockcode but that didn't work.

be sure you have proper indexes on testTable and testpostmeta
CREATE INDEX my_idx1 ON testTable (stokcode);
CREATE INDEX my_idx2 ON testpostmeta (meta_value , post_id);

Try adding an index to each table that matches the field used for your JOIN criteria:
ALTER TABLE testTable ADD INDEX stockcode_idx(stockcode);
ALTER TABLE testpostmeta ADD INDEX meta_idx(meta_value);

You can stop the autocommit
SET autocommit = 0 ;
--Insert/Update/Delete stuff here
COMMIT ;

If post_id is indexed in target table that also can slow down the update.
Try disabling index before the operation and enable it after. So you data will be indexed once rather on each subsequent data change.
ALTER TABLE targetTable DISABLE KEYS;
-- Your UPDATE query
ALTER TABLE targetTable ENABLE KEYS;
And as said in the reference:
Performing multiple updates together is much quicker than doing one at a time if you lock the table.
Here some reference page that can give more idea on what can be done:
8.2.4.2 Optimizing UPDATE Statements
8.5.4 Bulk Data Loading for InnoDB Tables

Related

Mysql delete and optimize very slow

I searched Internet and Stack Overflow for my trouble, but couldn't find a good solution.
I have a table (MySql MyISAM) containing 300,000 rows (one column is blob field).
I must use:
DELETE FROM tablename WHERE id IN (1,4,7,88,568,.......)
There are nearly 30,000 id's in the IN syntax.
It takes nearly 1 hour. Also It does not make the .MYD file smaller although I delete 10% of it, so I run OPTIMIZE TABLE... command. It also lasts long...(I should use it, because disk space matters for me).
What's a way to improve performance when deleting the data as above and recover space? (Increasing buffer size? which one? or else?)
With IN, MySQL will scan all the rows in the table and match the record against the IN clause. The list of IN predicates will be sorted, and all 300,000 rows in the database will get a binary search against 30,000 ids.
If you do this with JOIN on a temporary table (no indexes on a temp table), assuming id is indexed, the database will do 30,000 binary lookups on a 300,000 record index.
So, 300,000 binary searches against 30,000 records, or 30,000 binary searches against 300,000 records... which is faster? The second one is faster, by far.
Also, delaying the index rebuilding with DELETE QUICK will result in much faster deletes. All records will simply be marked deleted, both in the data file and in the index, and the index will not be rebuilt.
Then, to recover space and rebuild the indexes at a later time, run OPTIMIZE TABLE.
The size of the list in your IN() statement may be the cause. You could add the IDs to a temporary table and join to do the deletes. Also, as you are using MyISAM you can use the DELETE QUICK option to avoid the index hit whilst deleting:
For MyISAM tables, if you use the QUICK keyword, the storage engine
does not merge index leaves during delete, which may speed up some
kinds of delete operations.
I think the best approach to make it faster is to create a new table and insert into it the rows which you dont want to delete and then drop the original table and then you can copy the content from the table to the main table.
Something like this:
INSERT INTO NewTable SELECT * FROM My_Table WHERE ... ;
Then you can use RENAME TABLE to rename the copy to the original name
RENAME TABLE My_Table TO My_Table_old, NewTable TO My_Table ;
And then finally drop the original table
DROP TABLE My_Table_old;
try this
create a table name temptable with a single column id
insert into table 1,4,7,88,568,......
use delete join something like
DELETE ab, b FROM originaltable AS a INNER JOIN temptable AS b ON a.id= b.id where b.id is null;
its just an idea . the query is not tested . you can check the syntax on google.

Taking forever to update a table from another

I have temp table with 14k records and main table with 5 million records, I am updating main table from temp table using below SQL
UPDATE customPricing t1
INNER JOIN customPricingIncremental t2 ON (t1.customerClass=t2.customerClass and t1.customerName=t2.customerName and t1.svcType=t2.svcType and t1.svcDuration=t2.svcDuration and t1.durationPeriod=t2.durationPeriod and t1.partNumberSKU=t2.partNumberSKU)
SET t1.customerId= t2.customerId, t1.customerNumber= t2.customerNumber, t1.custPartNumber=t2.custPartNumber, t1.sppl= t2.sppl ,t1.priceMSRP= t2.priceMSRP, t1.partnerPriceDistiDvarOEM= t2.partnerPriceDistiDvarOEM, t1.msrpSvcPrice=t2.msrpSvcPrice, t1.partnerSvcPrice=t2.partnerSvcPrice, t1.msrpBundlePrice=t2.msrpBundlePrice, t1.partnerBundlePrice=t2.partnerBundlePrice, t1.startDate=t2.startDate, t1.endDate=t2.endDate, t1.currency=t2.currency, t1.countryCode=t2.countryCode, t1.inventoryItemId=t2.inventoryItemId, t1.flexField1=t2.flexField1, t1.flexField2=t2.flexField2, t1.flexField3=t2.flexField3, t1.flexField4=t2.flexField4, t1.flexField5=t2.flexField5
CustomerClass, customerName, durationPeriod, svcDuration & partNumberSKU all are indexes on both tables with length of 10 only, there is no primary key/unique indexes for both.
It takes forever to update the table, and I get timedout in the end.
What I am doing wrong ?
Nitesh
Try to disable nonunique keys temporarily:
ALTER TABLE customPricing DISABLE KEYS
Now run your query, and then enable them again:
ALTER TABLE customPricing ENABLE KEYS
Do this from the mysql client or a script instead of phpmyadmin as the queries might only apply to the current session.
Also, watch out for any triggers in the target table.
Read more about

Optimize mySql for faster alter table add column

I have a table that has 170,002,225 rows with about 35 columns and two indexes. I want to add a column. The alter table command took about 10 hours. Neither the processor seemed busy during that time nor were there excessive IO waits. This is on a 4 way high performance box with tons of memory.
Is this the best I can do? Is there something I can look at to optimize the add column in tuning of the db?
I faced a very similar situation in the past and i improve the performance of the operation in this way :
Create a new table (using the structure of the current table) with the new column(s) included.
execute a INSERT INTO new_table (column1,..columnN) SELECT (column1,..columnN) FROM current_table;
rename the current table
rename the new table using the name of the current table.
ALTER TABLE in MySQL is actually going to create a new table with new schema, then re-INSERT all the data and delete the old table. You might save some time by creating the new table, loading the data and then renaming the table.
From "High Performance MySQL book" (the percona guys):
The usual trick for loading MyISAM table efficiently is to disable keys, load the data and renalbe the keys:
mysql> ALTER TABLE test.load_data DISABLE KEYS;
-- load data
mysql> ALTER TABLE test.load_data ENABLE KEYS;
Well, I would recommend using latest Percona MySQL builds plus since there is the following note in MySQL manual
In other cases, MySQL creates a
temporary table, even if the data
wouldn't strictly need to be copied.
For MyISAM tables, you can speed up
the index re-creation operation (which
is the slowest part of the alteration
process) by setting the
myisam_sort_buffer_size system
variable to a high value.
You can do ALTER TABLE DISABLE KEYS first, then add column and then ALTER TABLE ENABLE KEYS. I don't see anything can be done here.
BTW, can't you go MongoDB? It doesn't rebuild anything when you add column.
Maybe you can remove the index before alter the table because what is take most of the time to build is the index?
Combining some of the comments on the other answers, this was the solution that worked for me (MySQL 5.6):
create table mytablenew like mytable;
alter table mytablenew add column col4a varchar(12) not null after col4;
alter table mytablenew drop index index1, drop index index2,...drop index indexN;
insert into mytablenew (col1,col2,...colN) select col1,col2,...colN from mytable;
alter table mytablenew add index index1 (col1), add index index2 (col2),...add index indexN (colN);
rename table mytable to mytableold, mytablenew to mytable
On a 75M row table, dropping the indexes before the insert caused the query to complete in 24 minutes rather than 43 minutes.
Other answers/comments have insert into mytablenew (col1) select (col1) from mytable, but this results in ERROR 1241 (21000): Operand should contain 1 column(s) if you have the parenthesis in the select query.
Other answers/comments have insert into mytablenew select * from mytable;, but this results in ERROR 1136 (21S01): Column count doesn't match value count at row 1 if you've already added a column.

Delete, Truncate or Drop to clean out a table in MySQL

I am attempting to clean out a table but not get rid of the actual structure of the table. I have an id column that is auto-incrementing; I don't need to keep the ID number, but I do need it to keep its auto-incrementing characteristic. I've found delete and truncate but I'm worried one of these will completely drop the entire table rendering future insert commands useless.
How do I remove all of the records from the table so that I can insert new data?
drop table will remove the entire table with data
delete * from table will remove the data, leaving the autoincrement values alone. it also takes a while if there's a lot of data in the table.
truncate table will remove the data, reset the autoincrement values (but leave them as autoincrement columns, so it'll just start at 1 and go up from there again), and is very quick.
TRUNCATE will reset your auto-increment seed (on InnoDB tables, at least), although you could note its value before truncating and re-set accordingly afterwards using alter table:
ALTER TABLE t2 AUTO_INCREMENT = value
Drop will do just that....drop the table in question, unless the table is a parent to another table.
Delete will remove all the data that meets the condition; if no condition is specified, it'll remove all the data in the table.
Truncate is similar to delete; however, it resets the auto_increment counter back to 1 (or the initial starting value). However, it's better to use truncate over delete because delete removes the data by each row, thus having a performance hit than truncate. However, truncate will not work on InnoDB tables where referential integrity is enforced unless it is turned off before the truncate command is issued.
So, relax; unless you issue a drop command on the table, it won't be dropped.
Truncate table is what you are looking for
http://www.1keydata.com/sql/sqltruncate.html
Another possibility involves creating an empty copy of the table, setting the AUTO_INCREMENT (with some eventual leeway for insertions during the non-atomic operation) and then rotating both :
CREATE TABLE t2_new LIKE t2;
SELECT #newautoinc:=auto_increment /*+[leeway]*/
FROM information_schema.tables
WHERE table_name='t2';
SET #query = CONCAT("ALTER TABLE t2_new AUTO_INCREMENT = ", #newautoinc);
PREPARE stmt FROM #query;
EXECUTE stmt;
DEALLOCATE PREPARE stmt;
RENAME TABLE t2 TO t2_old, t2_new TO t2;
And then, you have the extra advantage of being still able to change your mind before removing the old table.
If you reconsider your decision, you can still bring back old records from the table before the operation:
INSERT /*IGNORE*/ INTO t2 SELECT * FROM t2_old /*WHERE [condition]*/;
When you're good you can drop the old table:
DROP TABLE t2_old;
I've just come across a situation where DELETE is drastically affecting SELECT performance compared to TRUNCATE on a full-text InnoDB query.
If I DELETE all rows and then repopulate the table (1million rows), a typical query takes 1s to come back.
If instead I TRUNCATE the table, and repopulate it in exactly the same way, a typical query takes 0.05s to come back.
YMMV, but for whatever reason for me on MariaDB 10.3.15-MariaDB-log DELETE seems to be ruining my index.

Quickest way to delete enormous MySQL table

I have an enormous MySQL (InnoDB) database with millions of rows in the sessions table that were created by an unrelated, malfunctioning crawler running on the same server as ours. Unfortunately, I have to fix the mess now.
If I try to truncate table sessions; it seems to take an inordinately long time (upwards of 30 minutes). I don't care about the data; I just want to have the table wiped out as quickly as possible. Is there a quicker way, or will I have to just stick it out overnight?
(As this turned up high in Google's results, I thought a little more instruction might be handy.)
MySQL has a convenient way to create empty tables like existing tables, and an atomic table rename command. Together, this is a fast way to clear out data:
CREATE TABLE new_foo LIKE foo;
RENAME TABLE foo TO old_foo, new_foo TO foo;
DROP TABLE old_foo;
Done
The quickest way is to use DROP TABLE to drop the table completely and recreate it using the same definition. If you have no foreign key constraints on the table then you should do that.
If you're using MySQL version greater than 5.0.3, this will happen automatically with a TRUNCATE. You might get some useful information out of the manual as well, it describes how a TRUNCATE works with FK constraints. http://dev.mysql.com/doc/refman/5.0/en/truncate-table.html
EDIT: TRUNCATE is not the same as a drop or a DELETE FROM. For those that are confused about the differences, please check the manual link above. TRUNCATE will act the same as a drop if it can (if there are no FK's), otherwise it acts like a DELETE FROM with no where clause.
EDIT: If you have a large table, your MariaDB/MySQL is running with a binlog_format as ROW and you execute a DELETE without a predicate/WHERE clause, you are going to have issues to keep up the replication or even, to keep your Galera nodes running without hitting a flow control state. Also, binary logs can get your disk full. Be careful.
The best way I have found of doing this with MySQL is:
DELETE from table_name LIMIT 1000;
Or 10,000 (depending on how fast it happens).
Put that in a loop until all the rows are deleted.
Please do try this as it will actually work. It will take some time, but it will work.
Couldn't you grab the schema drop the table and recreate it?
drop table should be the fastest way to get rid of it.
Have you tried to use "drop"? I've used it on tables over 20GB and it always completes in seconds.
If you just want to get rid of the table altogether, why not simply drop it?
Truncate is fast, usually on the order of seconds or less. If it took 30 minutes, you probably had a case of some foreign keys referencing the table you were truncating. There may also be locking issues involved.
Truncate is effectively as efficient as one can empty a table, but you may have to remove the foreign key references unless you want those tables scrubbed as well.
We had these issues. We no longer use the database as a session store with Rails 2.x and the cookie store. However, dropping the table is a decent solution. You may want to consider stopping the mysql service, temporarily disable logging, start things up in safe mode and then do your drop/create. When done, turn on your logging again.
I'm not sure why it's taking so long. But perhaps try a rename, and recreate a blank table. Then you can drop the "extra" table without worrying how long it takes.
searlea's answer is nice, but as stated in the comments, you lose the foreign keys during the fight.
this solution is similar: the truncate is executed within a second, but you keep the foreign keys.
The trick is that we disable/enable the FK checks.
SET FOREIGN_KEY_CHECKS=0;
CREATE TABLE NewFoo LIKE Foo;
insert into NewFoo SELECT * from Foo where What_You_Want_To_Keep
truncate table Foo;
insert into Foo SELECT * from NewFoo;
SET FOREIGN_KEY_CHECKS=1;
Extended answer - Delete all but some rows
My problem was: Because of a crazy script, my table was for with 7.000.000 junk rows. I needed to delete 99% of data in this table, this is why i needed to copy What I Want To Keep in a tmp table before deleteting.
These Foo Rows i needed to keep were depending on other tables, that have foreign keys, and indexes.
something like that:
insert into NewFoo SELECT * from Foo where ID in (
SELECT distinct FooID from TableA
union SELECT distinct FooID from TableB
union SELECT distinct FooID from TableC
)
but this query was always timing out after 1 hour.
So i had to do it like this:
CREATE TEMPORARY TABLE tmpFooIDS ENGINE=MEMORY AS (SELECT distinct FooID from TableA);
insert into tmpFooIDS SELECT distinct FooID from TableB
insert into tmpFooIDS SELECT distinct FooID from TableC
insert into NewFoo SELECT * from Foo where ID in (select ID from tmpFooIDS);
I theory, because indexes are setup correctly, i think both ways of populating NewFoo should have been the same, but practicaly it didn't.
This is why in some cases, you could do like this:
SET FOREIGN_KEY_CHECKS=0;
CREATE TABLE NewFoo LIKE Foo;
-- Alternative way of keeping some data.
CREATE TEMPORARY TABLE tmpFooIDS ENGINE=MEMORY AS (SELECT * from Foo where What_You_Want_To_Keep);
insert into tmpFooIDS SELECT ID from Foo left join Bar where OtherStuff_You_Want_To_Keep_Using_Bar
insert into NewFoo SELECT * from Foo where ID in (select ID from tmpFooIDS);
truncate table Foo;
insert into Foo SELECT * from NewFoo;
SET FOREIGN_KEY_CHECKS=1;