Re: Speeding up a pretty simple correlated update query
Hello All, I'm reposting this since I didn't get much response the last time, so I'm hoping to reach out again. My correlated update query (see below) was running for 9 days before I killed it. Here is my original question: I have a legacy application which was written using a compound primary key of an item number (non unique) along with a category ID. The combination of the item number and category ID make the records unique. I am in the process of replacing the compound (VARCHAR) keys with an unique integer key in these tables. So I have created an item_seq table and assigned a unique sequence number to each compound key -- it looks like this (all tables are myisam tables, and mysql version 5.0) desc item_seq; +---+--+--+-+-++ | Field | Type | Null | Key | Default | Extra | +---+--+--+-+-++ | seq | int(10) unsigned | NO | PRI | NULL| auto_increment | | itemid| char(11) | NO | MUL | || | category | char(4) | NO | | || +---+--+--+-+-++ I also have my main transactional table with about 180,000,000 rows -- it looks like this: desc item_trans; +-+---+--+-+-+---+ | Field | Type | Null | Key | Default | Extra | +-+---+--+-+-+---+ | seq | int(10) unsigned | NO | MUL | | | | itemid | char(11) | NO | PRI | | | | category| char(4) | NO | PRI | | | | transid | int(10) | NO | PRI | | | Currently the seq field is null for the entire table. So of course, I want to update the main transaction table with the new sequence number. So I've disabled all the keys on the item_trans table -- since I am updating every row, it wouldn't (shouldn't) be using the index anyway. Here is my correlated update query: update item_trans i, item_seq is set i.seq=is.seq where is.itemid=i.itemid and is.category=i.category; If I run an explain on the select version of the update, this is what I get: ++-+--++---++-++---+---+ | id | select_type | table| type | possible_keys | key| key_len | ref| rows | Extra | ++-+--++---++-++---+---+ | 1 | SIMPLE | item_trans| ALL| PRIMARY | NULL | NULL | NULL | 178948797 | | | 1 | SIMPLE | item_seq | eq_ref | itemid| itemid | 20 | g.item_trans.itemid,g.item_trans.category| 1 | | ++-+--++---++-++---+---+ ... which is exactly what I would expect it to do. Update every record of the item_trans table, and do a full index lookup on the items_seq table. SO... I've been running this query to update item_trans, and it's been running for 5 days now. I've also tried running this with the primary key index on the item_trans table (but not the seq index), and that ran slower in my initial tests. Are there any faster ways to update 180 million records with a correlated update query? And I'm fairly certain that trying to do this in PHP one-record at a time would take much longer than a SQL solution. Thanks, -Hank
Re: Speeding up a pretty simple correlated update query
So I've disabled all the keys on the item_trans table -- since I am updating every row, it wouldn't (shouldn't) be using the index anyway. You can't disable unique indexes or primary keys. They are always active. You can only deactivate non-unique indexes. Here are a couple of suggestions. For now drop the index on item_seq.seq and desc.seq. Are you sure you have a compound index on item_seq.itemid and item_seq.category?? do a Show create table item_seq and also Show create table desc to see what you've got. Make sure your my.cnf file has key_buffer_size=500M equal to about 30% of your available memory. You can always reduce it later. Of course there is another way of doing it, if you are willing to have the tail wag the dog. You may kick yourself for not discovering it yourself. :) set @num:=0; set @last:=''; create table new_item_trans select IF(concat(itemid,category),@last, @num:=...@num+1,@num) Seq, itemid, category, transid, ... ,@last:=concat(itemid,category) as TMPLast from item_trans order by concat(itemid,category); Now you can use the Alter statement to add your indexes and get rid of the TMPLast column. To build the item_seq table you would now use: create table item_seq select seq, itemid, category from new_item_trans group by seq, itemid, category; And of course build your indexes on seq and rename the new_item_trans. I guarantee you this last solution will not take 9 days to complete! :-) Mike At 12:32 PM 9/6/2009, Hank wrote: Hello All, I'm reposting this since I didn't get much response the last time, so I'm hoping to reach out again. My correlated update query (see below) was running for 9 days before I killed it. Here is my original question: I have a legacy application which was written using a compound primary key of an item number (non unique) along with a category ID. The combination of the item number and category ID make the records unique. I am in the process of replacing the compound (VARCHAR) keys with an unique integer key in these tables. So I have created an item_seq table and assigned a unique sequence number to each compound key -- it looks like this (all tables are myisam tables, and mysql version 5.0) desc item_seq; +---+--+--+-+-++ | Field | Type | Null | Key | Default | Extra | +---+--+--+-+-++ | seq | int(10) unsigned | NO | PRI | NULL| auto_increment | | itemid| char(11) | NO | MUL | || | category | char(4) | NO | | || +---+--+--+-+-++ I also have my main transactional table with about 180,000,000 rows -- it looks like this: desc item_trans; +-+---+--+-+-+---+ | Field | Type | Null | Key | Default | Extra | +-+---+--+-+-+---+ | seq | int(10) unsigned | NO | MUL | | | | itemid | char(11) | NO | PRI | | | | category| char(4) | NO | PRI | | | | transid | int(10) | NO | PRI | | | Currently the seq field is null for the entire table. So of course, I want to update the main transaction table with the new sequence number. So I've disabled all the keys on the item_trans table -- since I am updating every row, it wouldn't (shouldn't) be using the index anyway. Here is my correlated update query: update item_trans i, item_seq is set i.seq=is.seq where is.itemid=i.itemid and is.category=i.category; If I run an explain on the select version of the update, this is what I get: ++-+--++---++-++---+---+ | id | select_type | table| type | possible_keys | key| key_len | ref| rows | Extra | ++-+--++---++-++---+---+ | 1 | SIMPLE | item_trans| ALL| PRIMARY | NULL | NULL | NULL | 178948797 | | | 1 | SIMPLE | item_seq | eq_ref | itemid| itemid | 20 | g.item_trans.itemid,g.item_trans.category| 1 | | ++-+--++---++-++---+---+ ... which is exactly what I would expect it to do. Update every record of the item_trans table, and do a full index lookup on the items_seq table. SO... I've been running this
Re: Speeding up a pretty simple correlated update query
On Sun, Sep 6, 2009 at 6:01 PM, mos mo...@fastmail.fm wrote: So I've disabled all the keys on the item_trans table -- since I am updating every row, it wouldn't (shouldn't) be using the index anyway. You can't disable unique indexes or primary keys. They are always active. You can only deactivate non-unique indexes. Here are a couple of suggestions. For now drop the index on item_seq.seq and desc.seq. Are you sure you have a compound index on item_seq.itemid and item_seq.category?? do a Show create table item_seq and also Show create table desc to see what you've got. Make sure your my.cnf file has key_buffer_size=500M equal to about 30% of your available memory. You can always reduce it later. Of course there is another way of doing it, if you are willing to have the tail wag the dog. You may kick yourself for not discovering it yourself. :) set @num:=0; set @last:=''; create table new_item_trans select IF(concat(itemid,category),@last, @num:=...@num+1,@num) Seq, itemid, category, transid, ... ,@last:=concat(itemid,category) as TMPLast from item_trans order by concat(itemid,category); Now you can use the Alter statement to add your indexes and get rid of the TMPLast column. To build the item_seq table you would now use: create table item_seq select seq, itemid, category from new_item_trans group by seq, itemid, category; And of course build your indexes on seq and rename the new_item_trans. I guarantee you this last solution will not take 9 days to complete! :-) Mike Hi Mike, Thanks for your reply. First, in my tests, I've created the target table (item_trans) as a copy of the source table with no indexes at all (even no primary key). Once I get the item_seq field populated, I'll go back and re-create the indexes in batch using myisamchk (I've posted about this recently). Second, I like your second creative solution (I never would have come up with that), but in order for it to work, mysql would have to sort 180 million records before creating the table or retrieve them out of the table via the contactenated index, both of which I think will take a long time... but I'll certainly give it a shot tomorrow and let you know how it goes. Thanks again. -Hank
Speeding up a pretty simple correlated update query
Hello All, I have a legacy application which was written using a compound primary key of an item number (non unique) along with a category ID. The combination of the item number and category ID make the records unique. I am in the process of replacing the compound (VARCHAR) keys with an unique integer key in these tables. So I have created an item_seq table and assigned a unique sequence number to each compound key -- it looks like this (all tables are myisam tables, and mysql version 5.0) desc item_seq; +---+--+--+-+-++ | Field | Type | Null | Key | Default | Extra | +---+--+--+-+-++ | seq | int(10) unsigned | NO | PRI | NULL| auto_increment | | itemid| char(11) | NO | MUL | || | category | char(4) | NO | | || +---+--+--+-+-++ I also have my main transactional table with about 180,000,000 rows -- it looks like this: desc item_trans; +-+---+--+-+-+---+ | Field | Type | Null | Key | Default | Extra | +-+---+--+-+-+---+ | seq | int(10) unsigned | NO | MUL | | | | itemid | char(11) | NO | PRI | | | | category| char(4) | NO | PRI | | | | transid | int(10) | NO | PRI | | | Currently the seq field is null for the entire table. So of course, I want to update the main transaction table with the new sequence number. So I've disabled all the keys on the item_trans table -- since I am updating every row, it wouldn't (shouldn't) be using the index anyway. Here is my correlated update query: update item_trans i, item_seq is set i.seq=is.seq where is.itemid=i.itemid and is.category=i.category; If I run an explain on the select version of the update, this is what I get: ++-+--++---++-++---+---+ | id | select_type | table| type | possible_keys | key| key_len | ref| rows | Extra | ++-+--++---++-++---+---+ | 1 | SIMPLE | item_trans| ALL| PRIMARY | NULL | NULL | NULL | 178948797 | | | 1 | SIMPLE | item_seq | eq_ref | itemid| itemid | 20 | g.item_trans.itemid,g.item_trans.category| 1 | | ++-+--++---++-++---+---+ ... which is exactly what I would expect it to do. Update every record of the item_trans table, and do a full index lookup on the items_seq table. SO... I've been running this query to update item_trans, and it's been running for 5 days now. I've also tried running this with the primary key index on the item_trans table (but not the seq index), and that ran slower in my initial tests. Are there any faster ways to update 180 million records with a correlated update query? And I'm fairly certain that trying to do this in PHP one-record at a time would take much longer than a SQL solution. Thanks, -Hank
RE: Speeding up a pretty simple correlated update query
Do you know that if you create seq column on the original table as an auto_increment primary key, it will fill in the numbers automatically? There's no need to create the values on another table and update with a join. Regards, Gavin Towey -Original Message- From: Hank [mailto:hes...@gmail.com] Sent: Wednesday, September 02, 2009 4:35 PM To: mysql@lists.mysql.com Subject: Speeding up a pretty simple correlated update query Hello All, I have a legacy application which was written using a compound primary key of an item number (non unique) along with a category ID. The combination of the item number and category ID make the records unique. I am in the process of replacing the compound (VARCHAR) keys with an unique integer key in these tables. So I have created an item_seq table and assigned a unique sequence number to each compound key -- it looks like this (all tables are myisam tables, and mysql version 5.0) desc item_seq; +---+--+--+-+-++ | Field | Type | Null | Key | Default | Extra | +---+--+--+-+-++ | seq | int(10) unsigned | NO | PRI | NULL| auto_increment | | itemid| char(11) | NO | MUL | || | category | char(4) | NO | | || +---+--+--+-+-++ I also have my main transactional table with about 180,000,000 rows -- it looks like this: desc item_trans; +-+---+--+-+-+---+ | Field | Type | Null | Key | Default | Extra | +-+---+--+-+-+---+ | seq | int(10) unsigned | NO | MUL | | | | itemid | char(11) | NO | PRI | | | | category| char(4) | NO | PRI | | | | transid | int(10) | NO | PRI | | | Currently the seq field is null for the entire table. So of course, I want to update the main transaction table with the new sequence number. So I've disabled all the keys on the item_trans table -- since I am updating every row, it wouldn't (shouldn't) be using the index anyway. Here is my correlated update query: update item_trans i, item_seq is set i.seq=is.seq where is.itemid=i.itemid and is.category=i.category; If I run an explain on the select version of the update, this is what I get: ++-+--++---++-++---+---+ | id | select_type | table| type | possible_keys | key| key_len | ref| rows | Extra | ++-+--++---++-++---+---+ | 1 | SIMPLE | item_trans| ALL| PRIMARY | NULL | NULL | NULL | 178948797 | | | 1 | SIMPLE | item_seq | eq_ref | itemid| itemid | 20 | g.item_trans.itemid,g.item_trans.category| 1 | | ++-+--++---++-++---+---+ ... which is exactly what I would expect it to do. Update every record of the item_trans table, and do a full index lookup on the items_seq table. SO... I've been running this query to update item_trans, and it's been running for 5 days now. I've also tried running this with the primary key index on the item_trans table (but not the seq index), and that ran slower in my initial tests. Are there any faster ways to update 180 million records with a correlated update query? And I'm fairly certain that trying to do this in PHP one-record at a time would take much longer than a SQL solution. Thanks, -Hank The information contained in this transmission may contain privileged and confidential information. It is intended only for the use of the person(s) named above. If you are not the intended recipient, you are hereby notified that any review, dissemination, distribution or duplication of this communication is strictly prohibited. If you are not the intended recipient, please contact the sender by reply email and destroy all copies of the original message. -- MySQL General Mailing List For list archives: http://lists.mysql.com/mysql To unsubscribe:http://lists.mysql.com/mysql?unsub=arch...@jab.org
Re: Speeding up a pretty simple correlated update query
Hello Gavin, That's what I did with the first one-to-one table to create the unique SEQ field mapping to each item/category combination. The problem is on the TRANSACTION table, where there are multiple instances of each item/category. If I just put a auto_increment primary key on that table, I'd get a unique TRANSACTION ID, which is not what I want. I want to populate the transaction table with the new integer seq key created in the first table. I guess I should have stated that my overall objective here is to eventually drop the VARCHAR itemid and category id fields from the transaction table, leaving only the new item sequence id (plus transid) as the primary key. There are many tables throughout the schema that do this, and I would be replacing them all. It's just that this is the largest table, and the correlated update is taking a long time, and I'm looking for a better solution (if one exists). thanks. -Hank On Wed, Sep 2, 2009 at 7:50 PM, Gavin Towey gto...@ffn.com wrote: Do you know that if you create seq column on the original table as an auto_increment primary key, it will fill in the numbers automatically? There's no need to create the values on another table and update with a join. Regards, Gavin Towey -Original Message- From: Hank [mailto:hes...@gmail.com] Sent: Wednesday, September 02, 2009 4:35 PM To: mysql@lists.mysql.com Subject: Speeding up a pretty simple correlated update query Hello All, I have a legacy application which was written using a compound primary key of an item number (non unique) along with a category ID. The combination of the item number and category ID make the records unique. I am in the process of replacing the compound (VARCHAR) keys with an unique integer key in these tables. So I have created an item_seq table and assigned a unique sequence number to each compound key -- it looks like this (all tables are myisam tables, and mysql version 5.0) desc item_seq; +---+--+--+-+-++ | Field | Type | Null | Key | Default | Extra | +---+--+--+-+-++ | seq | int(10) unsigned | NO | PRI | NULL| auto_increment | | itemid| char(11) | NO | MUL | || | category | char(4) | NO | | || +---+--+--+-+-++ I also have my main transactional table with about 180,000,000 rows -- it looks like this: desc item_trans; +-+---+--+-+-+---+ | Field | Type | Null | Key | Default | Extra | +-+---+--+-+-+---+ | seq | int(10) unsigned | NO | MUL | | | | itemid | char(11) | NO | PRI | | | | category| char(4) | NO | PRI | | | | transid | int(10) | NO | PRI | | | Currently the seq field is null for the entire table. So of course, I want to update the main transaction table with the new sequence number. So I've disabled all the keys on the item_trans table -- since I am updating every row, it wouldn't (shouldn't) be using the index anyway. Here is my correlated update query: update item_trans i, item_seq is set i.seq=is.seq where is.itemid=i.itemid and is.category=i.category; If I run an explain on the select version of the update, this is what I get: ++-+--++---++-++---+---+ | id | select_type | table| type | possible_keys | key| key_len | ref| rows | Extra | ++-+--++---++-++---+---+ | 1 | SIMPLE | item_trans| ALL| PRIMARY | NULL | NULL | NULL | 178948797 | | | 1 | SIMPLE | item_seq | eq_ref | itemid| itemid | 20 | g.item_trans.itemid,g.item_trans.category| 1 | | ++-+--++---++-++---+---+ ... which is exactly what I would expect it to do. Update every record of the item_trans table, and do a full index lookup on the items_seq table. SO... I've been running this query to update item_trans, and it's been running for 5 days now. I've also tried running this with the primary key index on the item_trans table (but not the seq index), and that ran slower in my initial
