Optimizing a Query (taking upto 0.1s)

plautzer · October 19, 2009

Hi,

I have following mysql query which takes up 0.1 sec to execute and im wondering if there is a way to optimize that.

All I want to do is to match all data sets in the table with rest of data sets in the table which equal parameters (e.g. WHERE Clause).

The table has about 200 000 data sets right now. So the problem is that it take over 20 000 seconds.

I am using a myISAM index (b-tree) on par1 & par2 (combined), par3 and the date.

$sql =" SELECT         
    Count(id) as sum,
    Sum(If(type = 1 ,1,0)) as type1,
    Sum(If(type = 2 ,1,0)) as type2,
    Sum(If(type = 3 ,1,0)) as type3,
    Sum(If(type = 4 ,1,0)) as type4,
    Sum(If(type = 5 ,1,0)) as type5
  From table1
  WHERE
    (par1 != $par1 and par2 != $par2) and
    (par1  != $par2 and par2  != $par1) and
    par3 = $par3 and
    par4 between 800 and 1000 and
    par5 between 400 and 300 and
    date < '$date' and
    date > DATE_SUB('$date', INTERVAL 5 YEAR)";

the values for the ranges of par4 and par5 vary every time.

Can u give me some advice on how I can speed the query?

Greetz,

plautzer

plautzer · October 20, 2009

Hi,

I realized that I didn't follow the rules... sorry about that!

Here's my Situation:

I have a view created of 4 tables:

select 
rm.id , rm.m_id, m.p1_id, m. p2_id , 
p1.p_st AS p1_st, p2.p_st as p2_st,  m.date, m.type , s.c_id 
from 
table1  rm 
left join table2 m  on (rm.m_id = m.id) 
left join table3 p1  on (rm.p_id = p1.id) 
left join table3 p2  on (rm.p_id = p2.id)
left join table4 s     on (m.s_id = s.id);

The view holds currently about 250 000 data sets. Now i like to run following query:

SELECT         
    Count(id) as sum,
    Sum(If(type = 1 ,1,0)) as type1,
    Sum(If(type = 2 ,1,0)) as type2,
    Sum(If(type = 3 ,1,0)) as type3,
    Sum(If(type = 4 ,1,0)) as type4,
    Sum(If(type = 5 ,1,0)) as type5
  From table1
  WHERE
    (p1_id != 258 and p2_id != 248) and
    (p1_id  != 248 and p2_id  != 258) and
    c_id != 43 and
    p1_st between 800 and 1200 and
    p2_st between 700 and 2300 and
    date < '2008-12-18' and
    date > DATE_SUB('2008-12-18' , INTERVAL 5 YEAR)

Status

starting

Opening tables

System lock

Table lock

init

checking permissions

optimizing

statistics

preparing

executing

Sending data

end

query end

freeing items

logging slow query

cleaning up

Endurance (query in phpmyadmin)

0.000083

0.000379

0.000008

0.000005

0.000003

0.000054

0.000022

0.000240

0.000020

0.000004

3.403.687

0.000009

0.000005

0.000067

0.000004

0.000008

Status

starting

Opening tables

System lock

Table lock

init

checking permissions

optimizing

statistics

preparing

executing

end

query end

freeing items

logging slow query

cleaning up

Endurance(explain in phpmyadmin)

0.000084

0.000349

0.000007

0.000016

0.000006

0.000003

0.000054

0.000027

0.000231

0.000019

0.000026

0.000007

0.000003

0.000028

0.000003

0.000006

The rest of Explain statement:

phpMyAdmin 3.2.0.1 / MySQL 5.1.37

5rows:

id

1

select_type

SIMPLE

table

rm

m

s

p1

p2

type

ALL

eq_ref

possible_keys

p1_st,p2_st,m_id

PRIMARY,season_id,date,p1_id

PRIMARY,c_id

PRIMARY,p_st

key

NULL

PRIMARY

key_len

NULL

4

ref

NULL

new_old.rm.m_id

new_old.m.s_id

new_old.rm.p_id

rows

250000

1

Extra

Using where

The Problem is that it take far too lang to execute the query when I am looping it about 200 000 times. Can u give me a hint how I might improve it?

Here's my mysql.ini:

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1

kickstart · October 20, 2009

Hi

Do you have to execute it that many times, or can you use GROUP BY and execute it once? Probably comes down to the values of $par1 and $par2.

All the best

Keith

plautzer · October 20, 2009

Do you have to execute it that many times, or can you use GROUP BY and execute it once? Probably comes down to the values of $par1 and $par2.

Right... all the parameters change with every loop... therefore i guess its pretty difficult to do it in one loop.

In your experience... how fast can I possibly process such query - under 0.001s?

Mchl · October 20, 2009

Even if you cut down query execution time, sending data to and from mysql 200k times will still take a considerable amount of time, and there's nothing you can do about it.

Perhaps tell us what is this query doing, so that we might think on how to eliminate the need to loop it.

kickstart · October 20, 2009

Hi

Bit nasty then, unless the parameters come from another table and you could do a JOIN of some kind.

Only other thing to do would be to use a COUNT to draw out the counts of each type and to then manually sum up the count of ID when looping through the returned records. This might be more efficient than trying to do IF statements on numerous rows.

All the best

Keith

Mchl · October 20, 2009

Just run this code

$mysqli = new mysqli('localhost','root','','test');
$time1 = microtime(true);
for ($i = 1; $i <= 200000; $i++) {
$result = $mysqli->query('SELECT 1');
$row = $result->fetch_assoc();
}

$time2 = microtime(true);

echo "Elapsed time: ".($time2 - $time1)."s";

on my PC. One can hardly imagine simpler query, and it still took over 25 seconds. When I changed the query to 'SELECT * FROM t1', where t1 has 5 rows in two columns, elapsed time exceeded 40 seconds.

plautzer · October 20, 2009

Perhaps tell us what is this query doing, so that we might think on how to eliminate the need to loop it.

I want to crossmatch all data sets within the table (or view) and take some statistics.

It works like this...

when I am adding a new data sets with various parameter I want to count all the similiar data sets within the table that:

- lie within a 5 year period

- have simliar p1_st

and different id (p1_id, p2_id, c_id)

This query takes me hours crossmatch all... therefore I thought to do that with arrays (http://www.phpfreaks.com/forums/index.php/topic,273430.0.html) if the query optimization isnt working.

kickstart · October 20, 2009

Hi

I think I would need more to go on (such as where the various parms come from), but suspect you could do this using a cross join of your view against itself.

Ie, base it on something like this (probably a few typos but hopefully gives you the right idea):-

SELECT *
FROM table1 a
CROSS JOIN table1 b
WHERE b.p1_st between 800 and 1200 
and b.p2_st between 700 and 2300 
and a.date BETWEEN DATE_SUB('2008-12-18' , INTERVAL 5 YEAR) AND '2008-12-18'
and b.date BETWEEN DATE_SUB('2008-12-18' , INTERVAL 5 YEAR) AND '2008-12-18'
AND a.p1_id != b.p1_id
AND a.p2_id != b.p2_id
AND a.id != b.id

All the best

Keith

plautzer · October 20, 2009

looks good... i could store the parameter in the db as well...

I have 2 questions thou:

- Can I put the count just in the select statement?

- why did put in the date twice

I thought of something like this:

select id, sum, type1,... 
from (
SELECT         
    Count(id) as sum,
    Sum(If(type = 1 ,1,0)) as type1,
    Sum(If(type = 2 ,1,0)) as type2,
    Sum(If(type = 3 ,1,0)) as type3,
    Sum(If(type = 4 ,1,0)) as type4,
    Sum(If(type = 5 ,1,0)) as type5
  From table1
  WHERE
    (p1_id != this->p1_id and p2_id != this->p2_id) and
    (p1_id  != this->p2_id and p2_id  != this->p1_id) and
    c_id != this->c_id and
    p1_st between this->p1_st1 and this->p1_st2 and
    p2_st between this->p2_st1 and this->p2_st2 and
    date < this->date and
    date > DATE_SUB(this->date , INTERVAL 5 YEAR)  
)

"this->" is supposed to be the parameters from the outer select

kickstart · October 20, 2009

Hi

You could put the counts something like this:-

SELECT a.id, Count(b.id) as sum,
    Sum(If(b.type = 1 ,1,0)) as type1,
    Sum(If(b.type = 2 ,1,0)) as type2,
    Sum(If(b.type = 3 ,1,0)) as type3,
    Sum(If(b.type = 4 ,1,0)) as type4,
    Sum(If(b.type = 5 ,1,0)) as type5
FROM table1 a
CROSS JOIN table1 b
WHERE b.p1_st between 800 and 1200 
and b.p2_st between 700 and 2300 
and a.date BETWEEN DATE_SUB('2008-12-18' , INTERVAL 5 YEAR) AND '2008-12-18'
and b.date BETWEEN DATE_SUB('2008-12-18' , INTERVAL 5 YEAR) AND '2008-12-18'
AND a.p1_id != b.p1_id
AND a.p2_id != b.p2_id
AND a.id != b.id
GROUP BY a.id

Reason I put date twice is I have assumed you have pseudo coded it as though you have a column on the table called date and you are only interested in those records within 5 years, and as the table is joined against itself you need to only deal with records within 5 years on both copies of itself.

All the best

Keith

plautzer · October 20, 2009

I tried the query and made following observation:

- results are only shown if there is a least one hit (or count)

- it doesn't work well with the view (takes an hour with 10 000 data sets)

- if I put all parameters in one table:

+- it works extremely fast with 50 000 data sets (about 8 seconds)

+- and somehow really slow with 100 000 data sets (over an hour)

Do u have clue why this might be?

Here are some parameters I changed in my my.ini:

key_buffer              = 500M
max_allowed_packet      = 1M
table_cache             = 256
sort_buffer_size        = 512K
net_buffer_length       = 8K
read_buffer_size        = 256K
read_rnd_buffer_size    = 512K
myisam_sort_buffer_size = 128M

[myisamchk]
key_buffer = 40M
sort_buffer_size = 40M
read_buffer = 40M
write_buffer = 40M

greetz,

Plautzer

kickstart · October 20, 2009

Hi

Issue with nothing unless there is 1 hit could probably be solved by removing the line saying AND a.id != b.id. This would mean you always get one which would be the row itself, and every count would include it (shouldn't be a problem as long as you realise this when using the results).

With 50k it will generate 2,500,000,000 records from the initial join. With 100k it will generate 10,000,000,000 records from the initial join. Ramps up rapidly. You could possibly exclude some records from the "b" part of the statement prior to the join (ie, both based on the date and the checks for p1_st and p2_st). I take it from your comments you have dropped the view and just put the full selects into this code? If so should be easy enough.

Even at an hour for 100k records it appears to be far faster than your initial loop.

All the best

Keith

plautzer · October 21, 2009

Hi,

Even at an hour for 100k records it appears to be far faster than your initial loop.

its faster than calling the loop from the php script.

What I dont get is why a mysql query would be faster than looping thru an array. I could narrow the inner loop down to a lest 5000 loops instead of 100k. The would be 500 million records in an array loop compared to 10 billion records in the query. So the array should be 20 times faster?!

Is there a way to calculate the time which an array/mysql query would need to process? I wanna know whats minimal time usage... so that I dont go nuts optimizing

You could possibly exclude some records from the "b" part of the statement prior to the join (ie, both based on the date and the checks for p1_st and p2_st). I take it from your comments you have dropped the view and just put the full selects into this code? If so should be easy enough.

Yea, I replaced the view with a table. I'll try taking the IDs and date in the join (on)... but how does that speed up the query?

Does it matter which engine I use? MyISAM oder Innodb?

Thx, I appreciate the help!

Plautzer

kickstart · October 21, 2009

Hi

You are dealing with massive sets of data, and SQL is optimised for dealing with them. While php is a comparatively slow interpretted language. If you keep passing different pieces of SQL to the database then it is having to interpret it each time, rather than just once.

On top of that you could possibly be experiencing delays from network traffic is you db is on one server and your script on another.

Excluding rows before the JOIN might help as it will reduce the size of the intermediate table that is generated. Ie, if you have 100k records and join it to itself you get 10,000,000,000. If you can exclude half the records from the copy you are joining to then you reduce that to 5,000,000,000

Not sure on the db engine.

All the best

Keith

plautzer · October 21, 2009

Excluding rows before the JOIN might help as it will reduce the size of the intermediate table that is generated.

I am not sure what u mean by excluding. Do I exlcude rows before a join when I put some exceptions in the join condition (Ie join on aid = sid and number > 1000 and ...) ?? Until now i thought that there is no difference putting additional conditions in the join condition or in the where condition.

Greetz

Plautzer

kickstart · October 21, 2009

Hi

Normally best not, but when you are doing a cross join you are generating an intermediate table that has a number of rows that is the square of the original number. If you can reduce the rows before joining against itself it should make a large difference.

All the best

Keith

plautzer · October 21, 2009

to be clear, this means that I have to reduce the rows of table b for each record in table a by finding the records in b that lie within the date range: (in my case that would reduce the table b to 1000-20000 records depending on the date of table a)

SELECT a.id, Count(b.id) as sum,
    Sum(If(b.type = 1 ,1,0)) as type1,
    Sum(If(b.type = 2 ,1,0)) as type2,
    Sum(If(b.type = 3 ,1,0)) as type3,
    Sum(If(b.type = 4 ,1,0)) as type4,
    Sum(If(b.type = 5 ,1,0)) as type5
FROM table1 a
CROSS JOIN table1 b on (b.date BETWEEN DATE_SUB('2008-12-18' , INTERVAL 5 YEAR) AND '2008-12-18')
WHERE 
b.p1_st between 800 and 1200
and b.p2_st between 700 and 2300
AND a.p1_id != b.p1_id
AND a.p2_id != b.p2_id
AND a.id != b.id
GROUP BY a.id

If i got that right... why not putting all the conditions in join?

SELECT a.id, Count(b.id) as sum,
    Sum(If(b.type = 1 ,1,0)) as type1,
    Sum(If(b.type = 2 ,1,0)) as type2,
    Sum(If(b.type = 3 ,1,0)) as type3,
    Sum(If(b.type = 4 ,1,0)) as type4,
    Sum(If(b.type = 5 ,1,0)) as type5
FROM table1 a
CROSS JOIN table1 b on 
(b.date BETWEEN DATE_SUB('2008-12-18' , INTERVAL 5 YEAR) AND '2008-12-18' and
b.p1_st between 800 and 1200
and b.p2_st between 700 and 2300
AND a.p1_id != b.p1_id
AND a.p2_id != b.p2_id
AND a.id != b.id)
GROUP BY a.id

Mchl · October 21, 2009

MyISAM and InnoDB are comparatively fast these days.

kickstart · October 21, 2009

Hi

To be honest I have never used an ON clause in a CROSS JOIN (as it doesn't appear logical with what cross joins are meant to be used for, but may well work). However if it works then is would appear to be an easy way of what I was suggesting.

If not then something like this:-

SELECT a.id, Count(b.id) as sum,
    Sum(If(b.type = 1 ,1,0)) as type1,
    Sum(If(b.type = 2 ,1,0)) as type2,
    Sum(If(b.type = 3 ,1,0)) as type3,
    Sum(If(b.type = 4 ,1,0)) as type4,
    Sum(If(b.type = 5 ,1,0)) as type5
FROM table1 a
CROSS JOIN (SELECT * FROM table1 
WHERE date BETWEEN DATE_SUB('2008-12-18' , INTERVAL 5 YEAR) AND '2008-12-18' 
and p1_st between 800 and 1200
and p2_st between 700 and 2300) b
WHERE a.p1_id != b.p1_id
AND a.p2_id != b.p2_id
AND a.id != b.id
GROUP BY a.id

All the best

Keith

plautzer · October 21, 2009

Hi,

i tried different versions of the query but it doesnt work out too great. I also tried a left which got me the 0 records as well but it takes about 4 minutes for 1 000 000 records and over 15 min for 64 000 000. So over 100 billion would take hours.

I thought of another solution where I categorize p1_st in quadrants... ie i have x quadrants that a different ranges like 0-500, 501-100, 1001... that would help narrowing down the search in certain quadrant.. with only a percentage of 250 k records to look in.

Does that make sense for a database query?

If so... do u have clue how i could realize that?

greetz

Plautzer

kickstart · October 21, 2009

Hi

It would help to cut it down into quadrants (you could just assign the quadrants a number and check that they are equal in the ON clause), but it you are trying to id records that are close to each other then not sure if it would help.

Whatever you do with 100 billion records would take ages.

Do you really need you app to process this number of records?

All the best

Keith

plautzer · October 22, 2009

well, its a statistical counting therefore i have to process all of them.

some thoughts..

I would be a lot easier if I could relate to previous record and just add the count and type or i had some kind of formula where i could calculate the result from... but this seems to be impossible since the range of p1_st, p2_st and the date changes every time.

And even if I fix ranges of p1_st, p2_st there is still the date that cannot. Or do u see other possiblities?

Another thought is if stored procedures/functions would help me out here? i could run the statistics on insert of a record an calculate do the count right away. the advantage i see is that the database doesnt always have to thru the whole db because its amount of records increases slowly on every insert.

Greetz,

Plautzer

Mchl · October 22, 2009

You can use triggers to perform an action on every insert.

kickstart · October 22, 2009

Mchls suggestion sounds best.

You could insert / update to a stats table on each insert, and then just process that when you require the stats.

All the best

Keith

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