I know i am writing query's wrong and when we get a lot of traffic, our database gets hit HARD and the page slows to a grind...
I think I need to write queries based on CREATE VIEW from the last 30 days from the CURDATE ?? But not sure where to begin or if this will be MORE efficient query for the database?
Anyways, here is a sample query I have written..
$query_Recordset6 = "SELECT `date`, title, category, url, comments
FROM cute_news
WHERE category LIKE '%45%'
ORDER BY `date` DESC";
Any help or suggestions would be great! I have about 11 queries like this, but I am confident if I could get help on one of these, then I can implement them to the rest!!
Putting a wildcard on the left side of a value comparison:
LIKE '%xyz'
...means that an index can not be used, even if one exists. Might want to consider using Full Text Searching (FTS), which means adding full text indexing.
Normalizing the data would be another step to consider - categories should likely be in a separate table.
SELECT `date`, title, category, url, comments
FROM cute_news
WHERE category LIKE '%45%'
ORDER BY `date` DESC
The LIKE '%45%' means a full table scan will need to be performed. Are you perhaps storing a list of categories in the column? If so creating a new table storing category and news_article_id will allow an index to be used to retrieve the matching records much more efficiently.
OK, time for psychic debugging.
In my mind's eye, I see that query performance would be improved considerably through database normalization, specifically by splitting the category multi-valued column into a a separate table that has two columns: the primary key for cute_news and the category ID.
This would also allow you to directly link said table to the categories table without having to parse it first.
Or, as Chris Date said: "Every row-and-column intersection contains exactly one value from the applicable domain (and nothing else)."
Anything with LIKE '%XXX%' is going to be slow. Its a slow operation.
For something like categories, you might want to separate categories out into another table and use a foreign key in the cute_news table. That way you can have category_id, and use that in the query which will be MUCH faster.
Also, I'm not quite sure why you're talking about using CREATE VIEW. Views will not really help you for speed. Not unless its a materialized view, which MySQL doesn't suppose natively.
If your database is getting hit hard, the solution isn't to make a view (the view is still basically the same amount of work for the database to do), the solution is to cache the results.
This is especially applicable since, from what it sounds like, your data only needs to be refreshed once every 30 days.
I'd guess that your category column is a list of category values like "12,34,45,78" ?
This is not good relational database design. One reason it's not good is as you've discovered: it's incredibly slow to search for a substring that might appear in the middle of that list.
Some people have suggested using fulltext search instead of the LIKE predicate with wildcards, but in this case it's simpler to create another table so you can list one category value per row, with a reference back to your cute_news table:
CREATE TABLE cute_news_category (
news_id INT NOT NULL,
category INT NOT NULL,
PRIMARY KEY (news_id, category),
FOREIGN KEY (news_id) REFERENCES cute_news(news_id)
) ENGINE=InnoDB;
Then you can query and it'll go a lot faster:
SELECT n.`date`, n.title, c.category, n.url, n.comments
FROM cute_news n
JOIN cute_news_category c ON (n.news_id = c.news_id)
WHERE c.category = 45
ORDER BY n.`date` DESC
Any answer is a guess, show:
- the relevant SHOW CREATE TABLE outputs
- the EXPLAIN output from your common queries.
And Bill Karwin's comment certainly applies.
After all this & optimizing, sampling the data into a table with only the last 30 days could still be desired, in which case you're better of running a daily cronjob to do just that.
Related
As i am a junior PHP Developer growing day by day stuck in a performance problem described here:
I am making a search engine in PHP ,my database has one table with 41 column and million's of rows obviously it is a very large dataset. In index.php i have a form for searching data.When user enters search keyword and hit submit the action is on search.php with results.The query is like this.
SELECT * FROM TABLE WHERE product_description LIKE '%mobile%' ORDER BY id ASC LIMIT 10
This is the first query.After result shows i have to run 4 other query like this:
SELECT DISTINCT(weight_u) as weight from TABLE WHERE product_description LIKE '%mobile%'
SELECT DISTINCT(country_unit) as country_unit from TABLE WHERE product_description LIKE '%mobile%'
SELECT DISTINCT(country) as country from TABLE WHERE product_description LIKE '%mobile%'
SELECT DISTINCT(hs_code) as hscode from TABLE WHERE product_description LIKE '%mobile%'
These queries are for FILTERS ,the problem is this when i submit search button ,all queries are running simultaneously at the cost of Performance issue,its very slow.
Is there any other method to fetch weight,country,country_unit,hs_code speeder or how can achieve it.
The same functionality is implemented here,Where the filter bar comes after table is filled with data,How i can achieve it .Please help
Full Functionality implemented here.
I have tried to explain my full problem ,if there is any mistake please let me know i will improve the question,i am also new to stackoverflow.
Firstly - are you sure this code is working as you expect it? The first query retrieves 10 records matching your search term. Those records might have duplicate weight_u, country_unit, country or hs_code values, so when you then execute the next 4 queries for your filter, it's entirely possible that you will get values back which are not in the first query, so the filter might not make sense.
if that's true, I would create the filter values in your client code (PHP)- finding the unique values in 10 records is going to be quick and easy, and reduces the number of database round trips.
Finally, the biggest improvement you can make is to use MySQL's fulltext searching features. The reason your app is slow is because your search terms cannot use an index - you're wild-carding the start as well as the end. It's like searching the phonebook for people whose name contains "ishra" - you have to look at every record to check for a match. Fulltext search indexes are designed for this - they also help with fuzzy matching.
I'll give you some tips that will show useful in many situations when querying a large dataset, or mostly any dataset.
If you can list the fields you want instead of querying for '*' is a better practice. The weight of this increases as you have more columns and more rows.
Always try to use the PK's to look for the data. The more specific the filter, the less it will cost.
An index in this kind of situation would come pretty handy, as it will make the search more agile.
LIKE queries are generally pretty slow and resource heavy, and more in your situation. So again, the more specific you are, the better it will get.
Also add, that if you just want to retrieve data from this tables again and again, maybe a VIEW would fit nicely.
Those are just some tips that came to my mind to ease your problem.
Hope it helps.
Hi, I am creating a simple news website and I need to count news views. Currently I have 25000 rows and 25 columns. The hits count increases per page reload like Joomla. How should I structure the tables?
I have 2 approaches to this issue:
Create column named hits in the content table.
Create a new table that has 2 columns: content_id and hits.
I used the first approach and I think that slows my site.Will the second approaches perform better than the first one? Is there a better approach?
Well I don't know what's your logic in MySQL or PHP or what is you current table structure for news but I would suggest you to use Stored Procedure in MySQL as
Begin
update tblnews set hits = hits+1;
select news from tblnews;
End
and off course use PHP PDO Prepared Statement for performance
and if you are trying to get last 10 news or something like that then must set Indexing for content_id say like Primary key with auto_increment for better retrieval of query otherwise don't even use content_id column. I don't think there should be any hard structre for table. This would definitely increase performance and more than 100000000 rows would not make any big difference I hope. I don't think there would be any other better solution because these 2 queries needs to be performed at every page view.
Option 1 sounds the best. Option 2 is redundant because your just storing the hits. Again you would a join query to pull the hits
I have a table in MySQL that I'm accessing from PHP. For example, let's have a table named THINGS:
things.ID - int primary key
things.name - varchar
things.owner_ID - int for joining with another table
My select statement to get what I need might look like:
SELECT * FROM things WHERE owner_ID = 99;
Pretty straightforward. Now, I'd like users to be able to specify a completely arbitrary order for the items returned from this query. The list will be displayed, they can then click an "up" or "down" button next to a row and have it moved up or down the list, or possibly a drag-and-drop operation to move it to anywhere else. I'd like this order to be saved in the database (same or other table). The custom order would be unique for the set of rows for each owner_ID.
I've searched for ways to provide this ordering without luck. I've thought of a few ways to implement this, but help me fill in the final option:
Add an INT column and set it's value to whatever I need to get rows
returned in my order. This presents the problem of scanning
row-by-row to find the insertion point, and possibly needing to
update the preceding/following rows sort column.
Having a "next" and "previous" column, implementing a linked list.
Once I find my place, I'll just have to update max 2 rows to insert
the row. But this requires scanning for the location from row #1.
Some SQL/relational DB trick I'm unaware of...
I'm looking for an answer to #3 because it may be out there, who knows. Plus, I'd like to offload as much as I can on the database.
From what I've read you need a new table containing the ordering of each user, say it's called *user_orderings*.
This table should contain the user ID, the position of the thing and the ID of the thing. The (user_id, thing_id) should be the PK. This way you need to update this table every time but you can get the things for a user in the order he/she wants using ORDER BY on the user_orderings table and joining it with the things table. It should work.
The simplest expression of an ordered list is: 3,1,2,4. We can store this as a string in the parent table; so if our table is photos with the foreign key profile_id, we'd place our photo order in profiles.photo_order. We can then consider this field in our order by clause by utilizing the find_in_set() function. This requires either two queries or a join. I use two queries but the join is more interesting, so here it is:
select photos.photo_id, photos.caption
from photos
join profiles on profiles.profile_id = photos.profile_id
where photos.profile_id = 1
order by find_in_set(photos.photo_id, profiles.photo_order);
Note that you would probably not want to use find_in_set() in a where clause due to performance implications, but in an order by clause, there are few enough results to make this fast.
I pull a range (e.g. limit 72, 24) of games from a database according to which have been voted most popular. I have a separate table for tracking game data, and one for tracking individual votes for a game (rating from 1 to 5, one vote per user per game). A game is considered "most popular" or "more popular" when that game has the highest average rating of all the rating votes for said game. Games with less than 5 votes are not considered. Here is what the tables look like (two tables, "games" and "votes"):
games:
gameid(key)
gamename
thumburl
votes:
userid(key)
gameid(key)
rating
Now, I understand that there is something called an "index" which can speed up my queries by essentially pre-querying my tables and constructing a separate table of indices (I don't really know.. that's just my impression).
I've also read that mysql operates fastest when multiple queries can be condensed into one longer query (containing joins and nested select statements, I presume).
However, I am currently NOT using an index, and I am making multiple queries to get my final result.
What changes should be made to my database (if any -- including constructing index tables, etc.)? And what should my query look like?
Thank you.
Your query that calculates the average for every game could look like:
SELECT gamename, AVG(rating)
FROM games INNER JOIN votes ON games.gameid = votes.gameid
GROUP BY games.gameid
HAVING COUNT(*)>=5
ORDER BY avg(rating) DESC
LIMIT 0,25
You must have an index on gameid on both games and votes. (if you have defined gameid as a primary key on table games that is ok)
According to the MySQL documentation, an index is created when you designate a primary key at table creation. This is worth mentioning, because not all RDBMS's function this way.
I think you have the right idea here, with your "votes" table acting as a bridge between "games" and "user" to handle the many-to-many relationship. Just make sure that "userid" and "gameid" are indexed on the "votes" table.
If you have access to use InnoDB storage for your tables, you can create foreign keys on gameid in the votes table which will use the index created for your primary key in the games table. When you then perform a query which joins these two tables (e.g. ... INNER JOIN votes ON games.gameid = votes.gameid) it will use that index to speed things up.
Your understanding of an index is essentially correct — it basically creates a separate lookup table which it can use behind the scenes when the query is executed.
When using an index it is useful to use the EXPLAIN syntax (simply prepend your SELECT with EXPLAIN to try this out). The output it gives show you the list of possible keys available for the query as well as which key the query is using. This can be very helpful when optimising your query.
An index is a PHYSICAL DATA STRUCTURE which is used to help speed up retrieval type queries; it's not simply a table upon a table -> good for a concept though. Another concept is the way indexes work at the back of your text book (the only difference is with your book a search key could point to multiple pages / matches whereas with indexes a search key points to only one page/match). An index is defined by data structures so you could use a B+ tree index and there are even hash indexes. It's Database/Query optimization from the physical/internal level of the Database - I'm assuming that you know that you're working at the higher levels of the DBMS which is easier. An index is rooted within the internal levels and that make DB query optimization much more effective and interesting.
I've noticed from your question that you have not even developed the query as yet. Focus on the query first. Indexing comes after, as a matter of a fact, in any graduate or post graduate Database course, indexing falls under the maintenance of a Database and not necessarily the development.
Also N.B. I have seen quite many people say as a rule to make all primary keys indexes. This is not true. There are many instances where a primary key index would slow up the Database. Infact, if we were to go with only primary indexes then should use hash indexes since they work better than B+ trees!
In summary, it doesn't make sense to ask a question for a query and an index. Ask for help with the query first. Then given your tables (relational schema) and SQL query, then and only then could I advice you on the best index - remember its maintenance. We can't do maintanance if there is 0 development.
Kind Regards,
N.B. most questions concerning indexes at the post graduate level of many computing courses are as follows: we give the students a relational schema (i.e. your tables) and a query and then ask: critically suggest a suitable index for the following query on the tables ----> we can't ask a question like this if they dont have a query
I want to list the recent activities of a user on my site without doing too many queries. I have a table where I list all the things the user did with the date.
page_id - reference_id - reference_table - created_at - updated_at
The reference_id is the ID I need to search for in the reference_table (example: comments). If I would do a SELECT on my activity table I would then have to query:
SELECT * FROM reference_table where id = reference_id LIMIT 1
An activity can be a comment, a page update or a subscription. Depending which one it is, I need to fetch different data from other tables in my database
For example if it is a comment, I need to fetch the author's name, the comment, if it is a reply I need to fetch the orignal comment username, etc.
I've looked into UNION keyword to union all my tables but I'm getting the error
1222 - The used SELECT statements have a different number of columns
and it seems rather complicated to make it work because the amount of columns has to match and none of my table has the same amount of tables and I'm not to fond of create column for the fun of it.
I've also looked into the CASE statement which also requires the amount of columns to match if I remember correctly (I could be wrong for this one though).
Does anyone has an idea of how I could list the recent activities of a user without doing too many queries?
I am using PHP and MySQL.
You probably want to split out the different activities into different tables. This will give you more flexiblity on how you query the data.
If you choose to use UNION, make sure that the you use the same number of columns in each select query that the UNION is comprised of.
EDIT:
I was down-voted for my response, so perhaps I can give a better explanation.
Split Table into Separate Tables and UNION
I recommended this technique, because it will allow you to be more explicit about the resources for which you are querying. Having a single table for inserting is convenient, but you will always have to do separate queries to join with other tables to get meaningful information. Also, you database schema will be obfuscated by a single column being a foreign key for different tables depending on the data stored in that row.
You could have tables for comment, update and subscription. These would have their own data which could be queried on individually. If, say, you wanted to look at ALL user activity, you could somewhat easily use a UNION as follows:
(SELECT 'comment', title, comment_id AS id, created FROM comment)
UNION
(SELECT 'update', title, update_id as id, created FROM update)
UNION
(SELECT 'subscription', title, subscription_id as id, created
FROM subscription)
ORDER BY created desc
This will provide you with a listing view. You could then link to the details of each type or load it on an ajax call.
You could accomplish this with the method that you are currently using, but this will actually eliminate the need for the 'reference_table' and will accomplish the same thing in a cleaner way (IMO).
The problem is that UNION should be used just to get similar recordsets together. If you try to unify two different queries (for example, with different columns being fetched) it's an error.
If the nature of the queries is different (having different column count, or data types) you'll need to make several different queries and treat them all separately.
Another approach (less elegant, I guess) would be LEFT JOINing your activities table with all the others, so you'll end up with a recordset with a lot of columns, and you'll need to check for each row which columns should be used depending on the activity nature.
Again, I'd rather stick with the first one, since the second procudes a rather sparse recorset.
With UNION you don't have to get all of the columns from each table, just as long as all of the columns have the same datatypes.
So you could do something like this:
SELECT name, comment as description
FROM Comments
UNION
SELECT name, reply as description
FROM Replies
And it wouldn't matter if Comments and Replies have the same number of columns.
This really depends on the amount of traffic on your site. The union approach is a straightforward and possibly the correct one, logically, but you'll suffer on the performance if your site is heavily loaded since the indexing of a UNIONed query is hard.
Joining might be good, but again, in terms of performance and code clarity, it's not the best of ways.
Another totally different approach is to create an 'activities' table, which will be updated with activity (in addition to the real activity, just for this purpose). In old terms of DB correctness, you should avoid this approach since it will create duplicate data on your system, I, however, found it very useful in terms of performance.
[Another side note about the UNION approach if you decide to take it: if you have difference in parameters length, you can SELECT bogus parameters on some of the unions, for example.. (SELECT UserId,UserName FROM users) UNION (SELECT 0,UserName from notes)