I wanted to create a notification system like the facebook one and thinking of the structure to realize this system.
I've two tables: notification (id, uid, query, date) and notification_unread (id, nid, uid, date).
I tought to use this the following way:
If I make a comment somewhere, I'll add: my uid, $_SERVER['QUERY_STRING'], NOW() to notification.
With notification_unread I wanted to insert data of posts that hasn't been read yet. In this case nid should refer to the notification id. And only if there may be another new post, data will be inserted in this table. Everytime something has been seen by the user, I'll delete the specific entry from this table.
Well, however I couldn't really figure out, if this approach (including DB Design) of me is somewhere somehow "the wrong" or "too complicated" way
and I couldn't figure out to realize this, because I can't think of a logical way WHEN and HOW to insert data to notification_unread. For instance I don't want to notify myself that I made a new post, after I made it. But I guess I'd still have to insert data to the table?
So, the thing is that I'm trying to insert as much data as needed and realize this most effecient.
I hope you could follow me and would really appreciate any suggestions!
At first glance, it may seem very simple & clean solution but its a downfall afterwards.
As podiluska pointed, its better to have a check field.
You can easily display unread one, but what will happen once a user has check it? You will have to move it in read table which will increase your disk I/O which is the slowest process in any system. You can simply query off last 5 notifications or something.
You may want to create an archive table to move old notifications to archive table. Here important thing will be to maintain that notification table since all the updates will be here. The bigger it becomes, more the performance will suffer. Its a long time effect but you might want to consider the solution now rather than later.
Related
I've been reading through several topics now and did some research about logging changes to a mysql table. First let me explain my situation:
I've a ticket system with a table: 'ticket'
As of now I've created triggers which will enter a duplicate entry in my table: 'ticket_history' which has "action" "user" and "timestamp" as additional columns. After some weeks and testing I'm somewhat not happy with that build since every change is creating a full copy of my row in the history table. I do understand that disk space is cheap and I should not worry about it but in order to retrieve some kind of log or nice looking history for the user is painful, at least for me. Also with the trigger I've written I get a new row in the history even if there is no change. But this is just a design flaw of my trigger!
Here my trigger:
BEFORE UPDATE ON ticket FOR EACH ROW
BEGIN
INSERT INTO ticket_history
SET
idticket = NEW.idticket,
time_arrival = NEW.time_arrival,
idticket_status = NEW.idticket_status,
tmp_user = NEW.tmp_user,
action = 'update',
timestamp = NOW();
END
My new approach in order to avoid having triggers
After spening some time on this topic I came up with an approach I would like to discuss and implement. But first I would have some questions about that:
My idea is to create a new table:
id sql_fwd sql_bwd keys values user timestamp
-------------------------------------------------------------------------
1 UPDATE... UPDATE... status 5 14 12345678
2 UPDATE... UPDATE... status 4 7 12345678
The flow would look like this in my mind:
At first I would select something or more from the DB:
SELECT keys FROM ticket;
Then I display the data in 2 input fields:
<input name="key" value="value" />
<input type="hidden" name="key" value="value" />
Hit submit and give it to my function:
I would start with a SELECT again: SELECT * FROM ticket;
and make sure that the hidden input field == the value from the latest select. If so I can proceed and know that no other user has changed something in the meanwhile. If the hidden field does not match I bring the user back to the form and display a message.
Next I would build the SQL Queries for the action and also the query to undo those changes.
$sql_fwd = "UPDATE ticket
SET idticket_status = 1
WHERE idticket = '".$c_get['id']."';";
$sql_bwd = "UPDATE ticket
SET idticket_status = 0
WHERE idticket = '".$c_get['id']."';";
Having that I run the UPDATE on ticket and insert a new entry in my new table for logging.
With that I can try to catch possible overwrites while two users are editing the same ticket in the same time and for my history I could simply look up the keys and values and generate some kind of list. Also having the SQL_BWD I simply can undo changes.
My questions to that would be:
Would it be noticeable doing an additional select everytime I want to update something?
Do I lose some benefits I would have with triggers?
Are there any big disadvantages
Are there any functions on my mysql server or with php which already do something like that?
Or is there might be a much easier way to do something like that
Is maybe a slight change to my trigger I've now already enough?
If I understad this right MySQL is only performing an update if the value has changed but the trigger is executed anyways right?
If I'm able to change the trigger, can I still prevent somehow the overwriting of data while 2 users try to edit the ticket the same time on the mysql server or would I do this anyways with PHP?
Thank you for the help already
Another approach...
When a worker starts to make a change...
Store the time and worker_id in the row.
Proceed to do the tasks.
When the worker finishes, fetch the last worker_id that touched the record; if it is himself, all is well. Clear the time and worker_id.
If, on the other hand, another worker slips in, then some resolution is needed. This gets into your concept that some things can proceed in parallel.
Comments could be added to a different table, hence no conflict.
Changing the priority may not be an issue by itself.
Other things may be messier.
It may be better to have another table for the time & worker_ids (& ticket_id). This would allow for flagging that multiple workers are currently touching a single record.
As for History versus Current, I (usually) like to have 2 tables:
History -- blow-by-blow list of what changes were made, when, and by whom. This is table is only INSERTed into.
Current -- the current status of the ticket. This table is mostly UPDATEd.
Also, I prefer to write the History directly from the "database layer" of the app, not via Triggers. This gives me much better control over the details of what goes into each table and when. Plus the 'transactions' are clear. This gives me confidence that I am keeping the two tables in sync:
BEGIN; INSERT INTO History...; UPDATE Current...; COMMIT;
I've answered a similar question before. You'll see some good alternatives in that question.
In your case, I think you're merging several concerns - one is "storing an audit trail", and the other is "managing the case where many clients may want to update a single row".
Firstly, I don't like triggers. They are a side effect of some other action, and for non-trivial cases, they make debugging much harder. A poorly designed trigger or audit table can really slow down your application, and you have to make sure that your trigger logic is coordinated between lots of developers. I realize this is personal preference and bias.
Secondly, in my experience, the requirement is rarely "show the status of this one table over time" - it's nearly always "allow me to see what happened to the system over time", and if that requirement exists at all, it's usually fairly high priority. With a ticketing system, for instance, you probably want the name and email address of the users who created, and changed the ticket status; the name of the category/classification, perhaps the name of the project etc. All of those attributes are likely to be foreign keys on to other tables. And when something does happen that requires audit, the requirement is likely "let me see immediately", not "get a database developer to spend hours trying to piece together the picture from 8 different history tables. In a ticketing system, it's likely a requirement for the ticket detail screen to show this.
If all that is true, then I don't think history tables populated by triggers are a good idea - you have to build all the business logic into two sets of code, one to show the "regular" application, and one to show the "audit trail".
Instead, you might want to build "time" into your data model (that was the point of my answer to the other question).
Since then, a new style of data architecture has come along, known as CQRS. This requires a very different way of looking at application design, but it is explicitly designed for reactive applications; these offer much nicer ways of dealing with the "what happens if someone edits the record while the current user is completing the form" question. Stack Overflow is an example - we can see, whilst typing our comments or answers, whether the question was updated, or other answers or comments are posted. There's a reactive library for PHP.
I do understand that disk space is cheap and I should not worry about it but in order to retrieve some kind of log or nice looking history for the user is painful, at least for me.
A large history table is not necessarily a problem. Huge tables only use disk space, which is cheap. They slow things down only when making queries on them. Fortunately, the history is not something you'd use all the time, most likely it is only used to solve problems or for auditing.
It is useful to partition the history table, for example by month or week. This allows you to simply drop very old records, and more important, since the history of the previous months has already been backed up, your daily backup schedule only needs to backup the current month. This means a huge history table will not slow down your backups.
With that I can try to catch possible overwrites while two users are editing the same ticket in the same time
There is a simple solution:
Add a column "version_number".
When you select with intent to modify, you grab this version_number.
Then, when the user submits new data, you do:
UPDATE ...
SET all modified columns,
version_number=version_number+1
WHERE ticket_id=...
AND version_number = (the value you got)
If someone came in-between and modified it, then they will have incremented the version number, so the WHERE will not find the row. The query will return a row count of 0. Thus you know it was modified. You can then SELECT it, compare the values, and offer conflict resolution options to the user.
You can also add columns like who modified it last, and when, and present this information to the user.
If you want the user who opens the modification page to lock out other users, it can be done too, but this needs a timeout (in case they leave the window open and go home, for example). So this is more complex.
Now, about history:
You don't want to have, say, one large TEXT column called "comments" where everyone enters stuff, because it will need to be copied into the history every time someone adds even a single letter.
It is much better to view it like a forum: each ticket is like a topic, which can have a string of comments (like posts), stored in another table, with the info about who wrote it, when, etc. You can also historize that.
The drawback of using a trigger is that the trigger does not know about the user who is logged in, only the MySQL user. So if you want to record who did what, you will have to add a column with the user_id as I proposed above. You can also use Rick James' solution. Both would work.
Remember though that MySQL triggers don't fire on foreign key cascade deletes... so if the row is deleted in this way, it won't work. In this case doing it in the application is better.
Okay, so I have created a ticket system for jobs at work.
There are three tables:
Job:
id|subject|flag|status|deadline|ts
Team:
id|jobID|userID|vocation
and exchange:
id|details|foreignID|table|polyflag|userID|ts
Basically a job is created, inserted into job, the team is built up and inserted into team and any posts and conversation for this particular job is put into exchange.
But what I would like to do is find out if a user has not read any posts in a particular job. Because at the moment, they are having to actually go into the job page, and see if there is anything new in there they havent seen. If their job list is particularly large, this will become a problem.
So if a user posts something new, and they havent loaded the job and seen it, I want to be able to show them that somehow. The problem is I have no idea how I can do it.
Suggestions?
you can add a new table with the user_id,job_id columns, and every time someone views a job you insert it there (only for the 1st time), so you can easily select from this table and see which jobs a user viewed or whether a particular job was seen a user
Create another table called readPostStatus with userID, postID and readStatus.
Then on the posts, all statuses will be false for read status. (There are a number of ways to display these results)
Then when a specific user reads the post, edit the readPostStatus table, marking that userID and postID to true in readStatus
I take it you are interested in users that are part of the team for a job, rather than users creating the job. Also I guess there is a User table (for which userID in Team is a foreign key).
What you essentially want is a view counter, for each User for each Job. This looks like a many to many relationship to me, between the two tables. I would suggest that the best way of doing this is to have another table called UserJob or perhaps something more useful, with the fields: jobID, userID, and viewCount. When the job page is loaded you run a query to check whether a record already exists in this table for the job loaded, by the user loading the page. If not then you create it (and initialise the count to 1). Otherwise you increment the view count.
If you don't care about the count, just whether it has been seen or not, then you don't need to bother incrementing the count. You might like to name the field hasSeen or something, instead of viewCount.
Edit: Forgot to say that you can easily check whether a user has seen a job or not by querying this table, and checking whether a row exists (with hasSeen set to 1). Depending on your structure you might want to have the rows of this table automatically added (with hasSeen set to 0) when a user is assigned to a job.
After seeing the answers on here I came up with my own solution, so just for the record, I will put it in here; as none of the other answers really cut it for me.
Okay. So my aversion from the other answers really stems from the fact that I didnt want to create another table. I hate clogging up my database with meaningless tables, and I wanted a better solution.
So I modifed the table team to:
Team: id|jobID|userID|vocation|exchangeID
Adding the column exchangeID, which basically stores the ID of the latest exchange that this user has read. This is updated everytime the user views a job. Easy enough.
Then to find out how many new posts, I simple grab a list from exchange of all the IDs relating to that job, and find out where in the list my team.exchangeID sits and then return the leftover rows gives me unread posts.
I have then stuck this code (20 lines long approx) into a setInterval that loads the data into a on the job view page, so that now that is automatically updated if anyone posts to a job without the person viewing! Smooth!
Thanks for all your help StackOverflow!
I work on a market research database centric website, developed in PHP and MySQL.
It consists of two big parts – one in which users insert and update own data (let say one table T with an user_id field) and another in which an website administrator can insert new or update existing records (same table).
Obviously, in some cases end users will have their data overridden by the administrator while in other cases, administrator entered data is updated by end users (it is fine both ways).
The requirement is to highlight the view/edit forms with (let’s say) blue if end user was the last to update a certain field or red if the administrator is to “blame”.
I am looking into an efficient and consistent method to implement this.
So far, I have the following options:
For each record in table T, add another one ( char(1) ) in which write ‘U’ if end user inserted/updated the field or ‘A’ if the administrator did so. When the view/edit form is rendered, use this information to highlight each field accordingly.
Create a new table H storing an edit history containing something like user_id, field_name, last_update_user_id. Keep table H up-to-date when fields are updated in main table T. When the view/edit form is rendered, use this information to highlight each form field accordingly.
What are the pros/cons of these options; can you suggest others?
I suppose it just depends how forward-looking you want to be.
Your first approach has the advantage of being very simple to implement, is very straightforward to update and utilize, and also will only increase your storage requirements very slightly, but it's also the extreme minimum in terms of the amount of information you're storing.
If you go with the second approach and store a more complete history, if you need to add an "edit history" in the future, you'll already have things set up for that, and a lot of data waiting around. But if you end up never needing this data, it's a bit of a waste.
Or if you want the best of both worlds, you could combine them. Keep a full edit history but also update the single-character flag in the main record. That way you don't have to do any processing of the history to find the most recent edit, just look at the flag. But if you ever do need the full history, it's available.
Personally, I prefer keeping more information than I think I'll need at the time. Storage space is very cheap, and you never know when it's going to come in handy. I'd probably go even further than what you proposed, and also make it so the edit history keeps track of what they changed, and the before/after values. That can be very handy for debugging, and could be useful in the future depending on the project's exact needs.
Yes, implement an audit table that holds copies of the historical data, by/from whom &c. I work on a system currently that keeps it simple and writes the value changes as simple name-value string pairs along with date and by whom. It requires mandatory master record adjustment, but works well for tracking. You could implement this easily with a trigger.
The best way to audit data changes is through a trigger on the database table. In your case you may want to just update the last person to make the change. Or you may want a full auditing solution where you store the previous values making it easy to restore them if they were made in error. But the key to this is to do this on the database and not through the application. Database changes are often made through sources other than the application and you will want to know if this happened as well. Suppose someone hacked into the database and updated the data, wouldn't you like to be able to find the old data easily or know who did it even if he or she did it through a query window and not through the application? You might also need to know if the data was changed through a data import if you ever have to get large amounts of data at one time.
I'm trying to setup a (I thought) fairly simple versioning system for static html pages on a site. The goal is to keep previous versions of the content, then restore to them if needed (I guess basically creating a new version that's a duplicate of an old one), and optionally to toss out data older than X versions ago.
The table's setup is fairly straightforward:
id
reference_id (string/used to determine what page the item pertains to)
content (document/html page sized amount of data)
e_user (user who changed it last)
e_timestamp (when it was changed)
I just want to have something setup to create a previous version for each edit to the content, then be able to restore to it if needed.
What's the best method for accomplishing this? Should everything be in the same table, or spread across a few different ones?
I read through a few pages on the subject, but a lot of them seemed like overkill for what i'm trying to accomplish (ex http://www.jasny.net/articles/versioning-mysql-data/ )
Are there any platforms/guides about that will help me in this endeavorer?
Ideally you would want everything in the same table with something in your query to get the correct version, however you should be careful how you do this as an inefficient query will put extra load on your server. If normally you would select a single item like this:
SELECT * FROM your_table WHERE id = 42
This would then become:
SELECT * FROM your_table
WHERE id = 42
AND date < '2010-10-12 15:23:24'
ORDER BY date DESC
LIMIT 1
Index (id, e_timestamp) to allow this to perform efficiently.
Selecting multiple rows in a single query is more tricky and requires a groupwise-maximum approach but it can be done.
You can use a technique called "auditing". You would set up audit tables. Then you would either write it into your code or setup triggers on the DB side so that every time a change is made, an entry is added into the appropriate audit table. Then you can go back through the audit table and see things like:
"Oh, yesterday Sue went in and fixed a typo"
"Uh oh, steve wiped out an entire paragraph by accident earlier today while trying to rewrite this section"
Your primary table that stores the data doesn't keep all that data, so it can stay slim. If you ever need to look at that data and say roll stuff back, you can go look in your audit table and do that. You can setup the audit table however you want, so each audit row can have the entire content BEFORE edit, and not just what was edited. That should make "rolling back" fairly easy.
Add a version column and a delete column (bool) and create some functions that compare the versions of rows with the same id. You'll definitely want to be able to easily find the current version and the previous version. To get rid of the data you'll want to write another function that sorts all of the versions of id, figures out which are old enough to be deleted, and marks them for deletion by another function. You'll probably want to have an option to make certain pages immune to deletion or postpone it.
I am having a few issues when people are trying to access a MySQL database and they are trying to update tables with the same information.
I have a webpage written using PHP. In this webpage is a query to check if certain data has been entered into the database. If the data hasn't, then i proceed to insert it. The trouble is that if two people try at the same time, the check might say the data has not been entered yet but when the insert takes place it has been by the other person.
What is the best way to handle this scenario? Can i lock the database to only process my queries first then anothers?
Read up on database transactions. That's probably a better way to handle what you need than running LOCK TABLES.
Manually locking tables is the worst think you could ever do. What happens if the code to unlock them never runs (because the PHP fails, or the user next clicks the next step, walks away from the PC, etc).
One way to minimize this in a web app, and a common mistake devs do, is to have a datagrid full of text boxes of data to edit, with a save button per row or on the whole table. Obviously if the person opens this on Friday and comes back Monday, the data could be wrong and they could be saving over new data. One easy way to fix this is to instead have EDIT buttons on each row, and clicking the button then loads an editing form, this way they are hopefully loading fresh data and can only submit 1 row change at a time.
But even more importantly, you should include a datetime field as a hidden input box, and when they try to submit the data look at the date and decide how old the data is and make a decision how old is too old and to warn or deny the user about their action.
You're looking for LOCK.
http://dev.mysql.com/doc/refman/5.0/en/lock-tables.html
This can be run as a simple mysql_query (or MySQLi::query/prepare).
I'd say it's better to lock specific tables (although you can probably try LOCK TABLES *) that need to be locked rather than the whole database - as nothing will be able to be read. I think you're looking for something like:
LOCK TABLES items;
START TRANSACTION;
INSERT INTO items (name, label) VALUES ('foo', 'bar');
UNLOCK TABLES;
Or in PHP:
mysql_query('LOCK TABLES items');
mysql_query("INSERT INTO items (name, label) VALUES ('foo', 'bar')");
mysql_query('UNLOCK TABLES');
You could check if data has been changed before you edit something. In that case if someone has edited data while other person is doing his edit, he will be informed about it.
Kind of like stackoverflow handles commenting.