I am trying to use mysql event schedule in my application, I have not use it before so i have some confusions.
I want to know if my computer is off on the schedule date, then schedule will continue on next day, after starting my computer?
Like:
my schduled is for beginning at every month (no predefined time set)
if in the above date my computer/Server is off,
will mysql continue scheduled event in next day after turning on my computer/server?
If no, then please suggest a solution.
Hmmmm, have you looked at something like this?
MySQL: Using the Event Scheduler
... or:
How to create MySQL Events
... or even: [MySQL :: MySQL 5.1 Reference Manual: 19.4.1. Event Scheduler Overview](19.4.1. Event Scheduler Overview)?
Also please keep in mind that SQL DBMS servers are written with the rather strong presumption that they will be kept up and operating 24 hours per day with only brief periods of downtime for maintenance or repairs. There is generally very little consideration for operation on machines which are shutdown at night and while not in use.
If you simply store a table of dates and events then your can simply query that table for events which have passed or are upcoming within any range you like ... and you can run the program(s) containing those queries (and performing any appropriate activities based on the results) whenever you start you computer and periodically while it's up and running.
These links refer to a feature of MySQL which is designed to have the server internally execute certain commands (MySQL internal commands, such as re-indexing, creating/updating views, cleaning tables of data which "expires" and so on. I don't know if a MySQL server would attempt to execute all events which have passed during downtime, though it should only be a little bit of work to follow the tutorial, schedule some event for some time (say 15 minutes after the time you expect to hit [Enter]) ... then shutdown your computer (or even just the MySQL server) and go off to lunch. Then come back, start it up and see what happens.
The scheduled event could be something absurdly simple, like inserting the "current" time into some table you set up.
Related
I am using MySQL workbench 6.3 CE. I want to take the snapshots of MySQL status variables.
I want to store the values of status variables after every 1 second during the execution of query.
I can simply show the variables using 'show global status'. But I want to execute it automatically after every 1 second.
You can run a procedure and a query at the same time by having two separate connections. Workbench is a handy tool, but you should learn to use the mysql commandline tool, too.
The query is rather simple. INDEX(l_shipdate) is likely to be the best for it.
The real way to speed up the query (assuming that is your ultimate goal) is to build and maintain a "Summary table" of daily or monthly subtotals. Then sum the sums and sum the counts. Avg is (SUM(sums)/SUM(counts)).
More discussion: http://mysql.rjweb.org/doc.php/summarytables
Be cautious about running (via EVENT or cron) any code that might take longer than the interval time. If it gets behind, it is likely to cascade and bring the server down, or at least slow things down severely. For that reason, I much prefer the WHILE loop.
I have to run a command every day at a different time. The times are known in advance and saved in a MySQL database in the familiar YYYY-MM-DD HH:MM:SS format.
What I thought of:
cron schedule the job for the exact time the first day, then make the script itself modify the crontab entry with the correct time for the next day.
cron scheduling the job at approximately the right time, then make it read the exact time from the database and sleep until then.
cron schedule the job execution every minute, and leave it to the script to determine whether the current date/time corresponds to the right execution time; proceded if it is, exit if not.
at submit the job the first day with at, then make it read the next day's time from the database and resubmit itself for then with at.
Additional info:
The command is a PHP script that composes the message of the day and sends it to all users registered to the website. I can consider other technologies if they solve this problem better. I would like to retain the ability of rebooting the server (outside of the intended execution hour) without worrying too much about jobs getting lost, therefore solutions 1. and 3. look better under this aspect. I'm starting with two commands to be run at two different times of the day, but I could soon end up with dozens more of similar jobs to be scheduled at different times every day, so I would prefer to avoid clutter as much as possible. I'd probably go with option 3 at this point.
The question(s):
Is there a better / preferred / established way of accomplishing this task? Solutions other that those mentioned above are welcome. What are the main drawbacks (of your recommended solution) I should be aware of?
I do believe you need to build your custom application for implementing the logic you want to implement.
Eventually you can use the cron system to start the process or to make sure that the process is running (in case it died or it was killed).
In your place what I would do, is to write a custom PHP program (or python or you name it) that performs the following:
Opens a connection to DB
Checks when the next execution is scheduled
Calculates if it is time to run
if not, it sleeps for X seconds (this depends on your preference)
it it is time to run, it performs its duty
sleeps again, and the loop begins
An alternative would be to check the every time the execution schedule, to check for changes in the schedule.
Another one would be read once and sleep until the execution time, but in this other case you would not catch changes in the schedule
This all depends on you, all in the all the program is an extremely easy one
I ended up using solution 3. above and am quite satisfied with it so far.
All the logic is in the .php file, which is responsible to:
save the current date/time in a variable (e.g. $now)
perform any considerations on it
scan the database in search of a matching date/time
This actually allows for a reasonable degree of flexibility:
I can choose not to run any commands if a certain semaphore file exists:
if (file_exists($filename)) {exit;}
I can set parameters in an option file enabling e.g. debug or test modes:
include parameters.php
if ($debug === true) {error_reporting(E_ALL);}
I can avoid bothering users if it is, let's say, new year's day:
if (date('m-d') == '01-01') {exit;}
I can introduce delays based on custom logic:
if (date('w', strtotime($now)) === '0') {$now = date('Y-m-d H:i:s', strtotime($now . ' +15 minutes'));}
I have to update a row into a table(InnoDB) and then right after select the last registry that I updated and make an insert. If the connection is too slow(for the update statement), can the select statement get the wrong row? Assuming that I'm using two different queries.
Are you using SQL to run your script or are you running it somewhere else? (ex PHP, Python, C#)
A Script from SQL should* always complete one line before moving on to the next but if you're unsure you could call something like the sleep function or the wait delay function to pause before you run your second line.
*I say should as I've seen some extremely rare random cases, usually with longer running queries that don't. If your first job takes a long time to complete it may be worth the effort to schedule the first job in Job Agent, then later that day schedule the second job.
MySQL does not keep records of row insertion order. Any algorithm that's based on last registry that I updated must implement its own means to gather the required information. If it doesn't, it will get the wrong row sooner or later. (Network speed is probably not as relevant as concurrent access.)
Let's say a player's energy is recorded in a table as "20". As he engages in mission, his energy decreases and reaches 0. However, it would be replenish back to "20" the following day. How do the database detect that a new day has arrive and then automatically assign some value in a certain table?
Store in database the time (date and hour) when energy should be restored. Then each time player logs in check if this time passed yet or not. If it has, restore the energy.
Upgrade to MySQL 5.1 and use events. http://dev.mysql.com/tech-resources/articles/mysql-events.html
for people who are using shared hosting like me, go look for "cron jobs" in your control panel and then set your automated task there.
Not at all. Call a stored procedure / execute SQL regularly from OUTSIDE the database.
Use a Trigger that'll run when your condition is verified
How much time does MySQL need to build an index of a table with 30,000,000 entries that are strings of length 256?
At the moment it seems to take hours and I don't know how long I should wait till I conclude that MySql simply failed at building an index.
You may run SHOW PROCESSLIST \G in mysql console to watch its state. I had a similar problem just a couple of hours ago, but my table was much smaller.
Here a list of thread states you will definitely need. After an hour of waiting I realized that ALTER TABLE CREATE INDEX is in Locked state, I needed to restart mysqld and run the statement once again. That time I had index built in 15 minutes.
By the way, I recommend to run index creation from mysql console, GUI tools may add some spices to the process.
it could easily take hours. it all depends on the machine specs, load, etc etc. to see whether it's failed, check something like top or watch your hard drives - if they're going mad it's still indexing.
Depending on your OS you may check for disk activity (i.e. does it reads/writes DB files) to find out if it failed or not.