I have a MySQL database on my server, and a Windows WPF application from which my clients will be inserting and deleting rows corresponding to their data. There may be hundreds of users working on the application at the same time, and they will be inserting or deleting rows in the db.
My question is whether or not all the database execution can go successfully or should I adapt some other alternative?
PS: There won't be any clash on rows while insertion/deletion by users as a user will be able to add/remove his/her corresponding data only.
My question is whether or not all the database execution can go successfully ...
Yes, like most other relational database systems, MySQL supports concurrent inserts, updates and deletes so this shouldn't be an issue provided that the operations don't conflict with each other.
If they do, you need to find a way to manage concurrency.
MySQL concurrency, how does it work and do I need to handle it in my application
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I have an application that runs on a MySQL database, the application is somewhat resource intensive on the DB.
My client wants to connect Qlikview to this DB for reporting. I was wondering if someone could point me to a white paper or URL regarding the best way to do this without causing locks etc on my DB.
I have searched the Google to no avail.
Qlikview is in-memory tool with preloaded data so your client have to get data only during periodical reloads not all the time.
The best way is that your client will set reload once per night and make it incremental. If your tables have only new records load every night only records bigger than last primary key loaded.
If your tables have modified records you need to add in mysql last_modified_time field and maybe also set index on that field.
last_modified_time TIMESTAMP ON UPDATE CURRENT_TIMESTAMP
If your fields are get deleted the best is set it as deleted=1 in mysql otherwise your client will need to reload everything from that tables to get to know which rows were deleted.
Additionally your client to save resources should load only data in really simple style per table without JOINS:
SELECT [fields] FROM TABLE WHERE `id` > $(vLastId);
Qlikview is really good and fast for data modelling/joins so all data model your client can create in QLikview.
Reporting can indeed cause problems on a busy transactional database.
One approach you might want to examine is to have a replica (slave) of your database. MySQL supports this very well and your replica data can be as up to date as you require. You could then attach any reporting system to your replica to run heavy reports that won't affect your main database. This also gives you a backup (2nd copy) and the backup can further be used to create offline backups of your data also without affecting your main database.
There's lots of information on the setup of MySQL replicas so that's not too hard.
I hope that helps.
I am new to server side programming and am trying to understand relational databases a little better. Whenever I read about MYSQL vs SQLite people always talk about SQLite not being able to have multiple users. However, when I program with the Django Framework I am able to create multiple users on the sqlitedb. Can someone explain what people mean by multi-user? Thanks!
When people talk about multiple users in this context, they are talking about simultaneous connections to the database. The users in this case are threads in the web server that are accessing the database.
Different databases have different solutions for handling multiple connections working with the database at once. Generally reading is not a problem, as multiple reading operations can overlap without disturbing each other, but only one connection can write data in a specific unit at a a time.
The difference between concurrency for databases is basically how large units they lock when someone is writing. MySQL has an advanced system where records, blocks or tables can be locked depending on the need, while SQLite has a simpler system where it only locks the entire database.
The impact of this difference is seen when you have multiple threads in the webserver, where some threads want to read data and others want to write data. MySQL can read from one table and write into another at the same time without problem. SQLite has to suspend all incoming read requests whenever someone wants to write something, wait for all current reads to finish, do the write, and then open up for reading operations again.
As you can read here, sqlite supports multi users, but lock the whole db.
Sqlite is used for development ussualy, buy Mysql is a better sql for production, because it has a better support for concurrency access and write, but sqlite dont.
Hope helps
SQLite concurrency is explained in detail here.
In a nutshell, SQLite doesn't have the fine-grained concurrency mechanisms that MySQL does. When someone tries to write to a MySQL database, the MySQL database will only lock what it needs to lock, usually a single record, sometimes a table.
When a user writes to a SQLite database, the entire database file is momentarily locked. As you might imagine, this limits SQLite's ability to handle many concurrent users.
Multi-user means that many tasks (possibly on many separate computers) can have open connections to the database at the same time.
A multi-user database provides things like locks to allow these tasks to update the database safely.
Look at ScimoreDB. It's an embedded database that supports multi-process (or user) read and write access. It also can work as a client-server database.
I have a mysql database as my basic datastore for the master data. For complex multilevel queries similar to Friends of friends type i am having a graph datastore neo4j. Problem I am facing is while maintaining transactions, where i have to insert a user record in mysql and user node in neo4j. Now i want both of them to be successful. What i have accomplished is if neo4j insert is successful then I insert a mysql user record. but what if insert mysql user record fails i have an inconsistent state. Similar can happen if i insert mysql first and then neo4j. Is there any way i can accomplish transaction across mysql and neo4j. Would i need to maintain some kind of failed transaction log and execute them later?
Thanks! I know many wont agree with the combined approach for neo4j and mysql but i find this the best solution at the moment if i can pull away with consistent datastores.
Polyglot persistence (multi-database systems) is becoming commonplace, and this is a common challenge. You won't find any built-in mechanisms for transactions across disparate databases. Now: While there's no single "right answer" for your scenario, (and I'll do my best to keep my answer objective), think about your System of Record - which database holds the truth and needs to be correct? My guess is, it's the MySQL database.
So: Now you have your MySQL database, properly taken care of, saving content transactionally. Now there's your Neo4j database, which is being used for ancillary functions (searching for friends, in your case). Why not add your Neo4j graph nodes (and relationships) after the fact, as a separate operation? Will it really impact your system's operation if the insert into Neo4j is delayed? Is there anything detrimental to having an eventually-consistent update to your graph database? I suspect that, even with a follow-on operation, the delay will be minimal. That said: Only you know your app, and whether this synchronization between databases needs to be absolute.
I have a table in my database which contains all of the users for my application. Unfortunately, when I launched my application, I didn't think to include a column which tracked the time at which a particular user signed up, and now I wish I had (bad idea, yes indeed).
Is there, by any shred of luck, a way that MySQL tracks when a particular record is inserted (such as in record metadata???), and would allow me to grab it and insert in into a new dedicated column for this purpose?
I am running on a shared cPanel host, so I doubt I have access to the MySQL logs.
Thank you for your time.
Only if you have binary logging enabled will you be able to trace exact times for the transaction.
http://dev.mysql.com/doc/refman/5.5/en/binary-log.html
Its not just for replication, but also a form of transactional recording in case of emergency.
I have a MySQL DB which manages users’ accounts data.
Each user can only query he’s own data.
I have a script that on initial login gets the user data and inserts it to the DB.
I scheduled a cron process which updates all users’ data every 4 hours.
Here are my questions regarding it:
(1) - Do I need to implement some kind of lock mechanism on the initial login script?
This script can be executed by large number of users simultaneously - but every
user has a dedicated place in the DB so it does not affect other DB rows.
(2) - Same question on the cron process, should I handle this scenario:
While the cron process updates user i data, user i tries to fetch his data
from the DB.
I mean does MySQL already support and handles this scenario?
Any help would be appreciated.
Thanks.
No, you don't need to lock the database, MySQL engine handles this task for you. If you would make your database engine by yourself, you would have to be sure, that nothing will get in the way or conflict with data update, but since you are running such a smart thing as MySQL, you don't need to worry about it.
While data is updated, all queries will stand in line, until update finishes.