my website-hoster is allowing me unlimited amount of MS SQL databases - but each database may only be a max of 3GB.
My Users database is separate from my Main database. The Main db contains several tables consisting of strings and numbers (no blobs), for example: "Messages", "BugReports", "UserOptions"
I am allowing offline messages between users - when a message can't be delivered it is stored in the "Messages" table. This works great, but I worry: in the long term, what happens when the website gets a lot of traffic and the database nears 3GB ?
Should I make the "Messages" and "BugReports" tables separate databases instead ?
If you store them in a separate database, they will still fill that one up, wouldn't they? So you'll need to shard the Messages table across a number of databases.
If you 're site is so successful to get enough traffic that you run into the 3Gb limit, then look at changing the provider to someone that allows bigger databases, or a dedicated host, or collocation. Yes, you can argue that if you make your app work on 3 GB shards you can scale easier later, but you'll spend a lot of effort to get this working to surpass such an artificial limit. Spend you effort on features useful to your end users instead. With a good design, 3Gb should go a long mile.
Host MyPhpAdmin on ur server. I'm not sure who your hosting with but a lot of them offer unlimites disk space. That way you will have unlimited databases with unlimited capacity.
Related
I have a queer situation. I am managing an e-commerce site built on Django with Postgresql. It has two versions - English and Japanese. Because of a release that has brought a huge number of users, the site (specifically Postgres) is overloaded and crashing. The only safe solution which I can think of is to put these two separately on two separate servers so that En and Jp traffic gets their own dedicated server. Now, the new server is ready but during the time of domain propagation, and during half-propagated stages (new one being seen from some countries and old one from some) there will be transactions on both. Users are buying digital stuff in hundreds of numbers every minute. So, there is no way to turn the server off for a turnover.
Is there a way to sync the two databases at a later stage (because if both share a database, the new server will be pointless). The bottleneck is Postgres, and has already been tuned for maximum possible connections on this server, and kernel.shmmax is at its limit. DB pooling also will need time to setup and some downtime as well, which am not permitted to do at the moment. What I mean by sync is that once full propagation occurs, I wish to unify the DB dump files from both and make one which has all records of both synced in time. The structure is rather complex so many tables will need sync. Is this do-able ..?
Thanks in advance !
I am working on Asp.Net MVC web application, back-end is SQL Server 2012.
This application will provide billing, accounting, and inventory management. The user will create an account by signup. just like http://www.quickbooks.in. Each user will create some masters and various transactions. There is no limit, user can make unlimited records in the database.
I want to keep stable database performance, after heavy data load. I am maintaining proper indexing and primary keys in it, but there would be a heavy load on the database, per user.
So, should I create a separate database for each user, or should maintain one database with UserID. Add UserID in each table and making a partition based on UserID?
I am not an expert in SQL Server, so please provide suggestions with clear specifications.
Please inform me if there is any lack of information.
A DB per user is what happens when customers need to be able pack up and leave taking the actual database with them. Think of a self hosted wordpress website. Or if there are incredible risks to one user accidentally seeing another user's data, so it's safer to rely on the servers security model than to rely on remembering to add the UserId filter to all your queries. I can't imagine a scenario like that, but who knows-- maybe if the privacy laws allowed for jail time, I would rather data partitioned by security rules rather than carefully writing WHERE clauses.
If you did do user-per-database, creating a new user will be 10x more effort. While INSERT, UPDATE and so on stay the same from version to version, with each upgrade the syntax for database, user creation, permission granting and so on will evolve enough to break those scripts each SQL version upgrade.
Also, this will multiply your migration headaches by the number of users. Let's say you have 5000 users and you need to add some new columns, change a columns data type, update a trigger, and so on. Instead of needing to run that change script 1x, you need to run it 5000 times.
Per user Dbs also probably wastes disk space. Each of those databases is going to have a transaction log, sitting idle taking up the minimum log space.
As for load, if collectively your 5000 users are doing 1 billion inserts, updates and so on per day, my intuition tells me that it's going to be faster on one database, unless there is some sort of contension issue (everyone reading and writing to the same table at the same time and the same pages of the same table). Each database has machine resources (probably threads and memory) per database doing housekeeping, so these extra DBs can't be free.
Anyhow, the best thing to do is to simulate the two architectures and use a random data generator to simulate load and see how they perform.
It's not an easy answer to give.
First, there is logical design to be considered. Then you have integrity, security, management and performance (in this very order).
A database is a logical unit of data, self contained. Ideally, you should be able to take a database, move it to another instance, probably change the connection strings and be running again.
All the constraints are database-level. No foreign keys can exist referencing some object outside the database.
So, try thinking in these terms first.
How would you reliably prevent one user messing up the other user's data? Keep in mind that it's just a matter of time before someone opens an excel sheet and fire up queries on the database bypassing your application. Row level security in SQL Server is something you don't want to deal with.
Multiple databases mean that all management tasks should be scripted out and executed on all databases. Yes, there is some overhead to it, but once you set it up it's just the matter of monitoring. If a database goes suspect, it's a single customer down, not all of them. You can even have different versions for different customes if each customer have it's own database. Additionally, if you roll an upgrade, you can do it per customer, so the inpact will be much less.
Performance is the least relevant factor here. Of course, it really depends on how many customers and how much data, but proper indexing will solve these issues. Scale-out is much easier with multiple databases.
BTW, partitioning, as you mentioned it, is never a performance booster, it's simply a management feature, allowing for faster loading and evicting of data from a table.
I'd probably put each customer in separate database, but it's up to you eventually to make a decision for yourself. Hope I've helped some with this.
We have data stored in a data warehouse as follows:
Price
Date
Product Name (varchar(25))
We currently only have four products. That changes very infrequently (on average once every 10 years). Once every business day, four new data points are added representing the day's price for each product.
On the website, a user can request this information by entering a date range and selecting one or more products names. Analytics shows that the feature is not heavily used (about 10 users requests per week).
It was suggested that the data warehouse should daily push (SFTP) a CSV file containing all data (currently 6718 rows of this data and growing by four each day) to the web server. Then, the web server would read data from the file and display that data whenever a user made a request.
Usually, the push would only be once a day, but more than one push could be possible to communicate (infrequent) price corrections. Even in the price correction scenario, all data would be delivered in the file. What are problems with this approach?
Would it be better to have the web server make a request to the data warehouse per user request? Or does this have issues such as a greater chance for network errors or performance issues?
Would it be better to have the web server make a request to the data warehouse per user request?
Yes it would. You have very little data, so there is no need to try and 'cache' this in some way. (Apart from the fact that CSV might not be the best way to do this).
There is nothing stopping you from doing these requests from the webserver to the database server. With as little information as this you will not find performance an issue, but even if it would be when everything grows, there is a lot to be gained on the database-side (indexes etc) that will help you survive the next 100 years in this fashion.
The amount of requests from your users (also extremely small) does not need any special treatment, so again, direct query would be the best.
Or does this have issues such as a greater chance for network errors or performance issues?
Well, it might, but that would not justify your CSV method. Examples and why you need not worry, could be
the connection with the databaseserver is down.
This is an issue for both methods, but with only one connection per day the change of a 1-in-10000 failures might seem to be better for once-a-day methods. But these issues should not come up very often, and if they do, you should be able to handle them. (retry request, give a message to user). This is what enourmous amounts of websites do, so trust me if I say that this will not be an issue. Also, think of what it would mean if your daily update failed? That would present a bigger problem!
Performance issues
as said, this is due to the amount of data and requests, not a problem. And even if it becomes one, this is a problem you should be able to catch at a different level. Use a caching system (non CSV) on the database server. Use a caching system on the webserver. Fix your indexes to stop performance from being a problem.
BUT:
It is far from strange to want your data-warehouse separated from your web system. If this is a requirement, and it surely could be, the best thing you can do is re-create your warehouse-database (the one I just defended as being good enough to query directly) on another machine. You might get good results by doing a master-slave system
your datawarehouse is a master-database: it sends all changes to the slave but is inexcessible otherwise
your 2nd database (on your webserver even) gets all updates from the master, and is read-only. you can only query it for data
your webserver cannot connect to the datawarehouse, but can connect to your slave to read information. Even if there was an injection hack, it doesn't matter, as it is read-only.
Now you don't have a single moment where you update the queried database (the master-slave replication will keep it updated always), but no chance that the queries from the webserver put your warehouse in danger. profit!
I don't really see how SQL injection could be a real concern. I assume you have some calendar type field that the user fills in to get data out. If this is the only form just ensure that the only field that is in it is a date then something like DROP TABLE isn't possible. As for getting access to the database, that is another issue. However, a separate file with just the connection function should do fine in most cases so that a user can't, say open your webpage in an HTML viewer and see your database connection string.
As for the CSV, I would have to say querying a database per user, especially if it's only used ~10 times weekly would be much more efficient than the CSV. I just equate the CSV as overkill because again you only have ~10 users attempting to get some information, to export an updated CSV every day would be too much for such little pay off.
EDIT:
Also if an attack is a big concern, which that really depends on the nature of the business, the data being stored, and the visitors you receive, you could always create a backup as another option. I don't really see a reason for this as your question is currently stated, but it is a possibility that even with the best security an attack could happen. That mainly just depends on if the attackers want the information you have.
I searched online for awhile about what is "Excessive resource usage" on SQL Azure, still cannot get an idea.
Some articles suggest query takes too long, too much memory etc will cause "Excessive resource usage". But If I use simple query, simple data structure, what will happen?
For example: I get a 1G SQL Azure as session state. Since session is a very small string, and save/delete all the time, I don't think it will grow to 1G for millions of session simultaneously. You can calculate, for 1 million session, 20 char each, only take 20M space, consider 20 minutes expire etc. Cannot even close to 1G. But the queries, should be lots and lots. Each query will be very simple and fast by index.
I wanna know, if this use will be consider as "Excessive resource usage"? Is there any hard number to limit you on the usage?
Btw, as example above, if all happen in same datacenter, so all cost is 1G database which is $10 a month, right?
Unfortunately the answer is 'it depends'. I think that probably the best reference (with guidance) on the SQL Azure Query Throttle is here: TechNet Article on SQL Azure Perormance This will povide details about the metrics that are monitored and the mechanism of the throttle.
The reason that I say it depends is that the throttle is non-deterministic for any given user. This is because the throttle will be activated based on the total load on the node (physical SQL Server in Azure DC). While the subscribers who will get throttled are the subscribers delivering the greatest load the level at which the throttle kicks in will depend on the total load on the node. SO if you are on a quiet node (where other tenant DBs are relatively inactive) then you will be able to put through a bunch more throughput than if you are on a busy node.
It is very appealing to use 1GB SQL Azure DBs for session state storage; you've identified the cost benefits. You are taking a risk though. One way to mitigate this risk is to partition across at least two SQL Azure 1GB DBs and adjust the load yourself based on whether one of the DBs starts hitting the throttle.
Another option if you want determinism for throughput is to use the WIndows Azure Cache to back your sesion state store. The Cache has hard pre-defined limits for query throughput so you can plan for it more easily Azure Caching FAQ including Limits. The Cache approach is probably a bit more expensive but with a lower risk of problems.
Our database architecture consists of two Sql Server 2005 servers each with an instance of the same database structure: one for all reads, and one for all writes. We use transactional replication to keep the read database up-to-date.
The two servers are very high-spec indeed (the write server has 32GB of RAM), and are connected via a fibre network.
When deciding upon this architecture we were led to believe that the latency for data to be replicated to the read server would be in the order of a few milliseconds (depending on load, obviously). In practice we are seeing latency of around 2-5 seconds in even the simplest of cases, which is unsatisfactory. By a simplest case, I mean updating a single value in a single row in a single table on the write db and seeing how long it takes to observe the new value in the read database.
What factors should we be looking at to achieve latency below 1 second? Is this even achievable?
Alternatively, is there a different mode of replication we should consider? What is the best practice for the locations of the data and log files?
Edit
Thanks to all for the advice and insight - I believe that the latency periods we are experiencing are normal; we were mis-led by our db hosting company as to what latency times to expect!
We're using the technique described near the bottom of this MSDN article (under the heading "scaling databases"), and we'd failed to deal properly with this warning:
The consequence of creating such specialized databases is latency: a write is now going to take time to be distributed to the reader databases. But if you can deal with the latency, the scaling potential is huge.
We're now looking at implementing a change to our caching mechanism that enforces reads from the write database when an item of data is considered to be "volatile".
No. It's highly unlikely you could achieve sub-1s latency times with SQL Server transactional replication even with fast hardware.
If you can get 1 - 5 seconds latency then you are doing well.
From here:
Using transactional replication, it is
possible for a Subscriber to be a few
seconds behind the Publisher. With a
latency of only a few seconds, the
Subscriber can easily be used as a
reporting server, offloading expensive
user queries and reporting from the
Publisher to the Subscriber.
In the following scenario (using the
Customer table shown later in this
section) the Subscriber was only four
seconds behind the Publisher. Even
more impressive, 60 percent of the
time it had a latency of two seconds
or less. The time is measured from
when the record was inserted or
updated at the Publisher until it was
actually written to the subscribing
database.
I would say it's definately possible.
I would look at:
Your network
Run ping commands between the two servers and see if there are any issues
If the servers are next to each other you should have < 1 ms.
Bottlenecks on the server
This could be network traffic (volume)
Like network cards not being configured for 1GB/sec
Anti-virus or other things
Do some analysis on some queries and see if you can identify indexes or locking which might be a problem
See if any of the selects on the read database might be blocking the writes.
Add with (nolock), and see if this makes a difference on one or two queries you're analyzing.
Essentially you have a complicated system which you have a problem with, you need to determine which component is the problem and fix it.
Transactional replication is probably best if the reports / selects you need to run need to be up to date. If they don't you could look at log shipping, although that would add some down time with each import.
For data/log files, make sure they're on seperate drives so the performance is maximized.
Something to remember about transaction replication is that a single update now requires several operations to happen for that change to occur.
First you update the source table.
Next the log readers sees the change and writes the change to the distribution database.
Next the distribution agent sees the new entry in the distribution database and reads that change, then runs the correct stored procedure on the subscriber to update the row.
If you monitor the statement run times on the two servers you'll probably see that they are running in just a few milliseconds. However it is the lag time while waiting for the log reader and distribution agent to see that they need to do something which is going to kill you.
If you truly need sub second processing time then you will want to look into writing your own processing engine to handle data moving from one server to another. I would recommend using SQL Service Broker to handle this as this way everything is native to SQL Server and no third party code has to be written.