Published on December 23rd, 2020 | by Sunit Nandi0
Top 3 issues with concurrent requests on a SQL server
SQL databases are built to handle a whole heap of processes at the same time, allowing them to keep apps and websites running smoothly and enabling them to accommodate all sorts of workloads besides.
However, concurrency like this can have its issues, and if problems do arise then a spot of troubleshooting will be necessary.
To help you monitor and maintain a SQL server more effectively, here are just three of the most common complications that arise as a result of concurrent requests.
Arguably the most oft-discussed issue to arise in SQL environments, blocking comes about because of the way that different lock modes are assigned to processes.
For example, if a process has an exclusive lock on a particular resource then it will be given priority over a concurrent request which does not have the same privileges. In this case the latter process will be forced to wait until the request is completed and lock is released.
Blocking of this kind is not only entirely normal within SQL servers, but also essential to the way they operate. It prevents multiple requests from attempting to alter the same data at the same time, thus preserving the integrity of all the information and avoiding chaos and corruption.
Of course there are problematic types of blocking which do need to be looked into, and server monitoring tools will be able to detect these and provide alerts as and when they arise. You can manually seek them out by scrutinizing wait stats, but this is a more time consuming approach to troubleshooting SQL blocking.
Deadlocks are a more severe side effect of the way that a SQL server handles concurrent requests, and again they are important for the purposes of preserving data integrity, but may necessitate proactive intervention from DBAs.
Deadlocking is the result of two or more processes possessing an exclusive lock on a server resource and needing to make the leap to another resource already occupied by a process with its own exclusive lock. The result is that these processes cannot switch places cleanly and thus are at loggerheads with one another in a potentially perpetual stalemate.
The good news is that the server will not allow a deadlock to last indefinitely, but will rather intervene and terminate one of the processes to get the cogs moving again. This of course leaves a process as the victim, with an error logged so that it can be identified with ease and rerun if necessary.
Again, deadlocking is not always a problem and if it only happens in rare, infrequent circumstances then it need not be too concerning. However, analyzing and tracking the instances of deadlocks arising is sensible so that you can be on the lookout for those that do need fixing.
The ultimate upshot of any SQL server concurrency conundrum is that performance will suffer, and while this is all in the aid of ensuring that the data is accurate and consistent across the board, it is obviously sub-optimal for a database to be running at a snail’s pace.
Performance problems can arise from a combination of different concurrency issues, including the locking, blocking and deadlocking covered above. It is also worth noting that these are not the only elements to check when troubleshooting, as hardware faults and bottlenecks are also worth looking into, along with the use of storage in TempDB.
Monitoring a server and fixing issues when they crop up, rather than letting them linger unaddressed, is always the best route for any administrator worth their salt.