A Primer on Concurrency Issues
Problems of concurrency happen when multiple application processes modify and use the same resource at the same time, or concurrently. Process state mutates unexpectedly, leading to double processing and other issues. Problems tend to occur when the resource is being accessed within a short timespan, as shown in the following diagram, but it can also happen over a longer period.
Technically, concurrency issues aren’t constrained to the database layer, but they most often occur there because the database is the typically the most shared resource.
Although we treat concurrency and parallelism as synonyms in this chapter, ...