The decision of how often to run checkpoints may therefore vary from one application to another depending on the relative read and write performance requirements of the application. The checkpoint remembers in the wal-index how far it got and will resume transferring content from the WAL to the database from where it left off on the next invocation.
Let's introduce a page identifier. For the sake of simplicity in this article, every cache group is named as a cache.
Specialized applications for which the default implementation of shared memory is unacceptable can devise alternative methods via a custom VFS. The checkpointer makes an effort to do as many sequential page writes to the database as it can the pages are transferred from WAL to database in ascending order but even then there will typically be many seek operations interspersed among the page writes.
It is not possible to open read-only WAL databases.
In addition each of your job duties should be specific and listed by decreasing importance. This scenario can be avoided by ensuring that there are "reader gaps": times when no processes are reading from the database and that checkpoints are attempted during those times.