ver. Venus then notifies the AVSG that one (or more) of its members have stale data. The preferred server then initiates a callback. A callback is a promise made by the server that it will notify the client before allowing any other client to modify the data. When Venus locates the file it responds to the kernel, which then returns the calling program from the system call. The first time the kernel passes on an open request for a file Venus will get the entire file from the server using remote procedure calls. The file is then stored in the cache area as a container file. It is now an ordinary file on the local disk and read-write operations are almost entirely handled by the local file system. Venus caches all the directory files and attributes. Venus allows operations on the file to proceed without contacting the servers as long as the requested files are present in the cache. When a file is modified and closed Venus updates the AVSG by sending them the new file through parallel remote procedure calls. Removal of or addition of files and symbolic links is also sent to the AVSG. This is one area where updating conflicts could arise. CODA uses an optimistic strategy to deal with these conflicts, which we will discuss later.Disconnected OperationCODA allows for transparent disconnected operation. It achieves this through a three-phase process: hoarding, server emulation and reintegration. The hoarding phase occurs before disconnection and is actually a cache management phase. Hoarding attempts to capture immediate and future working-sets. Server emulation occurs during disconnection, it is where a pseudo-server emulates the semantic and security checks made by the real servers. It also keeps a detailed record of its actions in order to make the third phase quicker and more efficient. Reintegration is where the pseudo-server gets back up to date with the real servers. This includes conflict detection, automatic resolu...
