Patrick Dung wrote: > As I have seen, some database created or pre-allocate large physical files on the file system to as > the backend of the database tablespace. > > For Postgresql, I have observed that it created several files in the base and global directory. > > It may be by design, what is the pros and cons of this behavior? You are a bit unspecific; are you talking about Oracle? The disk layout is of course by design. Oracle uses large container files and keeps its data in those. As far as I know, this is to bypass file system functionality. Oracle usually recommends direct I/O and bypasses file system functionality (caching etc.) as much as possible. I guess one reason for this is that, historically, file system implementations incurred more overhead than they do now and had all sorts of other problems with larger amounts of data. These days, filesystems perform much better, so this is no longer necessary, but Oracle is quite old software. Another reason may be Oracle's quest to rule the world, and the storage layer is part of that. Lately, Oracle tries to get everybody to use ASM, their storage layer, which completely bypasses file system functionality. PostgreSQL, on the other hand, does not have the resources or intentions to write a better file system and actually uses file system capabilities like caching to improve performance. PostgreSQL keeps what Oracle calls segments as individual files in a directory structure. Yours, Laurenz Albe -- Sent via pgsql-general mailing list (pgsql-general@xxxxxxxxxxxxxx) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-general
