Re: lo function changed in PostgreSQL 8.1.1
От | Richard Huxton |
---|---|
Тема | Re: lo function changed in PostgreSQL 8.1.1 |
Дата | |
Msg-id | 439EBCE9.3090406@archonet.com обсуждение исходный текст |
Ответ на | lo function changed in PostgreSQL 8.1.1 ("Premsun Choltanwanich" <Premsun@nsasia.co.th>) |
Ответы |
Re: lo function changed in PostgreSQL 8.1.1
("Premsun Choltanwanich" <Premsun@nsasia.co.th>)
|
Список | pgsql-hackers |
Premsun Choltanwanich wrote: > Dear All, > > I use '$libdir/lo' for manage my Large Object for PostgreSQL 8.0.4 . Now > I try to up my PostgreSQL to new version as 8.1.1 but I think I got some > error about lo (Large Object). > > lo (Large Object) function that normally shown in function list now > disappear. I'm sure that I already check on Large Object box when I > install. I found some information on > http://www.postgresql.org/docs/8.1/interactive/lo-interfaces.html#AEN26978 about > lo function. PostgreSQL has many new lo function that I never use in > version 8.0.4 and some function I have use is not found (lo_in , lo_out). I don't see any major difference between the functions listed for the 8.0 and 8.1 manuals. Are you sure you're not talking about the contrib/lo type (see extract from the README.lo below)? If so, run the installer again and check you have ticked the box. HTH Overview One of the problems with the JDBC driver (and this affects the ODBC driver also), is that the specification assumes that references to BLOBS (Binary Large OBjectS) are stored within a table, and if that entry is changed, the associated BLOB is deleted from the database. As PostgreSQL stands, this doesn't occur. Large objects are treated as objects in their own right; a table entry can reference a large object by OID, but there can be multiple table entries referencing the same large object OID, so the system doesn't delete the large object just because you change or remove one such entry. Now this is fine for new PostgreSQL-specific applications, but existing ones using JDBC or ODBC won't delete the objects, resulting in orphaning - objects that are not referenced by anything, and simply occupy disk space. The Fix I've fixed this by creating a new data type 'lo', some support functions, and a Trigger which handles the orphaning problem. The trigger essentially just does a 'lo_unlink' whenever you delete or modify a value referencing a large object. When you use this trigger, you are assuming that there is only one database reference to any large object that is referenced in a trigger-controlled column! The 'lo' type was created because we needed to differentiate between plain OIDs and Large Objects. Currently the JDBC driver handles this dilemma easily, but (after talking to Byron), the ODBC driver needed a unique type. They had created an 'lo' type, but not the solution to orphaning. You don't actually have to use the 'lo' type to use the trigger, but it may be convenient to use it to keep track of which columns in your database represent large objects that you are managing with the trigger. -- Richard Huxton Archonet Ltd
В списке pgsql-hackers по дате отправления:
Следующее
От: "Malcus"Дата:
Сообщение: ERROR: could not access status of transaction on postgresql 8.0.3