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Purchase This document was originally created in early when SQLite version 2 was still in widespread use and was written to introduce the new concepts of SQLite version 3 to readers who were already familiar with SQLite version 2. But these days, most readers of this document have probably never seen SQLite version 2 and are only familiar with SQLite version 3.
Nevertheless, this document continues to serve as an authoritative reference to how database file locking works in SQLite version 3. The document only describes locking for the older rollback-mode transaction mechanism.
Locking for the newer write-ahead log or WAL mode is described separately. The new mechanism also allows atomic commits of transactions involving multiple database files.
This document describes the new locking mechanism. The pager module makes sure changes happen all at once, that either all changes occur or none of them do, that two or more processes do not try to access the database in incompatible ways at the same time, and that once changes have been written they persist until explicitly deleted.
The pager also provides a memory cache of some of the contents of the disk file. The pager is unconcerned with the details of B-Trees, text encodings, indices, and so forth. From the point of view of the pager the database consists of a single file of uniform-sized blocks.
Each block is called a "page" and is usually bytes in size. The pages are numbered beginning with 1. So the first bytes of the database are called "page 1" and the second bytes are call "page 2" and so forth. All other encoding details are handled by higher layers of the library.
The pager communicates with the operating system using one of several modules Examples: The pager module effectively controls access for separate threads, or separate processes, or both. Throughout this document whenever the word "process" is written you may substitute the word "thread" without changing the truth of the statement.
The database may be neither read nor written. Any internally cached data is considered suspect and subject to verification against the database file before being used. Other processes can read or write the database as their own locking states permit.
This is the default state. The operating system interface layer understands and tracks all five locking states described above.
The pager module only tracks four of the five locking states. The rollback journal is an ordinary disk file that is always located in the same directory or folder as the database file and has the same name as the database file with the addition of a -journal suffix. The rollback journal also records the initial size of the database so that if the database file grows it can be truncated back to its original size on a rollback.
But there is also a separate aggregate journal called the master journal. The master journal does not contain page data used for rolling back changes. Instead the master journal contains the names of the individual database rollback journals for each of the ATTACHed databases.
Each of the individual database rollback journals also contain the name of the master journal. If there are no ATTACHed databases or if none of the ATTACHed database is participating in the current transaction no master journal is created and the normal rollback journal contains an empty string in the place normally reserved for recording the name of the master journal.
A rollback journal is said to be hot if it needs to be rolled back in order to restore the integrity of its database. A hot journal is created when a process is in the middle of a database update and a program or operating system crash or power failure prevents the update from completing.
Hot journals are an exception condition. Hot journals exist to recover from crashes and power failures. If everything is working correctly that is, if there are no crashes or power failures you will never get a hot journal. If no master journal is involved, then a journal is hot if it exists and has a non-zero header and its corresponding database file does not have a RESERVED lock.Here, we see another drawback.
To function properly, NFS basically requires you to have the same UID/GID on all machines. The files you want to access belong to and have permissions You're user on the client has uid= The GIDs don't match either, so .
Now both you and usera have complete access to the NFS share.
I have used the setgid bit, so you may have to enable it, I don't remember it. Add any users you wish to have access to this directory to the usera group. Now both you and usera have complete access to the NFS share. I have used the setgid bit, so you may have to enable it, I don't remember it. Add any users you .
Update (Nov 9, ): As noted in the comments below, Windows Services for UNIX Version (SFU) is no longer supported on Windows 7 and For these versions, try installing Cygwin with the optional nfs-server component.
Mar 15, · The default policy is set to NATIVE, which means that Active Directory controls access to the file from the CIFS side, and NFS controls access from the NFS side. If a user has write permissions in CIFS but not in NFS, he can only write .
windows nfs client write access. I've got a problem with the Windows UNIX Services. i know it has been a long time since this post but would mind explaining how you added the linux user id to the windows user.
i can mount a unix nfs to windows but i cannot write to the unix nfs share and i think this might help caninariojana.coms: 5.