The unix mv command does not affect currently open file handles, only the
directory entry or entries (atomically, unless it is a cross-filesystem mv,
which is accomplished by pretrending you said cp and is in no way atomic).
As long as the first command shell is running, it will continue to see (and
modify) the original contents. A new command shell would open a different file
(the one the directory entry now points to) and therefore operate on a
different file than the first command shell.
A "file" on unix consists of an "inode" (the basic file system entity that
allows allocation of disk space) and at least one "directory entry" (that
assigns a name to an inode). An inode is freed when the last directory entry
referring to it is removed and the last file handle referencing it is closed.
e.g.
x) run sqlite on a.db (let's assume this file is inode number 4711)
x) mv a.db b.db (now the directory entry for b.db points to inode 4711)
x) mv x.db a.db (now the directory entry for a.db points to the inode of x.db,
let's assume this is 815)
x) run sqlite on a.db (this opens inode 815)
note: to access the former a.db you now have to use the name b.db
e.g.
x) run sqlite on a.db (again assumed inode number 4711)
x) mv b.db a.db (now the directory entry for a.db points to the inode of b.db,
again assumed 815)
x) run sqlite on a.db (this opens inode 815)
note: the former contents of a.db (inode 4711) is now no longer referenced by
any directory entry. It will continue to stick around until the (last) file
handle is closed, after which it will be deleted.
In both cases, the two instances of sqlite are operating on different inodes
i.e. file contents and therefore cannot see each others' changes.
-Ursprüngliche Nachricht-
Von: sqlite-users [mailto:sqlite-users-boun...@mailinglists.sqlite.org] Im
Auftrag von Roman Fleysher
Gesendet: Donnerstag, 16. Februar 2017 06:52
An: SQLite mailing list
Betreff: Re: [sqlite] 3.17.0 does not read updated DB
My mistake: I do not update DB. I rename (unix mv) the DB.
Roman
From: sqlite-users [sqlite-users-boun...@mailinglists.sqlite.org] on behalf of
Roman Fleysher [roman.fleys...@einstein.yu.edu]
Sent: Thursday, February 16, 2017 12:33 AM
To: General Discussion of SQLite Database
Subject: [sqlite] 3.17.0 does not read updated DB
Dear SQLiters,
Is it possible that sqlite3 version 3.17.0 (command shell) does not pick up
updated content of a DB file? I updated DB while it was attached in sqlite3 and
SELECT did not produce new results. Instead it printed the same output as
before DB file was updated.
Update was performed using sqlite3 version 3.8.11 (also command shell). I seem
to be able to replicate that.
Roman
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