HPL-2010-9 A survey of B-tree locking techniques - Graefe, Goetz Keyword(s): storage systems, databases, B-tree, indexes, concurrency control, locking Abstract: B-trees have been ubiquitous in database management systems for several decades, and they are used in other storage systems as well. Their basic structure and basic operations are well and widely understood including search, insertion, and deletion. Concurrency control of operations in B-trees, howe ... Full Report
Hi guys, I'm looking for some thoughts on this. I'm trying to do a clean 1 liner to substitute some values. What I have:
sed 's/Personid=.*/Personid=xxxxxx/' $tmpFileOut
sed 's/Person:.*/Person:xxxxxx/' $tmpFileOut
sed 's/PersonID:.*/PersonID: xxxxxx/' $tmpFileOut
Obviously that's a bit... (1 Reply)
If you have two or three minutes to spare, can you help with this ComputerWeekly survey? They are evaluating our site, asking a few questions like how often you visit the forums, what do you like the most, what can we improve, etc.
... (0 Replies)
Hello,
I'm a sysadmin in training and need to create/gather a survey from all the users about the servers that they use, problems, challenges etc.
Main purpose of the survey is to identify areas & room for improvement on the existing UNIX environment.
I have in mind these questions... (8 Replies)
Discussion started by: rahzzbietel
8 Replies
4. Post Here to Contact Site Administrators and Moderators
Hi guys!
I was wondering what the outcome was of your survey of a few months ago? One of the questions was if people were willing to pay for additional services like an own account, like username@unix.com with mail box, etc.
Sorry if I missed the results if you had already posted them.
Ivo (1 Reply)
dotlock(1) Mail Avenger 0.8.3 dotlock(1)NAME
dotlock - execute a command with a lock on a mailbox
SYNOPSIS
dotlock [-LPW] mbox-file command [arg ...]
DESCRIPTION
dotlock acquires a lock on the mailbox file mbox-file using both flock and a lock file, then executes command with any arguments specified.
When command exits, dotlock releases the lock.
dotlock attempts to clean up stale lockfiles. If it succeeds in locking an mbox-file with flock, and roughly 30 seconds elapse without
there being any changes to mbox-file or the lockfile, then dotlock will delete the lockfile and try again.
While it holds a lock, lockfile will keep updating the modification time of the lockfile every 15 seconds, to prevent the lock from getting
cleaned up in the event that command is slow.
OPTION
--noflock (-L)
Ordinarily, dotlock uses both flock and dotfile locking. (It uses flock first, but releases that lock in the even that dotfile locking
fails, so as to avoid deadlocking with applications that proceed in the reverse order.) The -L option disables flock locking, so that
dotlock only uses dotfile locking.
This is primarily useful as a wrapper around an application that already does flock locking, but to which you want to add dotfile
locking. (Even if your mail delivery system doesn't use flock, flock actually improves the efficiency of dotlock, so there is no
reason to disable it.)
--fcntl (-P)
This option enables fcntl (a.k.a. POSIX) file locking of mail spools, in addition to flock and dotfile locking. The advantage of fcntl
locking is that it may do the right thing over NFS. However, if either the NFS client or server does not properly support fcntl
locking, or if the file system is not mounted with the appropriate options, fcntl locking can fail in one of several ways. It can
allow different processes to lock the same file concurrently--even on the same machine. It can simply hang when trying to acquire a
lock, even if no other process holds a lock on the file. Also, on some OSes it can interact badly with flock locking, because those
OSes actually implement flock in terms of fcntl.
--nowait (-W)
With this option, dotlock simply exits non-zero and does not run command if it cannot immediately acquire the lock.
SEE ALSO avenger(1), deliver(1), avenger.local(8)
The Mail Avenger home page: <http://www.mailavenger.org/>.
BUGS
dotlock does not perform fcntl/lockf-style locking by default. Thus, if your mail reader exclusively uses fcntl for locking, there will be
race conditions unless you specify the --fcntl option.
flock does not work over network file systems. Thus, because of dotlock's mechanism for cleaning stale lock files, there is a possibility
that a network outage could lead to a race condition where the lockfile is cleared before command finishes executing. If lockfile detects
that the lock has been stolen, it prints a message to standard error, but does not do anything else (like try to kill command).
AUTHOR
David Mazieres
Mail Avenger 0.8.3 2012-04-05 dotlock(1)
