On Fri, 2007-05-18 at 11:46 -0700, Ken wrote: > Dan, > Can you explain to me how within the context of the test_server.c code > that the > sqlite3_enable_shared_Cache will improve concurrency, for a single DB > file access?
Others have pointed out in the past that in many cases using a shared-cache actually decreases concurrency. A smart embedded server (smarter than test_server.c) might be able to manage query execution to work around this. If the process does not require multiple logical connections, or saving memory and extra file-system reads is not an issue in your environment, shared-cache mode will likely do nothing for you. Dan. > I just don't see where any concurrency is gained. Sure maybe some > memory savings. But I must be brain dead, because I don't see how it > could improve concurrency given that a single thread is used to > perform db access. And all clients are queued and blocked upon the > single threads message queue. > > Thanks, > Ken > > > > > Dan Kennedy <[EMAIL PROTECTED]> wrote: > > Which in that case whats the point of a shared cache? > > What is it shared against, since all threads must send > > data to the shared server anyways and none may access > > it concurrently. > > The idea is to have a single cache shared accessed by > more than one logical connection (read: more than one > transaction context). It's meant to reduce IO and memory > usage in the case that a process opens more than one > connection to the same database file. > > It's quite a specialised feature. Only really useful > if you are implementing an embedded server. > > Dan > > > > > One thing that Other database engines do is allow read and > writes to occur without blocking. That is a Reader never > blocks a writer and a Writer never blocks a reader. SQLITE > does not do this, Only a single writer or Multiple readers, > but not both concurrently. > > > > I'm not trying to pick on sqlite, just pointing out that it > really doesn't perform multi threading or even conncurrent > access very well in a read/write environment. Read Only, its > great. Single threaded Read/Write ... Very good as well. > > > > Regards, > > Ken > > > > > > > > > > > > Doug Nebeker wrote: > > Yes I did the same experiment with > a lock that made thread A wait > > > > until B was finished. So actually only one thread can be > active at > > the time. > > > > I don't see how the outcome of this experiment can be of > any > > > > interest, as there is no time reduction any longer. But > your guess > > is > > > > right that, it works. > > > > > >How would multiple threads be faster than a single one when > you are > > accessing a single resource? > > > > Assumably the thread that is accessing the database either > spends some > > time gathering data to write > > or processing data it read. The single resource isn't in use > during > > that time. > > > > This email was sent to you by Reuters, the global news and > information company. > > To find out more about Reuters visit www.about.reuters.com > > > > Any views expressed in this message are those of the > individual sender, > > except where the sender specifically states them to be the > views of Reuters Limited. > > > > Reuters Limited is part of the Reuters Group of companies, > of which Reuters Group PLC is the ultimate parent company. > > Reuters Group PLC - Registered office address: The Reuters > Building, South Colonnade, Canary Wharf, London E14 5EP, > United Kingdom > > Registered No: 3296375 > > Registered in England and Wales > > > > > > > > > > ----------------------------------------------------------------------------- > > To unsubscribe, send email to > [EMAIL PROTECTED] > > > > ----------------------------------------------------------------------------- > > > > > > > > ----------------------------------------------------------------------------- > To unsubscribe, send email to > [EMAIL PROTECTED] > > ----------------------------------------------------------------------------- > > ----------------------------------------------------------------------------- To unsubscribe, send email to [EMAIL PROTECTED] -----------------------------------------------------------------------------
