Re: SMSI: databases corrupted on crash and permission issueson OSX
This WebDNA talk-list message is from 2002
It keeps the original formatting.
numero = 43620
interpreted = N
texte = Dale LaFountain wrote: > In the meantime I have to ask: why doesn't webcat write databases to a > temp file (i.e. .orders.db.tmp) before replacing the original file? If > coded robustly, this change should virtually eliminate the possibility > of truncating db files. > The most robust way to do this (assuming that WebCat has the file still open) is to write to a temp file in the same directory, then atomically rename the temp file to the original file name, then close and reopen the file. The key here is that as long as the file is open, the rename doesn't affect the running process (since it already has a filehandle to the old file, regardless of it's current name).The close/open then immediately has access to the original filename with the new contents. The filesystem does not recover the old file until after all applications with an active handle close the file, so it is a very clean way to manage it. It even works with multiple threads, since only the threads with the file already open have the old file and as soon as they close it, they get the new data on next open().John -- John Peacock Director of Information Research and Technology Rowman & Littlefield Publishing Group 4720 Boston Way Lanham, MD 20706 301-459-3366 x.5010 fax 301-429-5747 ------------------------------------------------------------- This message is sent to you because you are subscribed to the mailing list
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Dale LaFountain wrote: > In the meantime I have to ask: why doesn't webcat write databases to a > temp file (i.e. .orders.db.tmp) before replacing the original file? If > coded robustly, this change should virtually eliminate the possibility > of truncating db files. > The most robust way to do this (assuming that WebCat has the file still open) is to write to a temp file in the same directory, then atomically rename the temp file to the original file name, then close and reopen the file. The key here is that as long as the file is open, the rename doesn't affect the running process (since it already has a filehandle to the old file, regardless of it's current name).The close/open then immediately has access to the original filename with the new contents. The filesystem does not recover the old file until after all applications with an active handle close the file, so it is a very clean way to manage it. It even works with multiple threads, since only the threads with the file already open have the old file and as soon as they close it, they get the new data on next open().John -- John Peacock Director of Information Research and Technology Rowman & Littlefield Publishing Group 4720 Boston Way Lanham, MD 20706 301-459-3366 x.5010 fax 301-429-5747 ------------------------------------------------------------- This message is sent to you because you are subscribed to the mailing list . To unsubscribe, E-mail to: To switch to the DIGEST mode, E-mail to Web Archive of this list is at: http://search.smithmicro.com/
John Peacock
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