If you use serializable transactions then you effectively single thread access to everything, which is HORRIBLE for performance because your concurrency goes basically to one. So using serializable transactions as the default is almost never a good idea.
I believe you're correct that a serializable transaction would make it safe, but the loss of concurrency is a steep price to pay when a unique index will assure it for no performance penalty (and probably actually make queries faster, since uniqueness is a good indicator of a field to be used in a WHERE clause). cheers, barneyb On Feb 11, 2008 4:43 PM, s. isaac dealey <[EMAIL PROTECTED]> wrote: > > The transaction won't actually isolate you from a race condition. > > Other connections will be able to insert at the same time. A full > > table lock, on the other hand, will protect you. A unique key > > constraint would also do it. > > Umm... I was under the impression that a serializable transaction lock > would lock the table. If you omit the isolation, the database may not > necessarily serialize it -- but the whole point of the serializeable > isolation *is* to single-thread access to those resources for the > purpose of eliminating race conditions. Docs seem to confirm that notion - > this is from the CF7 docs for cftransaction: > > * serializable: places an exclusive lock on every data table in use for > the duration of the transaction. Causes access to the database to be > single-threaded and is therefore not recommended for normal database > access. > > http://livedocs.adobe.com/coldfusion/7/htmldocs/00000346.htm > > Thing is, I believe according to standard serializable is supposed to be > the default (I'm actually not certain of that, but remember Jochem > saying something about it)... however, because databases are notorious > for being iffy on standards support, etc. it's generally better to > explicitly declare the isolation in the cftransaction tag, since the > docs say it'll use whatever the default is for the associated database > if you omit it. May be okay to omit if you know for example that your > company always uses a specific db platform configured a particular way > and therefore always means a default isolation of x, but for me, that's > still an area where I'd rather just specify it in the tag. > > This from a guy who likes to use a tool to generate his forms that > eliminates the need to specify value attributes. :P > > -- > s. isaac dealey ^ new epoch > isn't it time for a change? > ph: 503.236.3691 > > http://onTap.riaforge.org/blog > > > > ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~| Adobe® ColdFusion® 8 software 8 is the most important and dramatic release to date Get the Free Trial http://ad.doubleclick.net/clk;160198600;22374440;w Archive: http://www.houseoffusion.com/groups/CF-Talk/message.cfm/messageid:298761 Subscription: http://www.houseoffusion.com/groups/CF-Talk/subscribe.cfm Unsubscribe: http://www.houseoffusion.com/cf_lists/unsubscribe.cfm?user=89.70.4
