Обсуждение: Abort transaction on duplicate key error
Hi all, Sorry for bothering you with my stuff for the second time but I haven't got any answer within two days and the problem appears fundamental, at least to me. I have a C application running to deal with meteorological data like temperature, precipitation, wind speed, wind direction, ... And I mean loads of data like several thousand sets within every ten minutes. From time to time it happens the transmitters have delivered wrong data, so they send the sets again to be taken as correction. The idea is to create a unique index on the timestamp, the location id and the measurement id, then when receiving a duplicate key error move on to an update command on that specific row. But, within PostgreSQL this strategy does not work any longer within a chained transaction, because the duplicate key error leads to 'abort the whole transaction'. What I can do is change from chained transaction to unchained transaction, but what I have read in the mailing list so far, the commit operation requires loads of cpu time, and I do not have time for this when processing thousands of sets. I am wondering now whether there is a fundamental design error in my strategy. Any ideas, suggestions highly appreciated and thanks for reading so far. Regards, Christoph My first message: In a C application I want to run several insert commands within a chained transaction (for faster execution). From time to time there will be an insert command causing an ERROR: Cannot insert a duplicate key into a unique index As a result, the whole transaction is aborted and all the previous inserts are lost. Is there any way to preserve the data except working with "autocommit" ? What I have in mind particularly is something like "Do not abort on duplicate key error".
Haller Christoph wrote: > My first message: > In a C application I want to run several > insert commands within a chained transaction > (for faster execution). > >From time to time there will be an insert command > causing an > ERROR: Cannot insert a duplicate key into a unique index > > As a result, the whole transaction is aborted and all > the previous inserts are lost. > Is there any way to preserve the data > except working with "autocommit" ? > What I have in mind particularly is something like > "Do not abort on duplicate key error". Simply select by the key you want to enter. If you get 100 an insert is ok, otherwise do an update. Oracle has a feature called 'insert or update' which follows this strategy. There also was some talk on this list about implementing this, but I don't remember the conclusion. BTW: I strongly recommend staying away from autocommit. You cannot control/know whether/when you started a new transaction. Christof PS: I would love to have nested transactions, too. But no time to spare ... Perhaps somebody does this for 7.3?
Thanks a lot. Now that I've read your message, I wonder why I was asking something trivial. Christoph > > In a C application I want to run several > > insert commands within a chained transaction > > (for faster execution). > > >From time to time there will be an insert command > > causing an > > ERROR: Cannot insert a duplicate key into a unique index > > > > As a result, the whole transaction is aborted and all > > the previous inserts are lost. > > Is there any way to preserve the data > > except working with "autocommit" ? > > What I have in mind particularly is something like > > "Do not abort on duplicate key error". > > Simply select by the key you want to enter. If you get 100 an insert is ok, > otherwise do an update. Oracle has a feature called 'insert or update' which > follows this strategy. There also was some talk on this list about > implementing this, but I don't remember the conclusion. > > BTW: I strongly recommend staying away from autocommit. You cannot > control/know whether/when you started a new transaction. > > Christof > > PS: I would love to have nested transactions, too. But no time to spare ... > Perhaps somebody does this for 7.3? >
Haller, The way I have handled this in the past is to attempt the following insert, followed by an update if the insert doesn't insert any rows: insert into foo (fooPK, foo2) select 'valuePK', 'value2' where not exists (select 'x' from foo where fooPK = 'valuePK') if number of rows inserted = 0, then the row already exists so do an update update foo set foo2 = 'value2' where fooPK = 'valuePK' Since I don't know what client interface you are using (java, perl, C), I can't give you exact code for this, but the above should be easily implemented in any language. thanks, --Barry Haller Christoph wrote: > Hi all, > Sorry for bothering you with my stuff for the second time > but I haven't got any answer within two days and the problem > appears fundamental, at least to me. > I have a C application running to deal with meteorological data > like temperature, precipitation, wind speed, wind direction, ... > And I mean loads of data like several thousand sets within every > ten minutes. >>From time to time it happens the transmitters have delivered wrong data, > so they send the sets again to be taken as correction. > The idea is to create a unique index on the timestamp, the location id > and the measurement id, then when receiving a duplicate key error > move on to an update command on that specific row. > But, within PostgreSQL this strategy does not work any longer within > a chained transaction, because the duplicate key error leads to > 'abort the whole transaction'. > What I can do is change from chained transaction to unchained transaction, > but what I have read in the mailing list so far, the commit operation > requires loads of cpu time, and I do not have time for this when > processing thousands of sets. > I am wondering now whether there is a fundamental design error in > my strategy. > Any ideas, suggestions highly appreciated and thanks for reading so far. > Regards, Christoph > > My first message: > In a C application I want to run several > insert commands within a chained transaction > (for faster execution). >>From time to time there will be an insert command > causing an > ERROR: Cannot insert a duplicate key into a unique index > > As a result, the whole transaction is aborted and all > the previous inserts are lost. > Is there any way to preserve the data > except working with "autocommit" ? > What I have in mind particularly is something like > "Do not abort on duplicate key error". > > ---------------------------(end of broadcast)--------------------------- > TIP 5: Have you checked our extensive FAQ? > > http://www.postgresql.org/users-lounge/docs/faq.html > >