Re: [Haskell-cafe] MySQL and HDBC?
Chris Waterson wrote: You probably already know this, but... you can mix tables from different storage engines in a single *statement*. Oh, no, I thought it was per database. Horrors! ...when a ROLLBACK has been issued against a non-transactional table... I could raise an error... perhaps this is preferable? John Goerzen wrote: ...what happens in the ODBC case depends on what the user puts in odbc.ini... either the full-on error treatment, or the ignoring the problem It does make sense for this to be configurable. In addition, you might want even more than the current full-on error mode: As Chris pointed out, throwing an exception at commit or rollback is a bit late - your data may already be destroyed by then. There should be a safe mode that raises an exception any time you try make a change to a non-transactional table, even before commit or rollback. That way, you would be able to write code like this: Start doing A in a new transaction. If any operation tries to make a change in a non-transactional table, roll back A and do B instead. Transactional safe mode could still allow reads of non-transactional tables. Is this possible for MySQL and/or ODBC? If you feel that the HDBC API needs to become more rich, I'm quite happy to entertain suggestions there Well, this makes a major difference in the meaning of a program. So it does seem that it should be possible at least to detect what is happening, or even control it programatically. In the case of a connection with less than guaranteed full support for transactions, you would want to be able to choose between the two behaviors available in the ODBC driver, or safe mode. Right now, the meaning of the dbTransactionSupport flag is ambiguous. Does True mean that full support for transactions is guaranteed? Or only that it might be supported for some tables? If not supported for some table, will the driver revert to irrevocable immediate changes, or raise an exception? Will silently ignore commit and rollback requests, or raise an exception? Even before the API becomes richer in this respect, the documentation should more clearly indicate the meaning of this flag (and drivers should then comply). Thanks, Yitz ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] MySQL and HDBC?
Yitzchak Gale wrote: Right now, the meaning of the dbTransactionSupport flag is ambiguous. Does True mean that full support for transactions is guaranteed? Or only that it might be supported for some tables? If not supported for some table, will the driver revert to irrevocable immediate changes, or raise an exception? Will silently ignore commit and rollback requests, or raise an exception? That is quite true. I had not realized that it was possible for this to vary within a MySQL database at the time I put that flag in. I believe MySQL is the only database people are likely to use with HDBC (even Sqlite has universal transaction support) that has this issue, so I would really encourage the community of MySQL users to come up with the API that would be most helpful in this situation, and as I said, I'm happy to add it to HDBC. -- John ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] MySQL and HDBC?
Duncan Coutts wrote: This was uploaded to hackage yesterday: http://hackage.haskell.org/cgi-bin/hackage-scripts/package/HDBC-mysql-0.1 This is wonderful news! Whatever we might say about MySQL, it is so ubiquitous that this driver is really important for Haskell. Chris, please keep us up-to-date with your progress. Chris Waterson wrote: I would very much appreciate feedback. I'm still working with John Goerzen (who has been extremely helpful) to iron our some details, see [1] for a list of issues that you should be aware of before you start doing anything too serious... Well whatever John says will obviously take priority. But the following two points that you list are covered in the API docs on the main Haddock page for HDBC: http://software.complete.org/static/hdbc/doc/Database-HDBC.html o Transactions - if a connection does not support transactions, dbTransactionSupport should return False, and commit and rollback should raise errors. (SqlError I suppose?) Not warnings. o Threading - see the section at the bottom of the Haddock page for a nice specification of what the driver needs and does not need to support. Also - o Non-ASCIIText - OK for now, but MySQL has significant support for Unicode and encodings, so that should be on the to-do list. All of the rest of your to-do items sound great. Thanks, Yitz ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] MySQL and HDBC?
On Jan 25, 2009, at 4:25 AM, Yitzchak Gale wrote: o Transactions - if a connection does not support transactions, dbTransactionSupport should return False, and commit and rollback should raise errors. (SqlError I suppose?) Not warnings. You probably already know this, but...the problem is that the connection doesn't really have anything to do with supporting transactions in MySQL; the storage engine that backs a particular table does. A single connection can interact with tables that are backed by a variety of different storage engines. In fact, you can mix tables from different storage engines in a single *statement*. To strictly implement HDBC's semantics, I could report that a MySQL connection doesn't support transactions, ever. Internally, I'd turn on auto-commit to force each statement to run in its own transaction, always. This is certainly correct, however, it severely limits the utility of the driver IMO. For now, I've opted to do (essentially) what the ODBC driver does with MySQL connections. Namely, I trust the programmer to use the driver correctly, and fail silently if he misuses this privilege. I don't love this, but it seems to be the way MySQL is generally dealt with in other languages. It is possible for me to detect when a ROLLBACK has been issued against a non-transactional table. In this case, I could raise an error; however, doing this would be different behavior than the ODBC driver. (Besides being too late for the programmer to do anything about it!) But perhaps this is preferable? o Threading - see the section at the bottom of the Haddock page for a nice specification of what the driver needs and does not need to support. Gah. I don't know how I missed this. Thanks for pointing it out. Also - o Non-ASCIIText - OK for now, but MySQL has significant support for Unicode and encodings, so that should be on the to-do list. Agreed. thanks! chris ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] MySQL and HDBC?
Chris Waterson wrote: You probably already know this, but...the problem is that the connection doesn't really have anything to do with supporting transactions in MySQL; the storage engine that backs a particular table does. A single connection can interact with tables that are backed by a variety of different storage engines. In fact, you can mix tables from different storage engines in a single *statement*. ... for which you have my complete sympathies ;-) It is possible for me to detect when a ROLLBACK has been issued against a non-transactional table. In this case, I could raise an error; however, doing this would be different behavior than the ODBC driver. (Besides being too late for the programmer to do anything about it!) But perhaps this is preferable? To be sure, what happens in the ODBC case depends on what the user puts in odbc.ini. The user can indicate for either the full-on error treatment, or the ignoring the problem for non-transactional tables. In any case, you and the MySQL user community are probably in a better position to determine what is the most sensible course of action here too. If you feel that the HDBC API needs to become more rich, I'm quite happy to entertain suggestions there too. o Non-ASCIIText - OK for now, but MySQL has significant support for Unicode and encodings, so that should be on the to-do list. There has been recent work in the PostgreSQL backend that could perhaps be a constructive example. -- John ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] MySQL and HDBC?
2009/1/23 Galchin, Vasili vigalc...@gmail.com Hello, Real World Haskell seems to say that the abstraction layer HDBC doesn't support MySQL. If so, in what sense doesn't HDBC support MySQL?? It doesn't have a MySQL backend. However, it does have an ODBC backend which should work fine with MySQL. -- Sebastian Sylvan +44(0)7857-300802 UIN: 44640862 ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] MySQL and HDBC?
On Fri, 2009-01-23 at 08:06 +, Sebastian Sylvan wrote: 2009/1/23 Galchin, Vasili vigalc...@gmail.com Hello, Real World Haskell seems to say that the abstraction layer HDBC doesn't support MySQL. If so, in what sense doesn't HDBC support MySQL?? It doesn't have a MySQL backend. However, it does have an ODBC backend which should work fine with MySQL. This was uploaded to hackage yesterday: http://hackage.haskell.org/cgi-bin/hackage-scripts/package/HDBC-mysql-0.1 You might like to test it and give feedback to the author. Duncan ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] MySQL and HDBC?
ok .. thank you. Vasili On Fri, Jan 23, 2009 at 3:23 AM, Duncan Coutts duncan.cou...@worc.ox.ac.ukwrote: On Fri, 2009-01-23 at 08:06 +, Sebastian Sylvan wrote: 2009/1/23 Galchin, Vasili vigalc...@gmail.com Hello, Real World Haskell seems to say that the abstraction layer HDBC doesn't support MySQL. If so, in what sense doesn't HDBC support MySQL?? It doesn't have a MySQL backend. However, it does have an ODBC backend which should work fine with MySQL. This was uploaded to hackage yesterday: http://hackage.haskell.org/cgi-bin/hackage-scripts/package/HDBC-mysql-0.1 You might like to test it and give feedback to the author. Duncan ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] MySQL and HDBC?
On Jan 23, 2009, at 1:23 AM, Duncan Coutts wrote: On Fri, 2009-01-23 at 08:06 +, Sebastian Sylvan wrote: 2009/1/23 Galchin, Vasili vigalc...@gmail.com Hello, Real World Haskell seems to say that the abstraction layer HDBC doesn't support MySQL. If so, in what sense doesn't HDBC support MySQL?? It doesn't have a MySQL backend. However, it does have an ODBC backend which should work fine with MySQL. This was uploaded to hackage yesterday: http://hackage.haskell.org/cgi-bin/hackage-scripts/package/HDBC-mysql-0.1 You might like to test it and give feedback to the author. I would very much appreciate feedback. I'm still working with John Goerzen (who has been extremely helpful) to iron our some details, see [1] for a list of issues that you should be aware of before you start doing anything too serious. thanks! chris [1] http://www.maubi.net/~waterson/hacks/hdbc-mysql.html ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] MySQL and HDBC?
On Fri, 2009-01-23 at 03:54 -0600, Galchin, Vasili wrote: On Fri, Jan 23, 2009 at 3:23 AM, Duncan Coutts duncan.cou...@worc.ox.ac.uk wrote: This was uploaded to hackage yesterday: http://hackage.haskell.org/cgi-bin/hackage-scripts/package/HDBC-mysql-0.1 You might like to test it and give feedback to the author. ooops ... cabal install HDBC-mysql doesn't work ?? Vasili Vasili, it's really no good telling me this, especially since you did not cc the author or haskell-cafe. I am not the author of the package. And even if I were you have provided no details on what goes wrong. I'm sure it was not your intention, but to some people your response would sound demanding and unhelpful, possibly even rude. Make sure that when you do contact the author that you send them something that they will find helpful. So when you email the author make sure you provide full details about what you did and about the environment you are using, eg platform, ghc version, where your mysql libraries are installed, what version they are etc. I would guess that the most likely problem is that you do not have the mysql development package installed. It should provide the mysql_config program. If that is not the problem then contact the package author with the full details. Duncan ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] MySQL and HDBC?
On Fri, 2009-01-23 at 03:54 -0600, Galchin, Vasili wrote: ooops ... cabal install HDBC-mysql doesn't work ?? for what it's worth, calbal install hdbc-mysql worked on my office's pc. ( kubuntu 8.10 ) ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] MySQL and HDBC?
Hello, Real World Haskell seems to say that the abstraction layer HDBC doesn't support MySQL. If so, in what sense doesn't HDBC support MySQL?? Thanks, Vasili ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
