Thread: pg_get_tabledef
Hi, <br /><br /> i was following a thread some time ago where adding a function <b>pg_get_tabledef</b> was one of the TODOsfor 8.2, but it somehow didn't make it to the release perhaps because the functionality was not clearly defined? notsure.<br /><br /> Anyway i happen to come up with a function for pg_get_tabledef which works something like following<br/><br /><i>postgres=# select pg_get_tabledef(16388) ;<br /> pg_get_tabledef <br /> --------------------------------<br/> CREATE TABLE public.dept<br /> (<br /> deptno numeric(2,0) NOT NULL,<br /> dname character varying(14),<br /> loc character varying(13)<br /> )<br /> WITHOUT OIDS;<br /></i>(1 row)<br /><br/><br /><br /> i wanted to submit a patch for this, IFF the community wants this function. The rationale is obviouslyto help Application developers writing applications like pgAdmin. Currently this part of SQL needs to be constructedmanually for postgres by the tools.<br /><br /> it is arguable that a table defintion will have constraints ,triggers etc as well, and they can be added without much problem, but i think if a tool needs to construct an SQL for alltable related objects then functions are already available for them like pg_get_constraintdef, pg_get_ruledef, pg_get_indexdef,pg_get_triggerdef etc<br /><br /> i understand that you guys don't like someone to develop a patch in isolationand just come up with it one day, but it really came out as a by-product of some other work , and i thought youguys might be interested in it.<br /><br /> if it is desired, i will submit a patch for it, within a day or so.<br /><br/> Regards,<br /> Usama Munir<br /> EnterpriseDB (<a class="moz-txt-link-abbreviated" href="http://www.enterprisedb.com">www.enterprisedb.com</a>)<br/><br /><br /><br />
Just a question, is there any advantage to having this then building a function in applications that wrap and use pg_dump with a few options? Surely that's a more appropriate way to achieve this functionality? - Naz. Usama Munir wrote: > Hi, > > i was following a thread some time ago where adding a function > *pg_get_tabledef* was one of the TODOs for 8.2, but it somehow didn't > make it to the release perhaps because the functionality was not > clearly defined? not sure. > > Anyway i happen to come up with a function for pg_get_tabledef which > works something like following > > /postgres=# select pg_get_tabledef(16388) ; > pg_get_tabledef > -------------------------------- > CREATE TABLE public.dept > ( > deptno numeric(2,0) NOT NULL, > dname character varying(14), > loc character varying(13) > ) > WITHOUT OIDS; > /(1 row) > > > > i wanted to submit a patch for this, IFF the community wants this > function. The rationale is obviously to help Application developers > writing applications like pgAdmin. Currently this part of SQL needs to > be constructed manually for postgres by the tools. > > it is arguable that a table defintion will have constraints , triggers > etc as well, and they can be added without much problem, but i think > if a tool needs to construct an SQL for all table related objects then > functions are already available for them like pg_get_constraintdef, > pg_get_ruledef, pg_get_indexdef, pg_get_triggerdef etc > > i understand that you guys don't like someone to develop a patch in > isolation and just come up with it one day, but it really came out as > a by-product of some other work , and i thought you guys might be > interested in it. > > if it is desired, i will submit a patch for it, within a day or so. > > Regards, > Usama Munir > EnterpriseDB (www.enterprisedb.com) > > >
Naz Gassiep <naz@mira.net> writes:
> Just a question, is there any advantage to having this then building a
> function in applications that wrap and use pg_dump with a few options?
> Surely that's a more appropriate way to achieve this functionality?
Refactoring pg_dump into some sort of library would clearly be a better
solution. Unfortunately it's also a huge amount of work :-(
There are several reasons why trying to push pg_dump's functionality
into the backend is largely doomed to failure:
* pg_dump needs to be able to dump from older server versions, and
having two completely different code paths for servers before and after
version X would be a mess.
* pg_dump can't consider a table as a monolithic object anyway; problems
like breaking circular dependencies involving DEFAULT expressions
require getting down-and-dirty with the constituent elements. If there
were a monolithic pg_get_table_def function, pg_dump couldn't use it.
* pg_dump ought to be dumping a snapshot of the DB as of its transaction
start time. Most of the backend's catalog access works on SnapshotNow
and hence fails this test. (I fear that we already have some issues
from the get_xxx_def functions that pg_dump uses now.)
regards, tom lane
I think using pg_dump in some cases is a good option , but not all the time, having a function makes it much cleaner touse<br /><br /> Consider pgAdmin lets say (and there are many such applications out there) , you need to show object DDLon the RHP and its nicely formatted and you can copy paste it and then perhaps export it in an SQL file.<br /><br /> Nowimagine you need to spawn a new process from inside the app for pg_dump, and then make it write to a file and then readthe file to display the object DDL, which is possible but very messy looking code. Then there are issues with launchingexternal processes on certain platforms (for example in Java if you start a new process from the runtime(), youneed to make sure you properly flush out its stdout and stderr streams otherwise it can go in a deadlock etc), i woulduse a function, if available anyday <br /><br /> Additionally there are such functions for other objects, but for tablesyou needed to construct it manually, so i also thought this would just complete the set and make it easier to writean SQL / DDL exporting app.<br /><br /><br /><br /> Naz Gassiep wrote: <blockquote cite="mid4651B51F.3000908@mira.net"type="cite"><pre wrap="">Just a question, is there any advantage to having this then buildinga function in applications that wrap and use pg_dump with a few options? Surely that's a more appropriate way to achieve this functionality? - Naz. Usama Munir wrote: </pre><blockquote type="cite"><pre wrap="">Hi, i was following a thread some time ago where adding a function *pg_get_tabledef* was one of the TODOs for 8.2, but it somehow didn't make it to the release perhaps because the functionality was not clearly defined? not sure. Anyway i happen to come up with a function for pg_get_tabledef which works something like following /postgres=# select pg_get_tabledef(16388) ; pg_get_tabledef --------------------------------CREATE TABLE public.dept( deptno numeric(2,0) NOT NULL, dname character varying(14), loc character varying(13))WITHOUT OIDS; /(1 row) i wanted to submit a patch for this, IFF the community wants this function. The rationale is obviously to help Application developers writing applications like pgAdmin. Currently this part of SQL needs to be constructed manually for postgres by the tools. it is arguable that a table defintion will have constraints , triggers etc as well, and they can be added without much problem, but i think if a tool needs to construct an SQL for all table related objects then functions are already available for them like pg_get_constraintdef, pg_get_ruledef, pg_get_indexdef, pg_get_triggerdef etc i understand that you guys don't like someone to develop a patch in isolation and just come up with it one day, but it really came out as a by-product of some other work , and i thought you guys might be interested in it. if it is desired, i will submit a patch for it, within a day or so. Regards, Usama Munir EnterpriseDB (<a class="moz-txt-link-abbreviated" href="http://www.enterprisedb.com">www.enterprisedb.com</a>) </pre></blockquote><pre wrap=""> ---------------------------(end of broadcast)--------------------------- TIP 5: don't forget to increase your free space map settings </pre></blockquote>
Usama Munir wrote: > I think using pg_dump in some cases is a good option , but not all the > time, having a function makes it much cleaner to use That's why having a shared pgdump library as has been previously mentioned is by far the best solution. We have discussed this before, and factoring out this functionality into a shared lib is what needs to be done. I'm not convinced it is as much work as Tom suggests, but it is certainly a non-trivial task. cheers andrew
When you say pgdump library, do you mean taking all catalog querying functionality into a contrib like module , exposed as functions and then have a simple pgdump executable which calls those functions to dump to a file, because you would still need a pgdump executable i suppose for people to be able to backup their stuff. Is my understanding somewhere near actual idea or i am way off here? Are there any discussions on this topic which could give me a little more idea? because i would definitely like to take a shot at this. Regards, Usama Munir EnterpriseDB (www.enterprisedb.com) Andrew Dunstan wrote: > > > Usama Munir wrote: >> I think using pg_dump in some cases is a good option , but not all >> the time, having a function makes it much cleaner to use > > That's why having a shared pgdump library as has been previously > mentioned is by far the best solution. > > We have discussed this before, and factoring out this functionality > into a shared lib is what needs to be done. I'm not convinced it is as > much work as Tom suggests, but it is certainly a non-trivial task. > > cheers > > andrew
I mean as a shared library - a .so for Unix (or whatever the flavor of unix uses instead) or a DLL on WIndows. And no, it would not be in contrib - as I mentioned in another thread yesterday I want to propose that contrib disappear. Certainly pg_dump would use the library, and retain all the file handling processing it does now. But we could also link it into psql, for example, and expose the results via \ commands. If you want to have a go at that you'll probably make lots of people very happy. cheers andrew Usama Munir wrote: > When you say pgdump library, do you mean taking all catalog querying > functionality into a contrib like module , exposed as functions and > then have a simple pgdump executable which calls those functions to > dump to a file, because you would still need a pgdump executable i > suppose for people to be able to backup their stuff. Is my > understanding somewhere near actual idea or i am way off here? > > > Are there any discussions on this topic which could give me a little > more idea? because i would definitely like to take a shot at this. > > Regards, > Usama Munir > EnterpriseDB (www.enterprisedb.com) > > > Andrew Dunstan wrote: >> >> >> Usama Munir wrote: >>> I think using pg_dump in some cases is a good option , but not all >>> the time, having a function makes it much cleaner to use >> >> That's why having a shared pgdump library as has been previously >> mentioned is by far the best solution. >> >> We have discussed this before, and factoring out this functionality >> into a shared lib is what needs to be done. I'm not convinced it is >> as much work as Tom suggests, but it is certainly a non-trivial task. >> >> cheers >> >> andrew >
Got it. Thanks for the clarification , i suppose the way you described it , it needs to go over libpq for the database interface, not the HeapTuple / Form_pg_* , way. I guess the way forward for me would be to crawl back in my corner, write up a mini - spec of how i intend to implement it and get back to you guys. Thanks for your feedback. Regards, Usama Munir. Andrew Dunstan wrote: > > I mean as a shared library - a .so for Unix (or whatever the flavor of > unix uses instead) or a DLL on WIndows. And no, it would not be in > contrib - as I mentioned in another thread yesterday I want to propose > that contrib disappear. > > Certainly pg_dump would use the library, and retain all the file > handling processing it does now. But we could also link it into psql, > for example, and expose the results via \ commands. > > If you want to have a go at that you'll probably make lots of people > very happy. > > cheers > > andrew > > > Usama Munir wrote: >> When you say pgdump library, do you mean taking all catalog querying >> functionality into a contrib like module , exposed as functions and >> then have a simple pgdump executable which calls those functions to >> dump to a file, because you would still need a pgdump executable i >> suppose for people to be able to backup their stuff. Is my >> understanding somewhere near actual idea or i am way off here? >> >> >> Are there any discussions on this topic which could give me a little >> more idea? because i would definitely like to take a shot at this. >> >> Regards, >> Usama Munir >> EnterpriseDB (www.enterprisedb.com) >> >> >> Andrew Dunstan wrote: >>> >>> >>> Usama Munir wrote: >>>> I think using pg_dump in some cases is a good option , but not all >>>> the time, having a function makes it much cleaner to use >>> >>> That's why having a shared pgdump library as has been previously >>> mentioned is by far the best solution. >>> >>> We have discussed this before, and factoring out this functionality >>> into a shared lib is what needs to be done. I'm not convinced it is >>> as much work as Tom suggests, but it is certainly a non-trivial task. >>> >>> cheers >>> >>> andrew >>
Usama Munir wrote: > Got it. Thanks for the clarification , i suppose the way you described > it , it needs to go over libpq for the database interface, not the > HeapTuple / Form_pg_* , way. > > Yes, for many reasons including those mentioned in Tom's email on this subject today. cheers andrew
"Usama Munir" <usama.munir@enterprisedb.com> writes:
> I guess the way forward for me would be to crawl back in my corner,
> write up a mini - spec of how i intend to implement it and get back to
> you guys.
Well, the *first* thing to do is read pg_dump for awhile. Until you've
grokked what it does to support multiple backend versions and how it
handles inter-object dependencies (dump ordering problems), you won't be
able to write a spec that has any credibility. In particular, the
business about breaking circular dependency loops is something I have
no idea how to handle in a simple "dump library" API.
regards, tom lane
Hi Usama, On May 21, 2007, at 9:20 AM, Usama Munir wrote: > i wanted to submit a patch for this, IFF the community wants this > function. The rationale is obviously to help Application developers > writing applications like pgAdmin. Currently this part of SQL needs > to be constructed manually for postgres by the tools. I would like to have this functionality (yesterday :) -- I'm currently working on this for pgEdit. Let me know if you need help with review or testing. John DeSoi, Ph.D. http://pgedit.com/ Power Tools for PostgreSQL