Thread: Re: printTable API (was: Show INHERIT in \du)
On Sun, Mar 30, 2008 at 9:39 AM, Brendan Jurd <direvus@gmail.com> wrote:
> On 25/03/2008, Tom Lane <tgl@sss.pgh.pa.us> wrote:
> > "Brendan Jurd" <direvus@gmail.com> writes:
> > > This makes me wonder whether print.c could offer something a bit more
> > > helpful to callers wishing to DIY a table; we could have a
> > > table-building struct with methods like addHeader and addCell.
> >
> > Once you have two occurrences of a pattern, it's reasonable to assume
> > there will be more later. +1 for building a little bit of infrastructure.
> >
>
> Per the above discussion, I'm looking at creating a nice API in
> print.c for callers wishing to build their own psql output table.
>
> Currently, if you want to build your own table you need to implement
> your own local version of the logic in printQuery.
> describeOneTableDetails is the only place this happens right now, but
> due to some localisation issues it looks like my \du patch will have
> to build its table manually as well.
>
I'd like to submit my first version of this patch for review. I have
introduced a new struct in print.h called printTableContent, which is
used to compose the contents of a psql table. The methods exposed for
this struct are as follows:
void printTableInit(printTableContent *const content, const char *title,
const int ncolumns, const int nrows);
void printTableAddHeader(printTableContent *const content, const char *header,
const int encoding, const bool translate, const char align);
void printTableAddCell(printTableContent *const content, const char *cell,
const int encoding, const bool translate);
void printTableAddFooter(printTableContent *const content, const char *footer);
void printTableSetFooter(printTableContent *const content, const char *footer);
void printTableCleanUp(printTableContent *const content);
-= Notes
The column headers and cells are implemented as simple arrays of
pointers to existing strings. It's necessary for the calling site to
ensure that these strings survive at least until the table has been
printed. That's usually not a problem since the headers and cells
tend to be inside a PGresult.
Footers are a bit different. I've implemented them as a very
primitive singly-linked list which copies its contents with strdup. A
lot of the complexity in the pre-patch describeOneTableDetails comes
from the fact that it needs to know the number of footers in advance.
The singly-linked list allows callers to incrementally add an
arbitrary number of footers, and doesn't require them to preserve the
strings, which is nice when you're working with a temporary
PQExpBuffer to produce a footer.
-= QA
Not having written much C, I'm concerned about memory management
errors. But I've run my own tests with describeOneTableDetails on
tables with every kind of footer there is, and put the patch through
valgrind, and I haven't encountered any segfaults or memory leaks.
Both the serial and parallel regression tests passed perfectly.
-= Documentation
None required as far as I can tell, aside from code comments.
-= Patch tracking
I'll add this to the May CommitFest wiki page myself -- Bruce, you
don't need to do anything at all! =)
Looking forward to your comments.
Cheers,
BJ
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Brendan Jurd escribió: > I'd like to submit my first version of this patch for review. I have > introduced a new struct in print.h called printTableContent, which is > used to compose the contents of a psql table. The methods exposed for > this struct are as follows: Looks cool -- on a first read, I think you should add some more code comments at the top of each function specifying whether the texts need to be translated by the caller or done by the function itself. Also it would be good if it is consistent, too :-) -- Alvaro Herrera http://www.CommandPrompt.com/ PostgreSQL Replication, Consulting, Custom Development, 24x7 support
-----BEGIN PGP SIGNED MESSAGE----- Hash: SHA1 On Mon, Apr 14, 2008 at 6:03 AM, Alvaro Herrera wrote: > Looks cool -- on a first read, I think you should add some more code > comments at the top of each function specifying whether the texts need > to be translated by the caller or done by the function itself. Also it > would be good if it is consistent, too :-) > Thanks for your feedback Alvaro. Taking a look at this with fresh eyes, I realised it was daft to pass the encoding to each AddHeader and AddCell call, since the encoding isn't going to change between cells. Instead I put a pointer to a printTableOpt inside the printTableContent. The Opt struct contains the encoding and the Add functions refer to the encoding internally when adding items. This also has the benefit that you don't need to pass a printTableOpt separately to the functions that actually do the printing. Per your suggestion, I fleshed out the comments on translation, in particular explaining why AddHeader and AddCell have an option for translation but AddFooter does not. The second version of the patch is attached. Now my question is, how do I indicate that a second version of the patch has been submitted on the wiki? Should I leave the primary link pointing at the original submission, or update it to point at this message? Cheers, BJ -----BEGIN PGP SIGNATURE----- Version: GnuPG v2.0.7 (GNU/Linux) Comment: http://getfiregpg.org iD8DBQFIBGMz5YBsbHkuyV0RArf1AJwOsz2Wq5g7vg6DvyOzD7Ixsgl8EgCg4HyZ sxtmc2A5FYiwYkkrhfpDsDM= =jvKI -----END PGP SIGNATURE-----
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On Tue, Apr 15, 2008 at 06:11:32PM +1000, Brendan Jurd wrote: > Now my question is, how do I indicate that a second version of the > patch has been submitted on the wiki? Should I leave the primary link > pointing at the original submission, or update it to point at this > message? I'd say add a row: New version submitted (link) (brief summary of changes) If there are many more versions you can consider cutting, but you're not there yet. Have a nice day, -- Martijn van Oosterhout <kleptog@svana.org> http://svana.org/kleptog/ > Please line up in a tree and maintain the heap invariant while > boarding. Thank you for flying nlogn airlines.
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Brendan Jurd escribió: > The second version of the patch is attached. Thanks. I looked the patch over and did some minor changes. Modified version attached. One thing I'm not entirely happy about is the fact that we need a pointer to the last footer/cell/header, so two pointers for each element kind. -- Alvaro Herrera http://www.CommandPrompt.com/ The PostgreSQL Company - Command Prompt, Inc.
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-----BEGIN PGP SIGNED MESSAGE----- Hash: SHA1 On Thu, Apr 17, 2008 at 7:27 AM, Alvaro Herrera wrote: > Brendan Jurd escribió: > > > The second version of the patch is attached. > > Thanks. I looked the patch over and did some minor changes. Modified > version attached. > Cool, I had a look through your changes and they all seemed fine to me. In particular, moving the header comments to the ... header ... file seemed like a smart move. =) > One thing I'm not entirely happy about is the fact that we need a > pointer to the last footer/cell/header, so two pointers for each element > kind. > Well, the alternative is iterating through the array each time you want to add something until you hit a NULL pointer, and adding the new item at that point. Considering we're only chewing up an extra 4 * sizeof(pointer) = 16 bytes in the struct, it seems like a reasonable price to pay for the convenience. What is it about the extra fields that makes you unhappy? Cheers, BJ -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.4.7 (GNU/Linux) Comment: http://getfiregpg.org iD8DBQFIBo2y5YBsbHkuyV0RAmLhAJ9CP/9L1Nv7WbCtrCYu6tyoGhQItQCeMRm0 HegSSBq8tXw43Kj2xeQ2RCs= =RvzP -----END PGP SIGNATURE-----
Brendan Jurd escribió: > On Thu, Apr 17, 2008 at 7:27 AM, Alvaro Herrera wrote: > > One thing I'm not entirely happy about is the fact that we need a > > pointer to the last footer/cell/header, so two pointers for each > > element kind. > > Well, the alternative is iterating through the array each time you > want to add something until you hit a NULL pointer, and adding the new > item at that point. Considering we're only chewing up an extra 4 * > sizeof(pointer) = 16 bytes in the struct, it seems like a reasonable > price to pay for the convenience. Well, consider that there are going to be 1 or 2 entries in the arrays in most cases anyway :-) Well, as far as footers go anyway ... I just realized that in all other cases it will certainly be the wrong thing to do :-) Still, perhaps a integer count is better? > What is it about the extra fields that makes you unhappy? I don't know if "unnecessarity" is a word, but I hope you get what I mean :-) -- Alvaro Herrera http://www.CommandPrompt.com/ PostgreSQL Replication, Consulting, Custom Development, 24x7 support
-----BEGIN PGP SIGNED MESSAGE----- Hash: SHA1 On Thu, Apr 17, 2008 at 9:53 AM, Alvaro Herrera wrote: > > Well, consider that there are going to be 1 or 2 entries in the arrays > in most cases anyway :-) Well, as far as footers go anyway ... I just > realized that in all other cases it will certainly be the wrong thing to > do :-) Still, perhaps a integer count is better? > I oscillated between using an integer and a pointer for ->header and - ->cell while I was writing the code. In the end I went with pointer simply because it makes the iterations nicer looking, and there's a symmetry in having the "first item" and "last item" pointers be the same type. If there's some technical reason that integers would be better, I'll all ears, but from an aesthetic/code readability perspective I like the pointer. > > Brendan Jurd escribió: > > What is it about the extra fields that makes you unhappy? > > I don't know if "unnecessarity" is a word, but I hope you get what I > mean :-) Since the footers list is usually pretty short, you could make an argument for dropping the "last footer" pointer and just iterating through the list to find the last element every time you want to do something with footers. And to do that, you'd have to declare a temporary pointer inside the AddFooter function anyway, so you're not getting rid of the pointer so much as making it slightly more transient. All that having been said, C isn't my native language. So if the pointer is indeed wasteful I'm happy to cede to the wisdom of more experienced C coders. Cheers, BJ -----BEGIN PGP SIGNATURE----- Version: GnuPG v2.0.7 (GNU/Linux) Comment: http://getfiregpg.org iD8DBQFIBw7m5YBsbHkuyV0RAv4IAJ0cKrziZpNWkVV7LxFhlV/V5L0pJACfUtZ+ cVbcjL1e89j21JDZJBVdBqw= =Nzr+ -----END PGP SIGNATURE-----
Brendan Jurd escribió: > On Thu, Apr 17, 2008 at 7:27 AM, Alvaro Herrera wrote: > > Thanks. I looked the patch over and did some minor changes. Modified > > version attached. > > Cool, I had a look through your changes and they all seemed fine to > me. In particular, moving the header comments to the ... header ... > file seemed like a smart move. =) FWIW I just noticed something else. With this patch we add pg_strdup calls into print.c. pg_strdup lives in common.c. This is fine as psql is concerned, but we have another problem which is that in bin/scripts there are two programs that want to use printQuery(). The problem is that there's no pg_strdup there :-( The easy solution is to add pg_strdup to bin/scripts/common.c, but there we don't have a global progname, so the error report in the out of memory case cannot carry the name of the program crashing. I don't like that, but I don't see any other solution. Ideas welcome. -- Alvaro Herrera http://www.CommandPrompt.com/ PostgreSQL Replication, Consulting, Custom Development, 24x7 support
Hi guys, Here's the latest version of the printTable API. This version is against the current HEAD and merges in the changes made by the recently committed psql wrap patch. This version also includes Alvaro's fix for the issue of pg_strdup not being available to programs in scripts/ (as quoted below). Clean compile and all regression tests passed on amd64 gentoo. Cheers, BJ On Thu, May 8, 2008 at 7:55 AM, Alvaro Herrera <alvherre@commandprompt.com> wrote: > FWIW I just noticed something else. With this patch we add pg_strdup > calls into print.c. pg_strdup lives in common.c. > > This is fine as psql is concerned, but we have another problem which is > that in bin/scripts there are two programs that want to use > printQuery(). The problem is that there's no pg_strdup there :-( > > The easy solution is to add pg_strdup to bin/scripts/common.c, but there > we don't have a global progname, so the error report in the out of > memory case cannot carry the name of the program crashing. > > I don't like that, but I don't see any other solution. Ideas welcome. > > -- > Alvaro Herrera http://www.CommandPrompt.com/ > PostgreSQL Replication, Consulting, Custom Development, 24x7 support >
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Brendan Jurd escribió: > Here's the latest version of the printTable API. This version is > against the current HEAD and merges in the changes made by the > recently committed psql wrap patch. > > This version also includes Alvaro's fix for the issue of pg_strdup not > being available to programs in scripts/ (as quoted below). Thanks. I had to merge Tom's fixes to the wrap code too. Another thing that I changed is that now "not null" and "default %s" is translatable in a table description. Also, I removed the _() call around things like "?%c? \"%s.%s\"", which is what we use for tables of which we don't recognize the relkind. Thanks for the patch. -- Alvaro Herrera http://www.CommandPrompt.com/ The PostgreSQL Company - Command Prompt, Inc.