Thread: Redundant strlen(query) in get_rel_infos
Hi. While reviewing another patch to the file info.c, I noticed there seem to be some unnecessary calls to strlen(query) in get_rel_infos() function. i.e. The query is explicitly initialized to an empty string immediately prior, so why the strlen? PSA patch for this. ------ Kind Regards, Peter Smith. Fujitsu Australia
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On Thu, May 11, 2023 at 01:06:42PM +1000, Peter Smith wrote: > While reviewing another patch to the file info.c, I noticed there seem > to be some unnecessary calls to strlen(query) in get_rel_infos() > function. > > i.e. The query is explicitly initialized to an empty string > immediately prior, so why the strlen? It just looks like this was copied from a surrounding area like get_db_infos(). Keeping the code as it is is no big deal, either, but yes we could just remove them and save the two calls. So ok by me. -- Michael
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> On 11 May 2023, at 06:24, Michael Paquier <michael@paquier.xyz> wrote: > > On Thu, May 11, 2023 at 01:06:42PM +1000, Peter Smith wrote: >> While reviewing another patch to the file info.c, I noticed there seem >> to be some unnecessary calls to strlen(query) in get_rel_infos() >> function. >> >> i.e. The query is explicitly initialized to an empty string >> immediately prior, so why the strlen? > > It just looks like this was copied from a surrounding area like > get_db_infos(). Keeping the code as it is is no big deal, either, but > yes we could just remove them and save the two calls. So ok by me. I think it's intentionally done in 73b9952e82 as defensive coding, and given that this is far from a hot codepath I think leaving them is better. Instead I think it would be more worthwhile to remove these snprintf() made queries and use PQExpbuffers. 29aeda6e4e6 introduced that in pg_upgrade and it is more in line with how we build queries in other tools. Looking at the snprintf sites made me remember a patchset I worked on last year (but I don't remember if I ended up submitting); there is no need to build one of the queries on the stack as it has no variables. The attached 0003 (which needs a reindent of the query text) comes from that patchset. I think we should do this regardless. -- Daniel Gustafsson
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On Thu, May 11, 2023 at 11:57:37AM +0200, Daniel Gustafsson wrote: > I think it's intentionally done in 73b9952e82 as defensive coding, and given > that this is far from a hot codepath I think leaving them is better. > > Instead I think it would be more worthwhile to remove these snprintf() made > queries and use PQExpbuffers. 29aeda6e4e6 introduced that in pg_upgrade and it > is more in line with how we build queries in other tools. Good idea to reduce the overall presence of QUERY_ALLOC in the surroundings. > Looking at the snprintf sites made me remember a patchset I worked on last year > (but I don't remember if I ended up submitting); there is no need to build one > of the queries on the stack as it has no variables. The attached 0003 (which > needs a reindent of the query text) comes from that patchset. I think we > should do this regardless. Not sure that this is an improvement in itself as get_tablespace_paths() includes QUERY_ALLOC because executeQueryOrDie() does so, so this could become a problem if someones decides to copy-paste this code with a query becomes longer than QUERY_ALLOC once built? Perhaps that's not worth worrying, but I like your suggestion of applying more PQExpbuffers, particularly if applied in a consistent way across the board. It could matter if the code of get_tablespace_paths() is changed to use a query with parameters. -- Michael
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> On 15 May 2023, at 09:45, Michael Paquier <michael@paquier.xyz> wrote: > On Thu, May 11, 2023 at 11:57:37AM +0200, Daniel Gustafsson wrote: >> Looking at the snprintf sites made me remember a patchset I worked on last year >> (but I don't remember if I ended up submitting); there is no need to build one >> of the queries on the stack as it has no variables. The attached 0003 (which >> needs a reindent of the query text) comes from that patchset. I think we >> should do this regardless. > > Not sure that this is an improvement in itself as > get_tablespace_paths() includes QUERY_ALLOC because > executeQueryOrDie() does so, so this could become a problem if > someones decides to copy-paste this code with a query becomes longer > than QUERY_ALLOC once built? Perhaps that's not worth worrying, We already have lots of invocations of executeQueryOrDie which doesn't pass via a QUERY_ALLOC buffer so I don't see any risk with adding one more. -- Daniel Gustafsson