Re: [HACKERS] Regarding identifying a foreign scan
On Sun, Oct 7, 2012 at 10:29 AM, Tom Lane t...@sss.pgh.pa.us wrote: Atri Sharma atri.j...@gmail.com writes: Does that mean that using (some) global storage is the cause of the problem? If you're using global storage for state that needs to be replicated per-scan, yes, probably. But it's hard to be sure when you're being so vague about what you're doing. yeah -- the problem here is that Atri is not using ForeignScanState-fdw_state properly for storage (this in jdbc-fdw). I think he knows what to do -- he's going to fix it up. merlin -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
Re: [HACKERS] Regarding identifying a foreign scan
Atri Sharma atri.j...@gmail.com writes: Does that mean that using (some) global storage is the cause of the problem? If you're using global storage for state that needs to be replicated per-scan, yes, probably. But it's hard to be sure when you're being so vague about what you're doing. regards, tom lane -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
[HACKERS] Regarding identifying a foreign scan
Hi, I am trying to identify foreign scans uniquely.I am trying to do that by struct ForeignScanState,but I am confused as to how I can identify the scan. Is there a member of ForeignScanState that can be used for this purpose? Atri -- Regards, Atri l'apprenant -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
Re: [HACKERS] Regarding identifying a foreign scan
Atri Sharma atri.j...@gmail.com writes: I am trying to identify foreign scans uniquely. What do you mean by identify? What are you trying to accomplish, and in what context? regards, tom lane -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
Re: [HACKERS] Regarding identifying a foreign scan
On Sat, Oct 6, 2012 at 3:45 PM, Tom Lane t...@sss.pgh.pa.us wrote: Atri Sharma atri.j...@gmail.com writes: I am trying to identify foreign scans uniquely. What do you mean by identify? What are you trying to accomplish, and in what context? regards, tom lane Hi Tom, I am trying to identify the situation where a query has multiple foreign scans.In that case,I need to check whether the current scan is the same as a previous scan or not.If not,then I think it means that multiple scans are in progress on the same backend. Atri -- Regards, Atri l'apprenant -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
Re: [HACKERS] Regarding identifying a foreign scan
Atri Sharma atri.j...@gmail.com writes: On Sat, Oct 6, 2012 at 3:45 PM, Tom Lane t...@sss.pgh.pa.us wrote: Atri Sharma atri.j...@gmail.com writes: I am trying to identify foreign scans uniquely. What do you mean by identify? What are you trying to accomplish, and in what context? I am trying to identify the situation where a query has multiple foreign scans.In that case,I need to check whether the current scan is the same as a previous scan or not.If not,then I think it means that multiple scans are in progress on the same backend. Well, if you search the plan tree and find more than one ForeignScan node, it means there's more than one foreign scan. It doesn't seem to me to be very complicated. Now, if you're wondering whether they reference the same server or not, that's a bit harder. I guess you could look at the RTEs, fetch the foreign-table data for each FT relation OID, and see if the same server is referenced. regards, tom lane -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
Re: [HACKERS] Regarding identifying a foreign scan
On Sat, Oct 6, 2012 at 4:05 PM, Tom Lane t...@sss.pgh.pa.us wrote: Atri Sharma atri.j...@gmail.com writes: On Sat, Oct 6, 2012 at 3:45 PM, Tom Lane t...@sss.pgh.pa.us wrote: Atri Sharma atri.j...@gmail.com writes: I am trying to identify foreign scans uniquely. What do you mean by identify? What are you trying to accomplish, and in what context? I am trying to identify the situation where a query has multiple foreign scans.In that case,I need to check whether the current scan is the same as a previous scan or not.If not,then I think it means that multiple scans are in progress on the same backend. Well, if you search the plan tree and find more than one ForeignScan node, it means there's more than one foreign scan. It doesn't seem to me to be very complicated. Now, if you're wondering whether they reference the same server or not, that's a bit harder. I guess you could look at the RTEs, fetch the foreign-table data for each FT relation OID, and see if the same server is referenced. regards, tom lane Hi Tom, Thanks for the extensive reply. The issue I am trying to resolve is that if two scans are taking place on the same backend(due to the same query),then,the server is crashing. e.g. foreign_table is a foreign table SELECT * FROM foreign_table UNION SELECT * FROM foreign_table; results in a crash of the server. I think it is because I am not saving the state of the scan,so,if multiple scans a re running on the same backend,then,it is causing the crash. Any hints on how I can detect this condition please? Atri -- Regards, Atri l'apprenant -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
Re: [HACKERS] Regarding identifying a foreign scan
Atri Sharma atri.j...@gmail.com writes: The issue I am trying to resolve is that if two scans are taking place on the same backend(due to the same query),then,the server is crashing. That sounds like an FDW bug ... which FDW are we talking about? I think it is because I am not saving the state of the scan,so,if multiple scans a re running on the same backend,then,it is causing the crash. The FDW should certainly not assume that only one scan can happen at a time. I would not think this would be a problem as long as you're using reasonable coding techniques, like keeping scan-local state in scan-local storage and not globally. Any hints on how I can detect this condition please? If you are imagining that you'd do something differently depending on whether the current query contains multiple ForeignScan nodes for your FDW, that's still doomed to lose, because of nested queries. You really need to manage storage in a way that doesn't make assumptions of this sort. regards, tom lane -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
