[HACKERS] Phantom command ids again
Hi, I was about to resubmit the phantom command ids patch for review, as I noticed a little problem. In fmgr.c in record_C_func, we cache the xmin and cmin, and later in lookup_C_func we check that they match to determine if the cached information is still valid. With phantom command ids, the cmin is not valid outside the inserting transaction, which makes it unusable for that purpose. Similar caching code is used for other PL languages as well. The best solution I've come up with this far is to use the stored commandid, even if it's a phantom one, and a flag indicating if it's phantom or not. Any suggestions? -- Heikki Linnakangas EnterpriseDB http://www.enterprisedb.com ---(end of broadcast)--- TIP 1: if posting/reading through Usenet, please send an appropriate subscribe-nomail command to [EMAIL PROTECTED] so that your message can get through to the mailing list cleanly
Re: [HACKERS] Phantom command ids again
Heikki Linnakangas [EMAIL PROTECTED] writes: I was about to resubmit the phantom command ids patch for review, as I noticed a little problem. In fmgr.c in record_C_func, we cache the xmin and cmin, and later in lookup_C_func we check that they match to determine if the cached information is still valid. With phantom command ids, the cmin is not valid outside the inserting transaction, which makes it unusable for that purpose. I think that actually that's just belt-and-suspenders programming; it should be sufficient to compare tuple TID and xmin. AFAICS a single transaction cannot fill the same TID twice, since VACUUM would never dare remove a tuple entered by a still-in-progress transaction. So the cmin check doesn't seem necessary. regards, tom lane ---(end of broadcast)--- TIP 4: Have you searched our list archives? http://archives.postgresql.org
Re: [HACKERS] Phantom command ids again
Tom Lane wrote: Heikki Linnakangas [EMAIL PROTECTED] writes: I was about to resubmit the phantom command ids patch for review, as I noticed a little problem. In fmgr.c in record_C_func, we cache the xmin and cmin, and later in lookup_C_func we check that they match to determine if the cached information is still valid. With phantom command ids, the cmin is not valid outside the inserting transaction, which makes it unusable for that purpose. I think that actually that's just belt-and-suspenders programming; it should be sufficient to compare tuple TID and xmin. AFAICS a single transaction cannot fill the same TID twice, since VACUUM would never dare remove a tuple entered by a still-in-progress transaction. So the cmin check doesn't seem necessary. We don't currently use tid in the up-to-dateness check. Just Oid, xmin and cmin. Good point, tid would work. I'll change it do that in the patch. -- Heikki Linnakangas EnterpriseDB http://www.enterprisedb.com ---(end of broadcast)--- TIP 9: In versions below 8.0, the planner will ignore your desire to choose an index scan if your joining column's datatypes do not match
