On 16 August 2017 at 03:42, Tomas Vondra <tomas.von...@2ndquadrant.com> wrote:
> > > On 08/15/2017 07:54 PM, Robert Haas wrote: > >> On Tue, Aug 15, 2017 at 9:59 AM, Tomas Vondra >> <tomas.von...@2ndquadrant.com> wrote: >> >>> I don't think so -- the "committed" and "invalid" meanings are >>>> effectively canceled when the "frozen" mask is present. >>>> >>>> I mean, "committed" and "invalid" contradict each other... >>>> >>> >>> FWIW I agree with Craig - the functions should output the masks raw, >>> without >>> any filtering. The reason is that when you're investigating data >>> corruption >>> or unexpected behavior, all this is very useful when reasoning about what >>> might (not) have happened. >>> >>> Or at least make the filtering optional. >>> >> >> I don't think "filtering" is the right way to think about it. It's >> just labeling each combination of bits with the meaning appropriate to >> that combination of bits. >> >> I mean, if you were displaying the contents of a CLOG entry, would you >> want the value 3 to be displayed as COMMITTED ABORTED SUBCOMMITTED >> because TRANSACTION_STATUS_COMMITTED|TRANSACTION_STATUS_ABORTED == >> TRANSACTION_STATUS_SUB_COMMITTED? >> >> I realize that you may be used to thinking of the HEAP_XMIN_COMMITTED >> and HEAP_XMAX_COMMITTED bits as two separate bits, but that's not >> really true any more. They're a 2-bit field that can have one of four >> values: committed, aborted, frozen, or none of the above. >> >> > All I'm saying is that having the complete information (knowing which bits > are actually set in the bitmask) is valuable when reasoning about how you > might have gotten to the current state. Which I think is what Craig is > after. > > What I think we should not do is interpret the bitmasks (omitting some of > the information) assuming all the bits were set correctly. I agree, and the patch already does half of this: it can output just the raw bit flags, or it can interpret them to show HEAP_XMIN_FROZEN etc. So the required change, which seems to have broad agreement, is to have the "interpret the bits" mode show only HEAP_XMIN_FROZEN when it sees HEAP_XMIN_COMMITTED|HEAP_XMIN_INVALID, etc. We can retain raw-flags output as-is for when seriously bogus state is suspected. Any takers? -- Craig Ringer http://www.2ndQuadrant.com/ PostgreSQL Development, 24x7 Support, Training & Services
