Thread: report expected contrecord size
A pretty minor issue: when reporting that WAL appears invalid because contrecord length doesn't match, we may as well print to the server log the value that we're expecting. Patch attached. -- Álvaro Herrera http://www.flickr.com/photos/alvherre/
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Alvaro Herrera <alvherre@2ndquadrant.com> writes:
> A pretty minor issue: when reporting that WAL appears invalid because
> contrecord length doesn't match, we may as well print to the server log
> the value that we're expecting. Patch attached.
ITYW
+ (long long) (total_len - gotlen),
just to be sure about what's getting casted to what. Otherwise +1.
regards, tom lane
On 2020-Sep-03, Tom Lane wrote: > Alvaro Herrera <alvherre@2ndquadrant.com> writes: > > A pretty minor issue: when reporting that WAL appears invalid because > > contrecord length doesn't match, we may as well print to the server log > > the value that we're expecting. Patch attached. > > ITYW > > + (long long) (total_len - gotlen), > > just to be sure about what's getting casted to what. Well, the intention there is to cast the first operand (which is uint32) so that it turns into signed 64-bits; the subtraction then occurs in 64 bit arithmetic normally. If I let the subtraction occur in 32-bit width unsigned, the result might overflow 32 bits. I'm thinking in 1 - UINT32_MAX or some such. Maybe to make that more explicit, it should be + ((long long) total_len) - gotlen, (If I understand the precedence correctly, it's the same thing I wrote). -- Álvaro Herrera https://www.2ndQuadrant.com/ PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services
Alvaro Herrera <alvherre@2ndquadrant.com> writes:
> Well, the intention there is to cast the first operand (which is uint32)
> so that it turns into signed 64-bits; the subtraction then occurs in 64
> bit arithmetic normally. If I let the subtraction occur in 32-bit width
> unsigned, the result might overflow 32 bits.
Uh ... is it really possible for gotlen to be more than total_len?
(I've not looked at the surrounding code here, but that seems weird.)
regards, tom lane
On 2020-Sep-03, Tom Lane wrote: > Alvaro Herrera <alvherre@2ndquadrant.com> writes: > > Well, the intention there is to cast the first operand (which is uint32) > > so that it turns into signed 64-bits; the subtraction then occurs in 64 > > bit arithmetic normally. If I let the subtraction occur in 32-bit width > > unsigned, the result might overflow 32 bits. > > Uh ... is it really possible for gotlen to be more than total_len? > (I've not looked at the surrounding code here, but that seems weird.) Well, as I understand, total_len comes from one page, and gotlen comes from the continuation record(s) in the next page(s) of WAL. So if things are messed up, it could happen. (This *is* the code that validates the record, so it can't make too many assumptions.) -- Álvaro Herrera https://www.2ndQuadrant.com/ PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services
Alvaro Herrera <alvherre@2ndquadrant.com> writes:
> On 2020-Sep-03, Tom Lane wrote:
>> Uh ... is it really possible for gotlen to be more than total_len?
>> (I've not looked at the surrounding code here, but that seems weird.)
> Well, as I understand, total_len comes from one page, and gotlen comes
> from the continuation record(s) in the next page(s) of WAL. So if
> things are messed up, it could happen. (This *is* the code that
> validates the record, so it can't make too many assumptions.)
Got it. No further objections.
regards, tom lane
On 2020-Sep-03, Tom Lane wrote: > Alvaro Herrera <alvherre@2ndquadrant.com> writes: > > On 2020-Sep-03, Tom Lane wrote: > >> Uh ... is it really possible for gotlen to be more than total_len? > >> (I've not looked at the surrounding code here, but that seems weird.) > > > Well, as I understand, total_len comes from one page, and gotlen comes > > from the continuation record(s) in the next page(s) of WAL. So if > > things are messed up, it could happen. (This *is* the code that > > validates the record, so it can't make too many assumptions.) > > Got it. No further objections. Many thanks for looking! Pushed now. -- Álvaro Herrera https://www.2ndQuadrant.com/ PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services