Re: Rename ShmemVariableCache and initialize it in more standard way

On 05/12/2023 05:40, Richard Guo wrote:
> On Tue, Dec 5, 2023 at 12:31 AM Tristan Partin <tristan@neon.tech> wrote:
>     On Mon Dec 4, 2023 at 6:49 AM CST, Heikki Linnakangas wrote:
>      > Here's a patch to allocate and initialize it with a pair of
>     ShmemSize
>      > and ShmemInit functions, like all other shared memory structs.
>      >
>      >  +        if (!IsUnderPostmaster)
>      >  +        {
>      >  +                Assert(!found);
>      >  +                memset(ShmemVariableCache, 0,
>     sizeof(VariableCacheData));
>      >  +        }
>      >  +        else
>      >  +                Assert(found);
> 
>> Should the else branch instead be a fatal log?
> 
> The Assert here seems OK to me.  We do the same when initializing
> commitTsShared/MultiXactState.  I think it would be preferable to adhere
> to this convention.

Right. I'm not 100% happy with that pattern either, but better be 
consistent.

There's a brief comment about this in CreateOrAttachShmemStructs():

>  * This is called by the postmaster or by a standalone backend.
>  * It is also called by a backend forked from the postmaster in the
>  * EXEC_BACKEND case.  In the latter case, the shared memory segment
>  * already exists and has been physically attached to, but we have to
>  * initialize pointers in local memory that reference the shared structures,
>  * because we didn't inherit the correct pointer values from the postmaster
>  * as we do in the fork() scenario.  The easiest way to do that is to run
>  * through the same code as before.  (Note that the called routines mostly
>  * check IsUnderPostmaster, rather than EXEC_BACKEND, to detect this case.
>  * This is a bit code-wasteful and could be cleaned up.)

The last sentence refers to this pattern.

>> Patches look good to me.
> 
> Also +1 to the patches.

Committed, thanks!

-- 
Heikki Linnakangas
Neon (https://neon.tech)