Re: add function for creating/attaching hash table in DSM registry

On Thu, Jun 05, 2025 at 01:38:25PM -0500, Sami Imseih wrote:
> I have a few early comments, but I plan on trying this out next.

Thanks for reviewing.

>> > +typedef struct NamedDSMHashState
>> > +{
>> > +     dsa_handle      dsah;
>> > +     dshash_table_handle dshh;
>> > +     int                     dsa_tranche;
>> > +     char            dsa_tranche_name[68];   /* name + "_dsa" */
>> > +     int                     dsh_tranche;
>> > +     char            dsh_tranche_name[68];   /* name + "_dsh" */
>> > +} NamedDSMHashState;
>>
>> I don't have enough knowledge to review the rest of the patch, but
>> shouldn't this use NAMEDATALEN, rather than hard-coding the default
>> length?

I straightened this out in v2.  I've resisted using NAMEDATALEN because
this stuff is unrelated to the name type.  But I have moved all the lengths
and suffixes to macros.

> NamedLWLockTrancheRequest uses NAMEDATALEN = 64 bytes for the
> tranche_name
> 
> typedef struct NamedLWLockTrancheRequest
> {
> char tranche_name[NAMEDATALEN];
> int num_lwlocks;
> } NamedLWLockTrancheRequest;

I think the NAMEDATALEN limit only applies to tranches requested at startup
time.  LWLockRegisterTranche() just saves whatever pointer you give it, so
AFAICT there's no real limit there.

> 2/ Can you group the dsa and dsh separately. I felt this was a bit
> difficult to read?
> 
> +               /* Initialize LWLock tranches for the DSA and dshash table. */
> +               state->dsa_tranche = LWLockNewTrancheId();
> +               state->dsh_tranche = LWLockNewTrancheId();
> +               sprintf(state->dsa_tranche_name, "%s_dsa", name);
> +               sprintf(state->dsh_tranche_name, "%s_dsh", name);
> +               LWLockRegisterTranche(state->dsa_tranche,
> state->dsa_tranche_name);
> +               LWLockRegisterTranche(state->dsh_tranche,
> state->dsh_tranche_name);

Done.

> 3/ It will be good to "Assert(dsh)" before "return dsh;" for safety?
> 
>     MemoryContextSwitchTo(oldcontext);
>     LWLockRelease(DSMRegistryLock);
> 
>     return dsh;

Eh, I would expect the tests to start failing horribly if I managed to mess
that up.

-- 
nathan