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

Thanks for this patch! I have implemented this pattern several times,
so this is really helpful.

I have a few early comments, but I plan on trying this out next.

1/
> > +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?

NamedLWLockTrancheRequest uses NAMEDATALEN = 64 bytes for the
tranche_name

typedef struct NamedLWLockTrancheRequest
{
char tranche_name[NAMEDATALEN];
int num_lwlocks;
} NamedLWLockTrancheRequest;

but in the case here, "_dsa" or "_dsh" will occupy another 4 bytes.
I think instead of hardcoding, we should #define a length,

i.e. #define NAMEDDSMTRANCHELEN (NAMEDATALEN + 4)

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);

3/ It will be good to "Assert(dsh)" before "return dsh;" for safety?

MemoryContextSwitchTo(oldcontext);
LWLockRelease(DSMRegistryLock);

return dsh;
}

--
Sami Imseih
Amazon Web Services (AWS)