Re: Conflict Detection and Resolution - Mailing list pgsql-hackers

On Fri, Sep 27, 2024 at 2:33 PM shveta malik <shveta.malik@gmail.com> wrote:
>
> On Fri, Sep 27, 2024 at 10:44 AM shveta malik <shveta.malik@gmail.com> wrote:
> >
> > > >
> > > > Thanks for the review.
> > > > Here is the v14 patch-set fixing review comments in [1] and [2].
> > > >
> > >
> > > Thanks for the patches. I am reviewing patch001, it is WIP, but please
> > > find initial set of comments:
> > >
> >

Please find next set of comments:

1)
parse_subscription_conflict_resolvers()

Shall we free 'SeenTypes' list at the end?

2)
General logic comment:
I think SetSubConflictResolver should also accept a list similar to
UpdateSubConflictResolvers() instead of array. Then we can even try
merging these 2 functions later (once we do this change, it will be
more clear). For SetSubConflictResolver to accept a list,
SetDefaultResolvers should give a list as output instead of an array
currently.

3)
Existing logic:
case ALTER_SUBSCRIPTION_RESET_ALL_CONFLICT_RESOLVERS:
{
ConflictTypeResolver conflictResolvers[CONFLICT_NUM_TYPES];

/* Remove the existing conflict resolvers. */
RemoveSubscriptionConflictResolvers(subid);

/*
* Create list of conflict resolvers and set them in the
* catalog.
*/
SetDefaultResolvers(conflictResolvers);
SetSubConflictResolver(subid, conflictResolvers, CONFLICT_NUM_TYPES);
}

Suggestion:
If we fix comment #2 and make SetSubConflictResolver and
SetDefaultResolvers to deal with list, then here we can get rid of
RemoveSubscriptionConflictResolvers(), we can simply make a default
list using SetDefaultResolvers and call UpdateSubConflictResolvers().
No need for 2 separate calls for delete and insert/set.

4)
Shall ResetConflictResolver() function also call
UpdateSubConflictResolvers internally? It will get rid of a lot code
duplication.

ResetConflictResolver()'s new approach could be:
a) validate conflict type and get enum value. To do this job, make a
sub-function validate_conflict_type() which will be called both from
here and from validate_conflict_type_and_resolver().
b) get default resolver for given conflict-type enum and then get
resolver string for that to help step c.
c) create a list of single element of ConflictTypeResolver and call
UpdateSubConflictResolvers.

5)
typedefs.list
ConflictResolver is missed?

6)
subscriptioncmds.c

/* Get the list of conflict types and resolvers and validate them. */
conflict_resolvers = GetAndValidateSubsConflictResolverList(stmt->resolvers);

No full stop needed in one line comment.  But since it is >80 chars,
it is good to split it to multiple lines and then full stop can be
retained.


7)
Shall we move the call to conf_detection_check_prerequisites() to
GetAndValidateSubsConflictResolverList() similar to how we do it for
parse_subscription_conflict_resolvers()? (I still prefer that
GetAndValidateSubsConflictResolverList and
parse_subscription_conflict_resolvers should be merged in the first
place. Array to list conversion as suggested in comment #2 will make
these two functions more similar, and then we can review to merge
them.)


8)
Shall parse_subscription_conflict_resolvers() be moved to conflict.c
as well? Or since it is subscription options' parsing, is it more
suited in the current file? Thoughts?

9)
Existing:
/*
 * Parsing function for conflict resolvers in CREATE SUBSCRIPTION command.
 * This function will report an error if mutually exclusive or duplicate
 * options are specified.
 */

Suggestion:
/*
 * Parsing function for conflict resolvers in CREATE SUBSCRIPTION command.
 *
 * In addition to parsing and validating the resolvers' configuration,
this function
 * also reports an error if mutually exclusive options are specified.
 */


10) Test comments (subscription.sql):

------
a)
-- fail - invalid conflict resolvers
CREATE SUBSCRIPTION regress_testsub CONNECTION
'dbname=regress_doesnotexist' PUBLICATION testpub CONFLICT RESOLVER
(insert_exists = foo) WITH (connect = false);

-- fail - invalid conflict types
CREATE SUBSCRIPTION regress_testsub CONNECTION
'dbname=regress_doesnotexist' PUBLICATION testpub CONFLICT RESOLVER
(foo = 'keep_local') WITH (connect = false);

We should swap the order of these 2 tests. Make it similar to ALTER tests.

b)
-- fail - invalid conflict resolvers
resolvers-->resolver

-- fail - invalid conflict types
types-->type

-- fail - duplicate conflict types
types->type

c)
-- creating subscription should create default conflict resolvers

Suggestion:
-- creating subscription with no explicit conflict resolvers should
configure default conflict resolvers

d)
-- ok - valid conflict type and resolvers
type-->types

e)
-- fail - altering with duplicate conflict types
types --> type
------


thanks
Shveta