Re: [HACKERS] [PATCH] Lockable views

On Thu, 29 Mar 2018 17:26:36 -0700
Andres Freund <andres@anarazel.de> wrote:

Thank you for your comments. I attach a patch to fix issues
you've pointed out.

> Hi,
> 
> On 2018-03-28 20:26:48 +0900, Yugo Nagata wrote:
> > diff --git a/doc/src/sgml/ref/lock.sgml b/doc/src/sgml/ref/lock.sgml
> > index b2c7203..96d477c 100644
> > --- a/doc/src/sgml/ref/lock.sgml
> > +++ b/doc/src/sgml/ref/lock.sgml
> > @@ -46,6 +46,11 @@ LOCK [ TABLE ] [ ONLY ] <replaceable class="parameter">name</replaceable> [ * ]
> >    </para>
> >  
> >    <para>
> > +   When a view is specified to be locked, all relations appearing in the view
> > +   definition query are also locked recursively with the same lock mode. 
> > +  </para>
> 
> Trailing space added. I'd remove "specified to be" from the sentence.

Fixed.

> 
> I think mentioning how this interacts with permissions would be a good
> idea too. Given how operations use the view's owner to recurse, that's
> not obvious. Should also explain what permissions are required to do the
> operation on the view.

Added a description about permissions into the documentation.

> 
> 
> > @@ -86,15 +92,17 @@ RangeVarCallbackForLockTable(const RangeVar *rv, Oid relid, Oid oldrelid,
> >          return;                    /* woops, concurrently dropped; no permissions
> >                                   * check */
> >  
> > -    /* Currently, we only allow plain tables to be locked */
> > -    if (relkind != RELKIND_RELATION && relkind != RELKIND_PARTITIONED_TABLE)
> > +
> 
> This newline looks spurious to me.

Removed.

> 
> 
> >  /*
> > + * Apply LOCK TABLE recursively over a view
> > + *
> > + * All tables and views appearing in the view definition query are locked
> > + * recursively with the same lock mode.
> > + */
> > +
> > +typedef struct
> > +{
> > +    Oid root_reloid;
> > +    LOCKMODE lockmode;
> > +    bool nowait;
> > +    Oid viewowner;
> > +    Oid viewoid;
> > +} LockViewRecurse_context;
> 
> Probably wouldn't hurt to pgindent the larger changes in the patch.
> 
> 
> > +static bool
> > +LockViewRecurse_walker(Node *node, LockViewRecurse_context *context)
> > +{
> > +    if (node == NULL)
> > +        return false;
> > +
> > +    if (IsA(node, Query))
> > +    {
> > +        Query        *query = (Query *) node;
> > +        ListCell    *rtable;
> > +
> > +        foreach(rtable, query->rtable)
> > +        {
> > +            RangeTblEntry    *rte = lfirst(rtable);
> > +            AclResult         aclresult;
> > +
> > +            Oid relid = rte->relid;
> > +            char relkind = rte->relkind;
> > +            char *relname = get_rel_name(relid);
> > +
> > +            /* The OLD and NEW placeholder entries in the view's rtable are skipped. */
> > +            if (relid == context->viewoid &&
> > +                (!strcmp(rte->eref->aliasname, "old") || !strcmp(rte->eref->aliasname, "new")))
> > +                continue;
> > +
> > +            /* Currently, we only allow plain tables or views to be locked. */
> > +            if (relkind != RELKIND_RELATION && relkind != RELKIND_PARTITIONED_TABLE &&
> > +                relkind != RELKIND_VIEW)
> > +                continue;
> > +
> > +            /* Check infinite recursion in the view definition. */
> > +            if (relid == context->root_reloid)
> > +                ereport(ERROR,
> > +                        (errcode(ERRCODE_INVALID_OBJECT_DEFINITION),
> > +                        errmsg("infinite recursion detected in rules for relation \"%s\"",
> > +                                get_rel_name(context->root_reloid))));
> 
> Hm, how can that happen? And if it can happen, why can it only happen
> with the root relation?

For example, the following queries cause the infinite recursion of views. 
This is detected and the error is raised.

 create table t (i int);
 create view v1 as select 1;
 create view v2 as select * from v1;
 create or replace view v1 as select * from v2;
 begin;
 lock v1;
 abort;

However, I found that the previous patch could not handle the following
situation in which the root relation itself doesn't have infinite recursion.

 create view v3 as select * from v1;
 begin;
 lock v3;
 abort;

This fixed in the attached patch.

Regards,

> 
> Greetings,
> 
> Andres Freund


-- 
Yugo Nagata <nagata@sraoss.co.jp>