Re: Collation versioning

On Thu, Mar 19, 2020 at 08:12:47PM +0100, Julien Rouhaud wrote:
> On Thu, Mar 19, 2020 at 12:31:54PM +0900, Michael Paquier wrote:
> > On Wed, Mar 18, 2020 at 04:35:43PM +0100, Julien Rouhaud wrote:
> > > On Wed, Mar 18, 2020 at 09:56:40AM +0100, Julien Rouhaud wrote:
> > > AFAICT it was only missing a call to index_update_collation_versions() in
> > > ReindexRelationConcurrently.  I added regression tests to make sure that
> > > REINDEX, REINDEX [INDEX|TABLE] CONCURRENTLY and VACUUM FULL are doing what's
> > > expected.
> > 
> > If you add a call to index_update_collation_versions(), the old and
> > invalid index will use the same refobjversion as the new index, which
> > is the latest collation version of the system, no?  If the operation
> > is interrupted before the invalid index is dropped, then we would keep
> > a confusing value for refobjversion, because the old invalid index
> > does not rely on the new collation version, but on the old one.
> > Hence, it seems to me that it would be correct to have the old invalid
> > index either use an empty version string to say "we don't know"
> > because the index is invalid anyway, or keep a reference to the old
> > collation version intact.  I think that the latter is much more useful
> > for debugging issues when upgrading a subset of indexes if the
> > operation is interrupted for a reason or another.
> 
> Indeed, I confused the _ccold and _ccnew indexes.  So, the root cause is phase
> 4, more precisely the dependency swap in index_concurrently_swap.
> 
> A possible fix would be to teach changeDependenciesOf() to preserve the
> dependency version.  It'd be quite bit costly as this would mean an extra index
> search for each dependency row found.  We could probably skip the lookup if the
> row have a NULL recorded version, as version should either be null or non null
> for both objects.
> 
> I'm wondering if that's a good time to make changeDependenciesOf and
> changeDependenciesOn private, and instead expose a swapDependencies(classid,
> obj1, obj2) that would call both, as preserving the version doesn't really
> makes sense outside a switch.  It's als oa good way to ensure that no CCI is
> performed in the middle.

Hearing no complaints, I implemented that approach in attached v18.

Here's the new behavior for interrupted REINDEX CONCURRENTLY:

# drop table if exists t1;create table t1(id integer, val text); create index on t1(val collate "fr-x-icu");
NOTICE:  00000: table "t1" does not exist, skipping
DROP TABLE
CREATE TABLE
CREATE INDEX

# update pg_depend set refobjversion = 'meh' where refobjversion = '153.97';
UPDATE 1

# select objid::regclass, indisvalid, refobjversion from pg_depend d join pg_index i on i.indexrelid = d.objid where
refobjversionis not null;
 
   objid    | indisvalid | refobjversion
------------+------------+---------------
 t1_val_idx | t          | meh
(1 row)

(on another session: begin; select * from t1 for update;)

# reindex table CONCURRENTLY t1;
^CCancel request sent
ERROR:  57014: canceling statement due to user request

# select objid::regclass, indisvalid, refobjversion from pg_depend d join pg_index i on i.indexrelid = d.objid where
refobjversionis not null;
 
      objid       | indisvalid | refobjversion
------------------+------------+---------------
 t1_val_idx_ccold | f          | meh
 t1_val_idx       | t          | 153.97
(2 rows)

# reindex table CONCURRENTLY t1;
WARNING:  0A000: cannot reindex invalid index "public.t1_val_idx_ccold" concurrently, skipping
WARNING:  XX002: cannot reindex invalid index "pg_toast.pg_toast_16385_index_ccold" concurrently, skipping
REINDEX

# select objid::regclass, indisvalid, refobjversion from pg_depend d join pg_index i on i.indexrelid = d.objid where
refobjversionis not null;
 
      objid       | indisvalid | refobjversion
------------------+------------+---------------
 t1_val_idx_ccold | f          | meh
 t1_val_idx       | t          | 153.97
(2 rows)

# reindex table t1;
WARNING:  0A000: cannot reindex invalid index "pg_toast.pg_toast_16385_index_ccold" on TOAST table, skipping
REINDEX

# select objid::regclass, indisvalid, refobjversion from pg_depend d join pg_index i on i.indexrelid = d.objid where
refobjversionis not null;
 
      objid       | indisvalid | refobjversion
------------------+------------+---------------
 t1_val_idx_ccold | t          | 153.97
 t1_val_idx       | t          | 153.97
(2 rows)


I also rebased the patchset against master (so removing the regcollation
patch), but no other changes otherwise, so there's still the direct updates on
the catalog in the regressoin tests.