On Thu, Jun 20, 2024 at 3:23 AM Dmitry O Litvintsev <litvinse@fnal.gov> wrote:
Hello,
I am in the process of migrating DB to Alma9 host. The databse is rather large - few TBs.
I have run pg_basebackup on Alma9 host and established replication from production to it. The idea is to quickly switch from master to this new host during downtime.
Establishing replication went fine. Source postgresql version is 15.6, destination is 15.7
When I psql into replica I get:
WARNING: database "xxx" has a collation version mismatch DETAIL: The database was created using collation version 2.17, but the operating system provides version 2.34. HINT: Rebuild all objects in this database that use the default collation and run ALTER DATABASE xxx REFRESH COLLATION VERSION, or build PostgreSQL with the right library version.
Looking up the issue the solution seems to be
REINDEX database xxx ALTER DATABASE xxx REFRESH COLLATION VERSION
But this defeats the whole idea of having short downtime because REINDEX will take forever.
What is this "or build PostgreSQL with the right library version"? Is this about 15.7 vs 15.6 or is it about different glibc version between RH7 and Alma9?
Is there a better way to handle it? I cannot afford long downtime.
You "only" need to REINDEX indices with TEXT (including CHAR and VARCHAR) columns. That may be most of your indices, or very few.
I use this view and query to find such indices:
create or replace view dba.all_indices_types as select tbcl.relnamespace::regnamespace::text||'.'||tbcl.relname as table_name , ndcl.relname as index_name , array_agg(ty.typname order by att.attnum) as index_types from pg_class ndcl inner join pg_index nd on (ndcl.oid = nd.indexrelid and ndcl.relkind = 'i') inner join pg_class tbcl on (nd.indrelid = tbcl.oid and tbcl.relkind = 'r') inner join pg_attribute att on att.attrelid = nd.indexrelid inner join pg_type ty on att.atttypid = ty.oid where tbcl.relnamespace::regnamespace::text != 'pg_catalog' group by tbcl.relnamespace::regnamespace::text||'.'||tbcl.relname , ndcl.relname order by 1, 2;