Hello,
This is a pg_upgrade known limitation that has been summarized by Greg Sabino Mullane on https://www.endpoint.com/blog/2016/12/07/postgres-statistics-and-pain-of-analyze
this way:
The nominal reason for not copying the data is that the table format may change from version to version. The real reason is that nobody has bothered to write the conversion logic yet, for pg_upgrade could certainly copy the pg_statistics information: the table has not changed for many years.
Regards
Pierre Forstmann
Le 31/03/2021 à 20:15, Virendra Kumar a écrit :
Hello Team,
I was doing an upgrade of one of our PG (9.6.11 to 11.9) database and came across the question that what is reason PostgreSQL is not doing copy of stats and we have to analyze right after upgrade. There are two situations where this will help when we use this DB as our enterprise database:
1. If DB is in magnitude of hundreds of TB and we have to do analyze it might take several hours before we handover this to application services.
2. We are loosing critical information like most common values and most common freqs because these values are populated over time when many-many sessions hit table and queries with different values of a column.
Any input on this is higly appreciated.
Regards,