til/postgres/inspect-progress-of-long-running-create-index.md

Inspect Progress Of Long-Running Create Index

Strategically applied indexes are an important part of keeping queries against a database fast. Initially applying those indexes—especially for large tables in production—can take a bit of time.

The create index call doesn't provide any indication of progress. So if applying an index takes minutes or even hours, it can be disconcerting.

Is it still working or is it locked up? How far along is it?

Postgres tracks the index creation process in pg_stat_progress_create_index and we can query that table.

select
  now()::time(0), 
  a.query, 
  p.phase, 
  p.blocks_total, 
  p.blocks_done, 
  p.tuples_total, 
  p.tuples_done,
  ai.schemaname,
  ai.relname,
  ai.indexrelname
from pg_stat_progress_create_index p 
join pg_stat_activity a on p.pid = a.pid
left join pg_stat_all_indexes ai on ai.relid = p.relid and ai.indexrelid = p.index_relid;

There are a bunch of phases that Postgres goes through to create the index, especially if it is being created concurrently. The blocks_done and tuples_done numbers will keep ticking along, giving you an indication that the process is proceeding.

source one and source two