The standard names for indexes in PostgreSQL are:
{tablename}_{columnname(s)}_{suffix}
where the suffix is one of the following:
pkeyfor a Primary Key constraint;keyfor a Unique constraint;exclfor an Exclusion constraint;idxfor any other kind of index;fkeyfor a Foreign key;checkfor a Check constraint;
Standard suffix for sequences is
seq for all sequences
Found here
It was found here:
https://stackoverflow.com/questions/4107915/postgresql-default-constraint-names/4108266#4108266
Copied it to gist just in case (if I forget where to look for it)