trigger – How to improve Bulk INSERTs in PostgreSQL?

I have thousands of tables need to be migrated and merged from multiple PostgreSQL DBs to a single one(at same machine). I’m trying to improve the performance of the process.
I do all things in a C++ program by means of multi-threads where every thread has its own connections to the source DBs and the destination, but I think we can discuss only at SQL layer instead of C++.

the definitions of the destination tables are very similar with the source.
I’m absolutely sure there is no primary key conflictions within all the data.

Can I do things below?

  1. Disable all triggers;
  2. Unlog the destination tables(ALTER TABLE <table_name> SET UNLOGGED);
  3. Drop all the PKs/Indexes, and re-create them after the process
    completed;

And how to Disable all triggers(not only influence a single session or single table)?

This is the definition of the core table, and others very similary.

CREATE TABLE tab_name(
  tick_time TIMESTAMPTZ(6)   NOT NULL,            
  nano_secs INT2             NOT NULL DEFAULT 0,  
  trade_day DATE             NOT NULL,            
  other data,
PRIMARY KEY ( tick_time, nano_secs ) );

CREATE INDEX idx_tab_name_trade_day ON tab_name(trade_day);

And this is the core SQL statement that do the merging:

INSERT INTO public.tab_name( fields list )
SELECT <fields list> FROM source1.tab_name;