Migrates schema and tables one-by-one, for moving from a cluster with an older version of CH

clickhouse-old-version-migration.sh

#!/bin/bash

table='...'
database='...'
local='...'  # clickhouse host - name/IP
remote='...' # clickhouse host - name/IP
CH="clickhouse-client"   # you may add auth here 
settings="  
max_insert_threads=20, # tune threads and block sizes if needed
max_threads=20, 
min_insert_block_size_bytes = 536870912, 
min_insert_block_size_rows = 16777216, 
max_insert_block_size = 16777216,
optimize_on_insert=0
"

# need it to create temp table with same structure (suitable for attach)
params=$($CH -h $remote -q "select partition_key,sorting_key,primary_key from system.tables where table='$table' and database = '$database' " -f TSV)
IFS=$'\t' read -r partition_key sorting_key primary_key <<< $params

$CH -h $local \  # get list of source partitions
-q "select distinct partition from system.parts where table='$table' and database = '$database' "

while read -r partition; do
# check that the partition is already copied
  if [ `$CH -h $remote -q " select count() from system.parts table='$table' and database = '$database' and partition='$partition'"` -eq 0 ] ; then
      $CH -n -h $remote -q "
        create temporary table temp as $database.$table engine=MergeTree 
           partition by ($partition_key) primary key ($primary_key)  order by ($sorting_key);
        SYSTEM STOP MERGES temp; 
        set $settings;
        insert into temp select * from remote($local,$database.$table) where _partition='$partition'
        ;
        alter table $database.$table attach partition $partition from temp
  "
  fi
done