Would like you to know that 
If you are using 
Full replay means that it will most likely require more than 3 hours to start producing blocks again. Thus you have got to switch to your backup witness server so you don't miss any blocks. If you do not have a backup server, than just disable your witness server before making an update to 19.12.
After the replay is ready and you start seeing blocks like in the image below you can switch it back on.
To disable your witness run the following commands
Navigate to steem docker folder
cd steem-docker/
Run your cli wallet
./run.sh remote_wallet
Unclock it with your passowrd
unlock "****************"
Run the following command with your witness name and you can use the incorrect public key like in the example below:
update_witness "yuriks2000" "https://steemit.com" "STM1111111111111111111111111111111114T1Anm" {"account_creation_fee":"0.100 STEEM","maximum_block_size":131072,"sbd_interest_rate":0} true
To re-enable your witness
Run the commands above, but instead of using the incorrect key, place the correct public key you generated when setting up a witness. If you forgot how to generate it than you can refresh your memory here: https://steemit.com/steem/@someguy123/your-guide-to-setting-up-a-witness-server-steem-in-a-box-hf19
Instructions how to upgrade to 19.12 by someguy123
Very useful and easy instructions can be found in the link below. Thanks a lot
