Finally got some code working with saving the Primes on a DB. I started by saving as I find the prime and realised that the constant IO activity was slowing the all process down. Next step was multi treading: this is still not 100%. Here is the code so far:

# Python program to calculate prime numbers
import math
import threading
import sqlite3
count = 0
primeList = []
dbname='/home/roberto/primelist.db'
table_name = 'primes'  # name of the table to be created
new_field = 'prime' # name of the column
field_type = 'INTEGER'  # column data type

def save_primes(number,  topnum):
    while True:
        add_prime(primeList[number])
        number +=1
        if number == (topnum - 1):
            break
    
    
def createDB():
    # Connecting to the database file
    conn = sqlite3.connect(dbname)
    c = conn.cursor()
    try:
        #c.execute('select prime from primes')
        #primeList = c.fetchall()
         for row in  c.execute('select prime from primes'):
            primeList.append(int(row[0]))
       
    except:
        # Creating a new SQLite table with 1 column
        c.execute('CREATE TABLE {tn} ({nf} {ft})'\
                .format(tn=table_name, nf=new_field, ft=field_type))

    # Committing changes and closing the connection to the database file
    conn.commit()
    conn.close()

def add_prime(prime):

    conn=sqlite3.connect(dbname)
    curs=conn.cursor()

    curs.execute("INSERT INTO primes values((?))", (prime,))

    # commit the changes
    conn.commit()

    conn.close()
    
def isPrime(num):
# prime numbers are greater than 1
    if num > 1:
       # check for factors
       for i in range(len(primeList)):
           if (num % primeList[i]) == 0:
               #print(num,"is not a prime number")
               #print(i,"times",num//i,"is",num)
               break
       else:
           print(num,"is a prime number")
           primeList.append(num)
           #add_prime(num)
           
    # if input number is less than
    # or equal to 1, it is not prime
    else:
       print(num,"is not a prime number")
   

#start
createDB()
if len(primeList) == 0:
    num = 1
    count = 0
else:
    num = primeList[len(primeList)-1]+1
    count = len(primeList)
    
while True:
    isPrime(num)
    num += 1
    #this logic will save the primes async to avoid slow IO
    if (num % math.pow(10, 4))==0:
        t = threading.Thread(target=save_primes, args=(count, len(primeList), ))
        t.start()
        count = len(primeList)
    
    if num == math.pow(10, 101):
        break