There can be minutes between ticks during the Asian session, think M1 chart.
Larger charts, think weekend, market holiday (country and broker specific.)
requires knowledge of when your broker stops and starts (not necessary the same
as the market.)
"Free-of-Holes" Charts -
if open = close ? - MQL4 and MetaTrader 4 -
MQL4 programming forum
There is also a broker dependency; how they filter market ticks to clients. One broker was averaging 50 ticks/min during the early US session. Mine averaged 150, and there was one over 350. Same time, same pair, H1 chart.