It might be long, but it was meant for memorisation originally as it is written following the letters of the Hebrew alphabet. Each verse of a paragraph follows the same letter, each paragraph moving on to the next letter. And it can be learnt in English too. William Wilberforce (he of abolishing slavery fame) memorised it and walked the 20 minutes home from Parliament, through Hyde Park, reciting it. In 1819 he wrote in his journal: "Walked from Hyde Park Corner repeating the 119th psalm in great comfort."
Here's a bit of it:
33 Teach me your decrees, O Lord;
I will keep them to the end.
34 Give me understanding and I will obey your instructions;
I will put them into practice with all my heart.
35 Make me walk along the path of your commands,
for that is where my happiness is found.
36 Give me an eagerness for your laws
rather than a love for money!
37 Turn my eyes from worthless things,
and give me life through your word.
38 Reassure me of your promise,
made to those who fear you.
39 Help me abandon my shameful ways;
for your regulations are good.
40 I long to obey your commandments!
Renew my life with your goodness.