If Saarlaccs take a thousand years to digest a meal, how did Jabba the Hutt know that HIS Saarlacc was even READY to eat something again? His most recent meal might have been only 500 years ago. How would Jabba even know when the Saarlacc ate last?
How long do Hutts live (provided they don’t die in an autoerotic asphyxiation accident)?
Hmm.
To quote Harrison Ford (speaking to Mark Hamill, as I recall):
“Kid, this ain’t that kinda movie.”
Somebody shoulda told Carrie Fisher that.
IDK but the saarlacc was pretty darn big. Maybe it was just ready for another bite? Seriously though, most animals are not finished digesting when they eat again. There are generally a few different stages and organs that the meal travels through before absorption is complete and the waste excreted.
What I want to know is: Does a saarlacc come out of its hole to poop? If not, is it just sitting in two thousand years of excreta?
On the other hand, Hutts are another of the long-lived races in the Star Wars universe. Sources say Jabba was 604 when he was killed and could expect to live double that or more, irritated, bikini-clad princesses notwithstanding.
There is some speculation that a sarlacc is a plant rather than an animal. See here for more than you ever cared to know.
The Hutts have great accountants.
The prisoners were probably the equivalent of an after-dinner mint to the Saarlacc. Compared to its capacity, they were negligible.
This. Saarlaccs are always hungry. Asking, “Ya ready t’ eat?” just wastes time.
It could one of the many creatures that kills even when it’s not hungry. Also, this could explain why Boba Fett survived the Sarlac. It attacked him like a cat attacking a mouse, but didn’t bother to try to eat him.
More than you ever wanted to know about Hutt physiology (though most of it from the now-considered-to-probably-not-be-canon Expanded Universe) is on Wookieepedia.
A few highlights:
Maybe it digests that slowly precisely because it doesn’t know when its next meal will be: When food is plentiful, it eats all it can, and then stores it for up to a millennium to be available for whenever it needs the Calories.
Other things I’ve thought of with regard to this: what difference does it make how long it takes to digest the victim if the victim is dead within a few days from thirst or lack of food, or suffocation from being inside an animal. Also, I find years meaningless in the Star Wars universe unless there’s some sort of “standard year” that the entire galaxy adheres to. I mean, 1,000 years on Tatooine might only be 6 Earth months if it orbits its sun fast enough.
Welcome to the minutiae that Star Wars fans and authors have totally thought of to death. 
(Though, as with my earlier post about Hutts, a lot of that minutiae falls into what used to be called “Expanded Universe” canon, which all essentially became non-canon when Disney bought Lucasfilm.)
Yes, there’s a Galactic Standard Calendar. In it, a standard galactic year is 368 days long, and each day is 24 hours long.
And, the Sarlaac’s digestive system kept its victims alive as it slowly digested them:
This is one of the better speculations I’ve seen so far.
I wanted to say the fat storage is the normal mechanism for this, but then again, there aren’t a lot of fat spiders, and they do something similar, just outside of their bodies.