Cuneiform tablets make up the largest source of older writings. Millions might be a stretch, since the only numbers I could find added up to 500K tablets, and tablets ≠ texts.

The Dead Sea Scrolls are dated to ~200BC-AD100, which appears to be roughly contemporaneous with the oldest extant Chinese manuscript fragments.

Note that this is assuming that you're counting the dates of the manuscripts themselves, not the dates of texts being composed. There's a lot of texts in Greek and Latin known to be older, but they are known only from fourth- or fifth-hand copies in manuscripts dating back usually to later than AD600.

> tablets ≠ texts

C'mon now. Sumerian tablets are documents, we're not talking about ticket stubs.

Here's some long form examples:

https://en.wikipedia.org/wiki/Gudea_cylinders

>The Gudea cylinders are a pair of terracotta cylinders dating to circa 2125 BC, on which is written in cuneiform a Sumerian myth called the Building of Ningursu's temple.[1] The cylinders were made by Gudea, the ruler of Lagash, and were found in 1877 during excavations at Telloh (ancient Girsu), Iraq and are now displayed in the Louvre in Paris, France. They are the largest cuneiform cylinders yet discovered and contain the longest known text written in the Sumerian language.

> C'mon now. Sumerian tablets are documents, we're not talking about ticket stubs.

Oh, I know. I was just making reference to the fact that something like the Epic of Gilgamesh might be on several tablets.