When running geth to sync a full node, what is the meaning of cache and handles?

Question

What does it means:

cache=128 handles=1024

how to change those values?

Answer 1

Just to add to Ismael's answer, even if you were to increase the number of per-process file handles in the OS itself, you'd still be max'd out at 1024.

From flags.go:

// makeDatabaseHandles raises out the number of allowed file handles per process
// for Geth and returns half of the allowance to assign to the database.
func makeDatabaseHandles() int {
    if err := raiseFdLimit(2048); err != nil {
        Fatalf("Failed to raise file descriptor allowance: %v", err)
    }
    limit, err := getFdLimit()
    if err != nil {
        Fatalf("Failed to retrieve file descriptor allowance: %v", err)
    }
    if limit > 2048 { // cap database file descriptors even if more is available
        limit = 2048
    }
    return limit / 2 // Leave half for networking and other stuff
}

To reduce them, you'd have to fiddle about with your OS limits, as per this answer. (Though it assumes you're on Linux.)

Answer 2

From geth --help

--cache value Megabytes of memory allocated to internal caching (min 16MB / database forced) (default: 128)

I see no parameter how to modify handles.