Data structure corruption caused by snapshot open/close.

[danjacques]

Hey! While working on a downstream project, I traced a problem that I was experiencing back to what I believe is a corruption bug that manifests when using snapshots. I haven't had time to burrow into it yet, but I came away with this fairly minimal reproduction:

package main

import (
        "fmt"

        "github.com/luci/gkvlite"
)

func main() {
        // To trigger: secondKey < firstKey, secondKey < lookup
        firstKey, secondKey, lookup := "c", "a", "b"

        s, _ := gkvlite.NewStore(nil)

        c := s.SetCollection("", nil)
        c.Set([]byte(firstKey), []byte("foo"))

        // If these next two lines don't run, everything works great.
        snap1 := s.Snapshot()
        snap1.Close()

        c.Set([]byte(secondKey), []byte("bar"))
        v, err := c.Get([]byte(lookup))
        fmt.Println(v, err)
}

Prints: [] missing item after item.read() in GetItem()

If the triggering conditions aren't met, if I remove the two snap1 lines, or if I don't close the snapshot, everything works as expected. It looks like there is a corruption of some sort caused by creating and closing snapshots.

I'll take a look deeper tomorrow; just reporting this since now I have a repro.