db: add TestWALFailoverRandomized

Add a randomized test of WAL failover and recovery of a DB from failover WAL
logs.

Close #3865.

Author: jbowens

open_test.go

@@ -7,8 +7,11 @@ package pebble
 import (
 	"bytes"
 	"context"
+	"encoding/binary"
 	"fmt"
 	"io"
+	"math"
+	"math/rand"
 	"os"
 	"path/filepath"
 	"reflect"
@@ -18,12 +21,15 @@ import (
 	"sort"
 	"strconv"
 	"strings"
+	"sync"
 	"sync/atomic"
 	"syscall"
 	"testing"
+	"time"
 
 	"github.com/cockroachdb/datadriven"
 	"github.com/cockroachdb/errors"
+	"github.com/cockroachdb/metamorphic"
 	"github.com/cockroachdb/pebble/internal/base"
 	"github.com/cockroachdb/pebble/internal/cache"
 	"github.com/cockroachdb/pebble/internal/manifest"
@@ -1525,3 +1531,167 @@ func TestMkdirAllAndSyncParents(t *testing.T) {
 		}
 	})
 }
+
+// TestWALFailoverRandomized is a randomzied test exercising recovery in the
+// presence of WAL failover. It repeatedly opens a database, writes a number of
+// batches concurrently and simulates a hard crash using vfs.NewCrashableMem. It
+// ensures that the resulting DB state opens successfully, and the contents of
+// the DB match the expectations based on the keys written.
+//
+// This test is partially a regression test for #3865.
+func TestWALFailoverRandomized(t *testing.T) {
+	seed := time.Now().UnixNano()
+	t.Logf("seed %d", seed)
+	mem := vfs.NewCrashableMem()
+	makeOptions := func(mem *vfs.MemFS) *Options {
+		failoverOpts := WALFailoverOptions{
+			Secondary: wal.Dir{FS: mem, Dirname: "secondary"},
+			FailoverOptions: wal.FailoverOptions{
+				PrimaryDirProbeInterval:      time.Microsecond,
+				HealthyProbeLatencyThreshold: 20 * time.Microsecond,
+				HealthyInterval:              10 * time.Microsecond,
+				UnhealthySamplingInterval:    time.Microsecond,
+				UnhealthyOperationLatencyThreshold: func() (time.Duration, bool) {
+					return 10 * time.Microsecond, true
+				},
+				ElevatedWriteStallThresholdLag: 50 * time.Microsecond,
+			},
+		}
+
+		mean := time.Duration(rand.ExpFloat64() * float64(time.Microsecond))
+		p := rand.Float64()
+		t.Logf("Injecting mean %s of latency with p=%.3f", mean, p)
+		fs := errorfs.Wrap(mem, errorfs.RandomLatency(errorfs.Randomly(p, seed), mean, seed, time.Second))
+		return &Options{
+			FS:                          fs,
+			FormatMajorVersion:          internalFormatNewest,
+			Logger:                      testLogger{t},
+			MemTableSize:                128 << 10, // 128 KiB
+			MemTableStopWritesThreshold: 4,
+			WALFailover:                 &failoverOpts,
+		}
+	}
+
+	// KV state tracking.
+	//
+	// This test uses all uint16 big-endian integers as a keyspace. Values are
+	// randomly sized but always contain the key in the first two bytes. We
+	// track the state of all KVs throughout the test (whether they're
+	// definitely set, maybe set or definitely unset).
+	//
+	// Note that the test may wrap around to the beginning of the keyspace. This
+	// may cause KVs left at kvMaybeSet to be written and be definitively set
+	// the second time around.
+	type kvState int8
+	const (
+		kvUnset    kvState = 0
+		kvMaybeSet kvState = 1
+		kvSet      kvState = 2
+	)
+	const keyspaceSize = math.MaxUint16 + 1
+	var kvs struct {
+		sync.Mutex
+		states   [keyspaceSize]kvState
+		count    uint64 // [0, math.MaxUint16]; INVARIANT: states[count:] all zeroes
+		crashing bool
+	}
+	setIsCrashing := func(crashing bool) {
+		kvs.Lock()
+		defer kvs.Unlock()
+		kvs.crashing = crashing
+	}
+	// transitionState is called by goroutines responsible for committing
+	// batches to the engine. Note that 'i' is the index of the KV before
+	// wrapping around and needs to be modded by math.MaxUint16.
+	transitionState := func(i, count uint64, state kvState) {
+		kvs.Lock()
+		defer kvs.Unlock()
+		if kvs.crashing && state == kvSet {
+			// We're racing with a CrashClone call and it's indeterminate
+			// whether what we think we synced actually made the cut. Leave the
+			// kvs at the kvMaybeSet.
+			state = kvMaybeSet
+		}
+		for j := uint64(0); j < count; j++ {
+			idx := (i + j) % keyspaceSize
+			kvs.states[idx] = max(kvs.states[idx], state)
+		}
+		kvs.count = max(kvs.count, i+count, math.MaxUint16)
+	}
+	// validateState is called on recovery to ensure that engine state agrees
+	// with the tracked KV state.
+	validateState := func(d *DB) {
+		it, err := d.NewIter(nil)
+		require.NoError(t, err)
+		valid := it.First()
+		for i := 0; i < int(kvs.count); i++ {
+			var kvIsSet bool
+			if valid {
+				require.Len(t, it.Key(), 2)
+				require.Equal(t, it.Key(), it.Value()[:2])
+				kvIsSet = binary.BigEndian.Uint16(it.Key()) == uint16(i)
+			}
+			if kvIsSet && kvs.states[i] == kvUnset {
+				t.Fatalf("key %04x is set; state says it should be unset", i)
+			} else if !kvIsSet && kvs.states[i] == kvSet {
+				t.Fatalf("key %04x is unset; state says it should be set", i)
+			}
+			if kvIsSet {
+				valid = it.Next()
+			}
+		}
+		require.NoError(t, it.Close())
+	}
+
+	d, err := Open("primary", makeOptions(mem))
+	require.NoError(t, err)
+	rng := rand.New(rand.NewSource(seed))
+	var wg sync.WaitGroup
+	var n uint64
+	randomOps := metamorphic.Weighted[func()]{
+		{Weight: 1, Item: func() {
+			time.Sleep(time.Microsecond * time.Duration(rand.Intn(30)))
+			t.Log("initiating hard crash")
+			setIsCrashing(true)
+			// Take a crash-consistent clone of the filesystem and use that going forward.
+			mem = mem.CrashClone(vfs.CrashCloneCfg{UnsyncedDataPercent: 50, RNG: rng})
+			wg.Wait() // Wait for outstanding batch commits to finish.
+			_ = d.Close()
+			d, err = Open("primary", makeOptions(mem))
+			require.NoError(t, err)
+			validateState(d)
+			setIsCrashing(false)
+		}},
+		{Weight: 20, Item: func() {
+			count := rng.Intn(14) + 1
+			var k [2]byte
+			var v [4096]byte
+			b := d.NewBatch()
+			for i := 0; i < count; i++ {
+				j := uint16((n + uint64(i)) % keyspaceSize)
+				binary.BigEndian.PutUint16(k[:], j)
+				vn := max(rng.Intn(cap(v)), 2)
+				binary.BigEndian.PutUint16(v[:], j)
+				require.NoError(t, b.Set(k[:], v[:vn], nil))
+			}
+			maybeSync := NoSync
+			if rng.Intn(2) == 1 {
+				maybeSync = Sync
+			}
+			wg.Add(1)
+			go func(n, count uint64) {
+				defer wg.Done()
+				transitionState(n, count, kvMaybeSet)
+				require.NoError(t, b.Commit(maybeSync))
+				if maybeSync == Sync {
+					transitionState(n, count, kvSet)
+				}
+			}(n, uint64(count))
+			n += uint64(count)
+		}},
+	}
+	nextRandomOp := randomOps.RandomDeck(rng)
+	for o := 0; o < 1000; o++ {
+		nextRandomOp()()
+	}
+}