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reflector.go
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reflector.go
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package reflector
import (
"bytes"
"context"
"database/sql"
"encoding/base64"
"encoding/json"
"fmt"
"io"
"net/url"
"os"
"strings"
"sync/atomic"
"time"
_ "github.com/go-sql-driver/mysql"
"github.com/segmentio/ctlstore"
"github.com/segmentio/ctlstore/pkg/changelog"
"github.com/segmentio/ctlstore/pkg/ctldb"
"github.com/segmentio/ctlstore/pkg/errs"
"github.com/segmentio/ctlstore/pkg/ldb"
"github.com/segmentio/ctlstore/pkg/ldbwriter"
"github.com/segmentio/ctlstore/pkg/ledger"
"github.com/segmentio/ctlstore/pkg/logwriter"
"github.com/segmentio/ctlstore/pkg/sqlite"
"github.com/segmentio/errors-go"
"github.com/segmentio/events/v2"
_ "github.com/segmentio/events/v2/log" // lets events actually log
"github.com/segmentio/stats/v4"
)
// Reflector represents a fully materialized reflector, which polls an
// upstream database's ledger table for DML statements and applies them
// to a local SQLite database (LDB).
type Reflector struct {
shovel func() (*shovel, error)
ldb *sql.DB
logger *events.Logger
upstreamdb *sql.DB
ledgerMonitor *ledger.Monitor
walMonitor starter
stop chan struct{}
}
// UpstreamConfig specifies how to reach and treat the upstream CtlDB.
type UpstreamConfig struct {
Driver string
DSN string
LedgerTable string
QueryBlockSize int
PollInterval time.Duration
PollTimeout time.Duration
PollJitterCoefficient float64
}
// ReflectorConfig is used to configure a Reflector instance that
// is instantiated by ReflectorFromConfig
type ReflectorConfig struct {
LDBPath string
ChangelogPath string
ChangelogSize int
Upstream UpstreamConfig
BootstrapURL string
LedgerHealth ledger.HealthConfig
IsSupervisor bool
LDBWriteCallback ldbwriter.LDBWriteCallback // optional
BootstrapRegion string // optional
// How often to poll the WAL stats
WALPollInterval time.Duration // optional
// Performs a checkpoint after the WAL file exceeds this size in bytes
WALCheckpointThresholdSize int // optional
// What type of checkpoint to perform
WALCheckpointType ldbwriter.CheckpointType // optional
DoMonitorWAL bool // optional
BusyTimeoutMS int // optional
ID string
Logger *events.Logger
}
type DownloadMetric struct {
StartTime int `json:"startTime,omitempty"`
Downloaded string `json:"downloaded"`
Compressed string `json:"compressed"`
}
type starter interface {
Start(ctx context.Context)
}
// Printable returns a "pretty" stringified version of the config
func (c ReflectorConfig) Printable() string {
if len(c.BootstrapURL) > 200 {
c.BootstrapURL = c.BootstrapURL[:200] + "...<truncated>"
}
c.Upstream.DSN = "<REDACTED>"
return fmt.Sprintf("%+v", c)
}
// driverNameSequence will be incremented atomically to ensure unique driver names.
// the database/sql package will panic when registering a driver with the same name
// more than once.
var driverNameSequence int64
// ReflectorFromConfig instantiates a Reflector instance using the
// configuration specified by a ReflectorConfig instance
func ReflectorFromConfig(config ReflectorConfig) (*Reflector, error) {
events.Log("Config: %{config}s", config.Printable())
if config.BootstrapURL != "" {
if _, err := os.Stat(config.LDBPath); err != nil {
switch {
case os.IsNotExist(err):
events.Log("LDB File %{file}s doesn't exist, beginning bootstrap...", config.LDBPath)
err = bootstrapLDB(ldbBootstrapConfig{
url: config.BootstrapURL,
path: config.LDBPath,
restartOnS3NotFound: config.IsSupervisor, // allow supervisor to restart ldb
region: config.BootstrapRegion,
})
if err != nil {
return nil, err
}
default:
return nil, err
}
} else {
events.Log("LDB File %{file}s exists, skipping bootstrap.", config.LDBPath)
}
}
// Allows registering multiple watches (only for testing)
driverName := ldb.LDBDatabaseDriver
// changeBuffer will accumulate statements in the sqlite pre-update hook and then be
// queried in the change log writer.
var changeBuffer sqlite.SQLChangeBuffer
// use a unique driver name to prevent database/sql panics.
driverName = fmt.Sprintf("%s_%d", ldb.LDBDatabaseDriver, atomic.AddInt64(&driverNameSequence, 1))
err := sqlite.RegisterSQLiteWatch(driverName, &changeBuffer)
if err != nil {
return nil, err
}
// Using the WAL journal mode permits high levels of concurrency. If this is
// left as the default, writers and readers will get "database is locked"
// errors if they happen to collide. The reason this is the case is that the
// standard method makes changes in-place on the database file, and keeps an
// undo log. Any readers would see the uncommitted changes, which would
// violate the isolation properties of the database. In WAL mode, the changes
// themselves are appended to the log instead of the database file. After
// the log grows large enough, its contents are "checkpointed" into the
// database file in batch.
var ldbDB *sql.DB
var openErr error
if config.BusyTimeoutMS > 0 {
ldbDB, openErr = sql.Open(driverName, config.LDBPath+fmt.Sprintf("?_journal_mode=wal&_busy_timeout=%d", config.BusyTimeoutMS))
} else {
ldbDB, openErr = sql.Open(driverName, config.LDBPath+"?_journal_mode=wal")
}
if openErr != nil {
return nil, fmt.Errorf("Error when opening LDB at '%v': %v", config.LDBPath, openErr)
}
dsn := config.Upstream.DSN
if config.Upstream.Driver == "mysql" {
dsn, err = ctldb.SetCtldbDSNParameters(dsn)
if err != nil {
return nil, err
}
}
upstreamdb, err := sql.Open(config.Upstream.Driver, dsn)
if err != nil {
return nil, fmt.Errorf("Error when opening upstream DB (%v): %v", config.Upstream.Driver, err)
}
row := upstreamdb.QueryRow("select max(seq) from " + config.Upstream.LedgerTable)
var maxKnownSeq sql.NullInt64
err = row.Scan(&maxKnownSeq)
if err != nil {
return nil, errors.Wrap(err, "find max seq from ledger")
}
events.Log("Max known ledger sequence: %{seq}d", maxKnownSeq)
path := "/var/spool/ctlstore/metrics.json"
err = emitMetricFromFile(path)
if err != nil {
events.Log("Failed to emit metric from file", err)
}
events.Log("Successfully emitted metric from file")
// TODO: check Upstream fields
stop := make(chan struct{})
// This is a function so that initialization can be redone each
// time the shovel operation does a crash-and-restart loop. A good
// example of where this is useful is when the ldbWriter crashes
// due to some kind of invariant violation. In this case, the
// ldbWriter AND the dmlSource is basically useless, since it'll just
// keep trying to repeat the same mistake over and over. Doing this
// as a function allows recovering all the way back to initializing
// the and fetching the last known good sequence in the LDB.
shovel := func() (*shovel, error) {
sqlDBWriter := &ldbwriter.SqlLdbWriter{Db: ldbDB,
ID: config.ID,
Logger: config.Logger,
}
var writer ldbwriter.LDBWriter = sqlDBWriter
var ldbWriteCallbacks []ldbwriter.LDBWriteCallback
useChangelog := config.ChangelogPath != "" && config.ChangelogSize > 0
if useChangelog {
slw := &logwriter.SizedLogWriter{
RotateSize: config.ChangelogSize,
Path: config.ChangelogPath,
FileMode: 0644,
}
clw := &changelog.ChangelogWriter{WriteLine: slw}
ldbWriteCallbacks = append(ldbWriteCallbacks, &ldbwriter.ChangelogCallback{
ChangelogWriter: clw,
})
events.Log("Writing changelog to %{path}s", config.ChangelogPath)
}
if config.LDBWriteCallback != nil {
ldbWriteCallbacks = append(ldbWriteCallbacks, config.LDBWriteCallback)
}
writer = &ldbwriter.CallbackWriter{
DB: ldbDB,
Delegate: writer,
Callbacks: ldbWriteCallbacks,
ChangeBuffer: &changeBuffer,
}
err = ldb.EnsureLdbInitialized(context.TODO(), ldbDB)
if err != nil {
return nil, fmt.Errorf("Error when initializing LDB: %v", err)
}
lastSeq, err := ldb.FetchSeqFromLdb(context.TODO(), ldbDB)
events.Log("Latest seq from %s: %d", config.ID, lastSeq.Int())
if err != nil {
return nil, fmt.Errorf("Error when fetching last sequence from LDB: %v", err)
}
src := &sqlDmlSource{
db: upstreamdb,
lastSequence: lastSeq,
ledgerTableName: config.Upstream.LedgerTable,
queryBlockSize: config.Upstream.QueryBlockSize,
}
return &shovel{
writer: writer,
closers: []io.Closer{sqlDBWriter},
source: src,
pollInterval: config.Upstream.PollInterval,
pollTimeout: config.Upstream.PollTimeout,
jitterCoefficient: config.Upstream.PollJitterCoefficient,
abortOnSeqSkip: true,
maxSeqOnStartup: maxKnownSeq.Int64,
stop: stop,
log: config.Logger,
}, nil
}
ledgerLatencyFunc := ctlstore.NewLDBReaderFromDB(ldbDB).GetLedgerLatency
ledgerMon, err := ledger.NewLedgerMonitor(config.LedgerHealth, ledgerLatencyFunc)
if err != nil {
return nil, errors.Wrap(err, "build ledger latency monitor")
}
var walMon starter
if config.DoMonitorWAL && config.WALPollInterval > 0 {
w := &ldbwriter.SqlLdbWriter{Db: ldbDB}
cper := func() (*ldbwriter.PragmaWALResult, error) {
return w.Checkpoint(config.WALCheckpointType)
}
walMon = NewMonitor(MonitorConfig{
PollInterval: config.WALPollInterval,
Path: config.LDBPath + "-wal",
WALCheckpointThresholdSize: int64(config.WALCheckpointThresholdSize),
}, cper)
} else {
walMon = &noopStarter{}
}
return &Reflector{
shovel: shovel,
ldb: ldbDB,
logger: config.Logger,
upstreamdb: upstreamdb,
ledgerMonitor: ledgerMon,
stop: stop,
walMonitor: walMon,
}, nil
}
func emitMetricFromFile(path string) error {
if _, err := os.Stat(path); err != nil {
switch {
case os.IsNotExist(err):
return nil
default:
return err
}
}
metricsFile, err := os.Open(path)
if err != nil {
return err
}
b, err := io.ReadAll(metricsFile)
if err != nil {
return err
}
var dm DownloadMetric
d := json.NewDecoder(bytes.NewReader(b))
d.DisallowUnknownFields()
err = d.Decode(&dm)
if err != nil {
return err
}
stats.Observe("init_snapshot_download_time", dm.StartTime, stats.T("downloaded", dm.Downloaded), stats.T("compressed", dm.Compressed))
defer func() {
metricsFile.Close()
os.Remove(path)
}()
return nil
}
func (r *Reflector) Start(ctx context.Context) error {
r.logger.Log("Starting Reflector.")
go r.ledgerMonitor.Start(ctx)
go r.walMonitor.Start(ctx)
for {
err := func() error {
shovel, err := r.shovel()
if err != nil {
return errors.Wrap(err, "build shovel")
}
defer shovel.Close()
r.logger.Log("Shoveling...")
stats.Incr("reflector.shovel_start")
err = shovel.Start(ctx)
return errors.Wrap(err, "shovel")
}()
switch {
case errs.IsCanceled(err): // this is normal
case events.IsTermination(errors.Cause(err)): // this is normal
r.logger.Log("Reflector received termination signal")
case err != nil:
switch {
case errors.Is("SkippedSequence", err):
// this is instrumented elsewhere and is not an error that we need
// to handle normally, so we will skip instrumenting this as a
// shovel_error for now.
default:
errs.Incr("reflector.shovel_error")
}
r.logger.Log("Error encountered during shoveling: %{error}+v", err)
}
select {
case <-r.stop:
return nil
case <-ctx.Done():
return ctx.Err()
case <-time.After(1 * time.Second):
// Sleep for a bit here to avoid tight crash looping
}
}
}
func (r *Reflector) Stop() {
close(r.stop)
}
func (r *Reflector) Close() error {
var err error
r.logger.Log("Close() reflector")
err = r.ldb.Close()
if err != nil {
return err
}
err = r.upstreamdb.Close()
if err != nil {
return err
}
// CR: use errors.Join here
return nil
}
// this contains all the info necessary to perform an ldb boostrap
type ldbBootstrapConfig struct {
url string
path string
region string // optional
downloadTo downloadTo // for testing
retryDelay time.Duration // for testing
restartOnS3NotFound bool // whether or not to recreate the ldb if no snapshot exists
}
func bootstrapLDB(cfg ldbBootstrapConfig) error {
shortURL := cfg.url
if len(shortURL) > 256 {
shortURL = shortURL[:256]
}
events.Log("Bootstrap: %{url}s (region:%{region}q) to %{path}s", shortURL, cfg.region, cfg.path)
parsed, err := url.Parse(cfg.url)
if err != nil {
return err
}
scheme := strings.ToLower(parsed.Scheme)
var dler downloadTo
switch {
case cfg.downloadTo != nil:
// allow a test to mock the downloader
dler = cfg.downloadTo
case scheme == "s3":
bucket := parsed.Host
key := parsed.Path
dler = &S3Downloader{
Region: cfg.region,
Bucket: bucket,
Key: key,
StartOverOnNotFound: cfg.restartOnS3NotFound,
}
case scheme == "data":
decoded, err := base64.URLEncoding.DecodeString(parsed.Opaque)
if err != nil {
return err
}
dler = &memoryDownloader{Content: decoded}
default:
return errors.Errorf("unsupported scheme '%s' for bootstrap URL '%s'", scheme, cfg.url)
}
// Download to a temp file first to prevent leaving a zero-byte file
// around, which would trigger the "I already have a file" code paths.
tmpPath := cfg.path + ".tmp"
defer os.RemoveAll(tmpPath)
// make the downloading a function so we can retry it
downloadSnapshot := func() (int64, error) {
f, err := os.OpenFile(tmpPath, os.O_RDWR|os.O_CREATE|os.O_TRUNC, 0644)
if err != nil {
return 0, err
}
defer f.Close()
return dler.DownloadTo(f)
}
incrError := func(typ string) {
errs.Incr("snapshot_download_errors", stats.T("type", typ))
}
// try the download in a loop until is succeeds, retries are done, or some other error happens
maxAttempts := 5
for maxAttempts > 0 {
maxAttempts--
var bytes int64
bytes, err = downloadSnapshot()
switch {
case err == nil:
// success path
err = os.Rename(tmpPath, cfg.path)
if err != nil {
return err
}
events.Log("Bootstrap: Downloaded %{bytes}d bytes", bytes)
return nil
case errors.Is(errs.ErrTypeTemporary, err):
incrError("temporary")
events.Log("Temporary error trying to download snapshot: %{error}s", err)
delay := cfg.retryDelay
if delay == 0 {
delay = time.Second
}
events.Log("Retrying in %{delay}s", delay)
time.Sleep(delay)
case errors.Is(errs.ErrTypePermanent, err):
incrError("permanent")
events.Log("Could not download snapshot: %{error}s", err)
events.Log("Starting with a new LDB")
return nil
default:
incrError("generic")
return err
}
}
return errors.Errorf("download of ldb snapshot failed after max attempts reached: %s", err)
}
type noopStarter struct {
}
func (n *noopStarter) Start(ctx context.Context) {}