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pgkeyvalue.go
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pgkeyvalue.go
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package pgkeyvalue
import (
"context"
"fmt"
"strings"
"time"
lru "github.com/hashicorp/golang-lru"
"github.com/jackc/pgconn"
"github.com/jackc/pgerrcode"
"github.com/jackc/pgx/v4"
"github.com/jackc/pgx/v4/pgxpool"
"github.com/pkg/errors"
"github.com/sirupsen/logrus"
"github.com/armadaproject/armada/internal/common/armadaerrors"
"github.com/armadaproject/armada/internal/common/logging"
)
type KeyValue struct {
Key string
Value []byte
}
// PGKeyValueStore is a time-limited key-value store backed by postgres with a local LRU cache.
// The store is write-only, i.e., writing to an existing key will return an error (of type *armadaerrors.ErrAlreadyExists).
// Keys can only be deleted by running the cleanup function.
// Deleting keys does not cause caches to update, i.e., nodes may have an inconsistent view if keys are deleted.
type PGKeyValueStore struct {
// For performance, keys are cached locally.
cache *lru.Cache
// Postgres connection.
db *pgxpool.Pool
// Name of the postgres table used for storage.
tableName string
Logger *logrus.Logger
}
func New(db *pgxpool.Pool, cacheSize int, tableName string) (*PGKeyValueStore, error) {
if db == nil {
return nil, errors.WithStack(&armadaerrors.ErrInvalidArgument{
Name: "db",
Value: db,
Message: "db must be non-nil",
})
}
if tableName == "" {
return nil, errors.WithStack(&armadaerrors.ErrInvalidArgument{
Name: "TableName",
Value: tableName,
Message: "TableName must be non-empty",
})
}
cache, err := lru.New(cacheSize)
if err != nil {
return nil, errors.WithStack(err)
}
return &PGKeyValueStore{
cache: cache,
db: db,
tableName: tableName,
}, nil
}
// Add adds a key-value pair. Returns true if successful and false if the key already exists.
// The postgres table backing the key-value storage is created automatically if it doesn't already exist.
func (c *PGKeyValueStore) Add(ctx context.Context, key string, value []byte) (bool, error) {
ok, err := c.add(ctx, key, value)
// If the table doesn't exist, create it and try again.
var pgErr *pgconn.PgError
if errors.As(err, &pgErr) && pgErr.Code == pgerrcode.UndefinedTable { // Relation doesn't exist; create it.
if err := c.createTable(ctx); err != nil {
return false, errors.WithStack(err)
}
ok, err = c.add(ctx, key, value)
}
return ok, err
}
// LoadOrStoreBatch returns the existing values for the supplied keys if present. Otherwise, it stores and returns
// the supplied value.
// The postgres table backing the key-value storage is created automatically if it doesn't already exist.
func (c *PGKeyValueStore) LoadOrStoreBatch(ctx context.Context, batch []*KeyValue) (map[string][]byte, error) {
ret, err := c.addBatch(ctx, batch)
// If the table doesn't exist, create it and try again.
var pgErr *pgconn.PgError
if errors.As(err, &pgErr) && pgErr.Code == pgerrcode.UndefinedTable { // Relation doesn't exist; create it.
if err := c.createTable(ctx); err != nil {
return nil, errors.WithStack(err)
}
ret, err = c.addBatch(ctx, batch)
}
return ret, err
}
// AddKey is equivalent to Add(ctx, key, nil).
func (c *PGKeyValueStore) AddKey(ctx context.Context, key string) (bool, error) {
return c.Add(ctx, key, nil)
}
func (c *PGKeyValueStore) createTable(ctx context.Context) error {
var pgErr *pgconn.PgError
_, err := c.db.Exec(ctx, fmt.Sprintf("create table %s (key text primary key, value bytea, inserted timestamp not null);", c.tableName))
if errors.As(err, &pgErr) && pgErr.Code == pgerrcode.DuplicateTable { // Someone else just created it, which is fine.
return nil
}
return err
}
func (c *PGKeyValueStore) addBatch(ctx context.Context, batch []*KeyValue) (map[string][]byte, error) {
addedByKey := map[string][]byte{}
keysToAdd := map[string][]byte{}
// first check the cache to see if we have added anything
for _, kv := range batch {
if val, ok := c.cache.Get(kv.Key); ok {
addedByKey[kv.Key] = val.([]byte)
} else {
keysToAdd[kv.Key] = kv.Value
}
}
if len(addedByKey) == len(batch) {
return addedByKey, nil
}
valueStrings := make([]string, 0, len(batch))
valueArgs := make([]interface{}, 0, len(batch)*3)
i := 0
now := time.Now().UTC()
for k, v := range keysToAdd {
valueStrings = append(valueStrings, fmt.Sprintf("($%d, $%d, $%d)", i*3+1, i*3+2, i*3+3))
valueArgs = append(valueArgs, k)
valueArgs = append(valueArgs, v)
valueArgs = append(valueArgs, now)
i++
}
stmt := fmt.Sprintf(
"INSERT INTO %s (key, value, inserted) VALUES %s ON CONFLICT (key) DO UPDATE SET key=EXCLUDED.key RETURNING key, value",
c.tableName,
strings.Join(valueStrings, ","))
rows, err := c.db.Query(ctx, stmt, valueArgs...)
if err != nil {
return nil, errors.WithStack(err)
}
for rows.Next() {
key := ""
var value []byte = nil
err := rows.Scan(&key, &value)
if err != nil {
return nil, errors.WithStack(err)
}
c.cache.Add(key, value)
addedByKey[key] = value
}
return addedByKey, nil
}
func (c *PGKeyValueStore) add(ctx context.Context, key string, value []byte) (bool, error) {
// Overwriting isn't allowed.
if _, ok := c.cache.Get(key); ok {
return false, nil
}
// Otherwise, get and set the key in a transaction.
var exists *bool
err := c.db.BeginTxFunc(ctx, pgx.TxOptions{}, func(tx pgx.Tx) error {
// Check if the key already exists in postgres.
sql := fmt.Sprintf("select exists(select 1 from %s where key=$1) AS \"exists\"", c.tableName)
if err := tx.QueryRow(ctx, sql, key).Scan(&exists); err != nil {
return err
}
// Only write the key-value pair if it doesn't already exist (overwriting not allowed).
if !*exists {
sql = fmt.Sprintf("insert into %s (key, value, inserted) values ($1, $2, now());", c.tableName)
_, err := tx.Exec(ctx, sql, key, value)
if err != nil {
return err
}
}
return nil
})
// We need to return on error (in particular tx rollback)
// to avoid writing to the cache after failing to write to postgres.
if err != nil {
return false, errors.WithStack(err)
}
// Only add to cache if we also wrote to postgres.
if *exists {
return false, nil
} else {
c.cache.Add(key, value)
}
return true, nil
}
// Get returns the value associated with the provided key,
// or &armadaerrors.ErrNotFound if the key can't be found.
func (c *PGKeyValueStore) Get(ctx context.Context, key string) ([]byte, error) {
// First check the local cache.
if value, ok := c.cache.Get(key); ok {
return value.([]byte), nil
}
// Otherwise, check postgres.
var exists bool
var value *[]byte
sql := fmt.Sprintf("select value from %s where key=$1", c.tableName)
err := c.db.QueryRow(ctx, sql, key).Scan(&value)
if errors.Is(err, pgx.ErrNoRows) {
exists = false
} else if err != nil {
return nil, errors.WithStack(err)
} else {
exists = true
}
if !exists {
return nil, errors.WithStack(&armadaerrors.ErrNotFound{
Type: "Postgres key-value pair",
Value: key,
})
}
return *value, nil
}
// Cleanup removes all key-value pairs older than lifespan.
func (c *PGKeyValueStore) Cleanup(ctx context.Context, lifespan time.Duration) error {
sql := fmt.Sprintf("delete from %s where (inserted <= (now() - $1::interval));", c.tableName)
_, err := c.db.Exec(ctx, sql, lifespan)
if err != nil {
return errors.WithStack(err)
}
return nil
}
// PeriodicCleanup starts a goroutine that automatically runs the cleanup job
// every interval until the provided context is cancelled.
func (c *PGKeyValueStore) PeriodicCleanup(ctx context.Context, interval time.Duration, lifespan time.Duration) error {
var log *logrus.Entry
if c.Logger == nil {
log = logrus.StandardLogger().WithField("service", "PGKeyValueStoreCleanup")
} else {
log = c.Logger.WithField("service", "PGKeyValueStoreCleanup")
}
log.Info("service started")
ticker := time.NewTicker(interval)
for {
select {
case <-ctx.Done():
ticker.Stop()
return nil
case <-ticker.C:
start := time.Now()
err := c.Cleanup(ctx, lifespan)
if err != nil {
logging.WithStacktrace(log, err).WithField("delay", time.Since(start)).Warn("cleanup failed")
} else {
log.WithField("delay", time.Since(start)).Info("cleanup succeeded")
}
}
}
}