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Fix database locked errors (#3153)

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* Make read-only operations use WithReadTxn
* Allow one database write thread
* Add unit test for concurrent transactions
* Perform some actions after commit to release txn
* Suppress some errors from cancelled context
This commit is contained in:
WithoutPants
2022-11-21 06:49:10 +11:00
committed by GitHub
parent 420c6fa9d7
commit f39fa416a9
54 changed files with 626 additions and 311 deletions
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49
pkg/txn/transaction.go
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@@ -6,7 +6,7 @@ import (
)
type Manager interface {
Begin(ctx context.Context) (context.Context, error)
Begin(ctx context.Context, exclusive bool) (context.Context, error)
Commit(ctx context.Context) error
Rollback(ctx context.Context) error
@@ -17,18 +17,43 @@ type DatabaseProvider interface {
WithDatabase(ctx context.Context) (context.Context, error)
}
type DatabaseProviderManager interface {
DatabaseProvider
Manager
}
type TxnFunc func(ctx context.Context) error
// WithTxn executes fn in a transaction. If fn returns an error then
// the transaction is rolled back. Otherwise it is committed.
// Transaction is exclusive. Only one thread may run a transaction
// using this function at a time. This function will wait until the
// lock is available before executing.
// This function should be used for making changes to the database.
func WithTxn(ctx context.Context, m Manager, fn TxnFunc) error {
const execComplete = true
return withTxn(ctx, m, fn, execComplete)
const (
execComplete = true
exclusive = true
)
return withTxn(ctx, m, fn, exclusive, execComplete)
}
func withTxn(ctx context.Context, m Manager, fn TxnFunc, execCompleteOnLocked bool) error {
// WithReadTxn executes fn in a transaction. If fn returns an error then
// the transaction is rolled back. Otherwise it is committed.
// Transaction is not exclusive and does not enforce read-only restrictions.
// Multiple threads can run transactions using this function concurrently,
// but concurrent writes may result in locked database error.
func WithReadTxn(ctx context.Context, m Manager, fn TxnFunc) error {
const (
execComplete = true
exclusive = false
)
return withTxn(ctx, m, fn, exclusive, execComplete)
}
func withTxn(ctx context.Context, m Manager, fn TxnFunc, exclusive bool, execCompleteOnLocked bool) error {
var err error
ctx, err = begin(ctx, m)
ctx, err = begin(ctx, m, exclusive)
if err != nil {
return err
}
@@ -59,9 +84,9 @@ func withTxn(ctx context.Context, m Manager, fn TxnFunc, execCompleteOnLocked bo
return err
}
func begin(ctx context.Context, m Manager) (context.Context, error) {
func begin(ctx context.Context, m Manager, exclusive bool) (context.Context, error) {
var err error
ctx, err = m.Begin(ctx)
ctx, err = m.Begin(ctx, exclusive)
if err != nil {
return nil, err
}
@@ -102,6 +127,9 @@ func WithDatabase(ctx context.Context, p DatabaseProvider, fn TxnFunc) error {
return fn(ctx)
}
// Retryer is a provides WithTxn function that retries the transaction
// if it fails with a locked database error.
// Transactions are run in exclusive mode.
type Retryer struct {
Manager Manager
// use value < 0 to retry forever
@@ -113,8 +141,11 @@ func (r Retryer) WithTxn(ctx context.Context, fn TxnFunc) error {
var attempt int
var err error
for attempt = 1; attempt <= r.Retries || r.Retries < 0; attempt++ {
const execComplete = false
err = withTxn(ctx, r.Manager, fn, execComplete)
const (
execComplete = false
exclusive = true
)
err = withTxn(ctx, r.Manager, fn, exclusive, execComplete)
if err == nil {
return nil