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Refactor GetNextResourceIndex to make it work properly with transaction (#21469)
Related: * #21362 This PR uses a general and stable method to generate resource index (eg: Issue Index, PR Index) If the code looks good, I can add more tests ps: please skip the diff, only have a look at the new code. It's entirely re-written. Co-authored-by: Lunny Xiao <xiaolunwen@gmail.com>
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wxiaoguang
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commit
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7 changed files with 215 additions and 89 deletions
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@ -8,45 +8,15 @@ import (
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"context"
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"errors"
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"fmt"
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"code.gitea.io/gitea/modules/setting"
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)
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// ResourceIndex represents a resource index which could be used as issue/release and others
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// We can create different tables i.e. issue_index, release_index and etc.
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// We can create different tables i.e. issue_index, release_index, etc.
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type ResourceIndex struct {
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GroupID int64 `xorm:"pk"`
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MaxIndex int64 `xorm:"index"`
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}
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// UpsertResourceIndex the function will not return until it acquires the lock or receives an error.
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func UpsertResourceIndex(ctx context.Context, tableName string, groupID int64) (err error) {
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// An atomic UPSERT operation (INSERT/UPDATE) is the only operation
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// that ensures that the key is actually locked.
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switch {
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case setting.Database.UseSQLite3 || setting.Database.UsePostgreSQL:
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_, err = Exec(ctx, fmt.Sprintf("INSERT INTO %s (group_id, max_index) "+
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"VALUES (?,1) ON CONFLICT (group_id) DO UPDATE SET max_index = %s.max_index+1",
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tableName, tableName), groupID)
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case setting.Database.UseMySQL:
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_, err = Exec(ctx, fmt.Sprintf("INSERT INTO %s (group_id, max_index) "+
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"VALUES (?,1) ON DUPLICATE KEY UPDATE max_index = max_index+1", tableName),
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groupID)
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case setting.Database.UseMSSQL:
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// https://weblogs.sqlteam.com/dang/2009/01/31/upsert-race-condition-with-merge/
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_, err = Exec(ctx, fmt.Sprintf("MERGE %s WITH (HOLDLOCK) as target "+
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"USING (SELECT ? AS group_id) AS src "+
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"ON src.group_id = target.group_id "+
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"WHEN MATCHED THEN UPDATE SET target.max_index = target.max_index+1 "+
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"WHEN NOT MATCHED THEN INSERT (group_id, max_index) "+
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"VALUES (src.group_id, 1);", tableName),
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groupID)
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default:
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return fmt.Errorf("database type not supported")
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}
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return err
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}
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var (
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// ErrResouceOutdated represents an error when request resource outdated
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ErrResouceOutdated = errors.New("resource outdated")
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@ -59,53 +29,85 @@ const (
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MaxDupIndexAttempts = 3
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)
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// GetNextResourceIndex retried 3 times to generate a resource index
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func GetNextResourceIndex(tableName string, groupID int64) (int64, error) {
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for i := 0; i < MaxDupIndexAttempts; i++ {
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idx, err := getNextResourceIndex(tableName, groupID)
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if err == ErrResouceOutdated {
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continue
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}
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if err != nil {
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return 0, err
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}
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return idx, nil
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// SyncMaxResourceIndex sync the max index with the resource
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func SyncMaxResourceIndex(ctx context.Context, tableName string, groupID, maxIndex int64) (err error) {
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e := GetEngine(ctx)
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// try to update the max_index and acquire the write-lock for the record
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res, err := e.Exec(fmt.Sprintf("UPDATE %s SET max_index=? WHERE group_id=? AND max_index<?", tableName), maxIndex, groupID, maxIndex)
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if err != nil {
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return err
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}
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return 0, ErrGetResourceIndexFailed
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affected, err := res.RowsAffected()
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if err != nil {
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return err
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}
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if affected == 0 {
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// if nothing is updated, the record might not exist or might be larger, it's safe to try to insert it again and then check whether the record exists
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_, errIns := e.Exec(fmt.Sprintf("INSERT INTO %s (group_id, max_index) VALUES (?, ?)", tableName), groupID, maxIndex)
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var savedIdx int64
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has, err := e.SQL(fmt.Sprintf("SELECT max_index FROM %s WHERE group_id=?", tableName), groupID).Get(&savedIdx)
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if err != nil {
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return err
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}
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// if the record still doesn't exist, there must be some errors (insert error)
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if !has {
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if errIns == nil {
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return errors.New("impossible error when SyncMaxResourceIndex, insert succeeded but no record is saved")
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}
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return errIns
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}
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}
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return nil
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}
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// DeleteResouceIndex delete resource index
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func DeleteResouceIndex(ctx context.Context, tableName string, groupID int64) error {
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_, err := Exec(ctx, fmt.Sprintf("DELETE FROM %s WHERE group_id=?", tableName), groupID)
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return err
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}
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// GetNextResourceIndex generates a resource index, it must run in the same transaction where the resource is created
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func GetNextResourceIndex(ctx context.Context, tableName string, groupID int64) (int64, error) {
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e := GetEngine(ctx)
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// getNextResourceIndex return the next index
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func getNextResourceIndex(tableName string, groupID int64) (int64, error) {
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ctx, commiter, err := TxContext()
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// try to update the max_index to next value, and acquire the write-lock for the record
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res, err := e.Exec(fmt.Sprintf("UPDATE %s SET max_index=max_index+1 WHERE group_id=?", tableName), groupID)
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if err != nil {
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return 0, err
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}
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defer commiter.Close()
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var preIdx int64
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if _, err := GetEngine(ctx).SQL(fmt.Sprintf("SELECT max_index FROM %s WHERE group_id = ?", tableName), groupID).Get(&preIdx); err != nil {
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affected, err := res.RowsAffected()
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if err != nil {
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return 0, err
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}
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if err := UpsertResourceIndex(ctx, tableName, groupID); err != nil {
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return 0, err
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if affected == 0 {
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// this slow path is only for the first time of creating a resource index
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_, errIns := e.Exec(fmt.Sprintf("INSERT INTO %s (group_id, max_index) VALUES (?, 0)", tableName), groupID)
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res, err = e.Exec(fmt.Sprintf("UPDATE %s SET max_index=max_index+1 WHERE group_id=?", tableName), groupID)
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if err != nil {
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return 0, err
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}
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affected, err = res.RowsAffected()
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if err != nil {
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return 0, err
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}
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// if the update still can not update any records, the record must not exist and there must be some errors (insert error)
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if affected == 0 {
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if errIns == nil {
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return 0, errors.New("impossible error when GetNextResourceIndex, insert and update both succeeded but no record is updated")
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}
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return 0, errIns
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}
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}
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var curIdx int64
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has, err := GetEngine(ctx).SQL(fmt.Sprintf("SELECT max_index FROM %s WHERE group_id = ? AND max_index=?", tableName), groupID, preIdx+1).Get(&curIdx)
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// now, the new index is in database (protected by the transaction and write-lock)
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var newIdx int64
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has, err := e.SQL(fmt.Sprintf("SELECT max_index FROM %s WHERE group_id=?", tableName), groupID).Get(&newIdx)
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if err != nil {
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return 0, err
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}
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if !has {
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return 0, ErrResouceOutdated
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return 0, errors.New("impossible error when GetNextResourceIndex, upsert succeeded but no record can be selected")
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}
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if err := commiter.Commit(); err != nil {
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return 0, err
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}
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return curIdx, nil
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return newIdx, nil
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}
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// DeleteResourceIndex delete resource index
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func DeleteResourceIndex(ctx context.Context, tableName string, groupID int64) error {
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_, err := Exec(ctx, fmt.Sprintf("DELETE FROM %s WHERE group_id=?", tableName), groupID)
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return err
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}
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