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	When using the main branch, I found that some changed code didn't have comments. This PR adds some comments.
		
			
				
	
	
		
			103 lines
		
	
	
		
			3.6 KiB
		
	
	
	
		
			Go
		
	
	
	
	
	
			
		
		
	
	
			103 lines
		
	
	
		
			3.6 KiB
		
	
	
	
		
			Go
		
	
	
	
	
	
// Copyright 2022 The Gitea Authors. All rights reserved.
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// SPDX-License-Identifier: MIT
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package dbfs
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import (
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	"context"
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	"os"
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	"code.gitea.io/gitea/models/db"
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)
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/*
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The reasons behind the DBFS (database-filesystem) package:
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When a Gitea action is running, the Gitea action server should collect and store all the logs.
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The requirements are:
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* The running logs must be stored across the cluster if the Gitea servers are deployed as a cluster.
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* The logs will be archived to Object Storage (S3/MinIO, etc.) after a period of time.
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* The Gitea action UI should be able to render the running logs and the archived logs.
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Some possible solutions for the running logs:
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* [Not ideal] Using local temp file: it can not be shared across the cluster.
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* [Not ideal] Using shared file in the filesystem of git repository: although at the moment, the Gitea cluster's
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	git repositories must be stored in a shared filesystem, in the future, Gitea may need a dedicated Git Service Server
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	to decouple the shared filesystem. Then the action logs will become a blocker.
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* [Not ideal] Record the logs in a database table line by line: it has a couple of problems:
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	- It's difficult to make multiple increasing sequence (log line number) for different databases.
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	- The database table will have a lot of rows and be affected by the big-table performance problem.
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	- It's difficult to load logs by using the same interface as other storages.
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  - It's difficult to calculate the size of the logs.
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The DBFS solution:
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* It can be used in a cluster.
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* It can share the same interface (Read/Write/Seek) as other storages.
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* It's very friendly to database because it only needs to store much fewer rows than the log-line solution.
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* In the future, when Gitea action needs to limit the log size (other CI/CD services also do so), it's easier to calculate the log file size.
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* Even sometimes the UI needs to render the tailing lines, the tailing lines can be found be counting the "\n" from the end of the file by seek.
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  The seeking and finding is not the fastest way, but it's still acceptable and won't affect the performance too much.
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*/
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type dbfsMeta struct {
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	ID              int64  `xorm:"pk autoincr"`
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	FullPath        string `xorm:"VARCHAR(500) UNIQUE NOT NULL"`
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	BlockSize       int64  `xorm:"BIGINT NOT NULL"`
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	FileSize        int64  `xorm:"BIGINT NOT NULL"`
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	CreateTimestamp int64  `xorm:"BIGINT NOT NULL"`
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	ModifyTimestamp int64  `xorm:"BIGINT NOT NULL"`
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}
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type dbfsData struct {
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	ID         int64  `xorm:"pk autoincr"`
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	Revision   int64  `xorm:"BIGINT NOT NULL"`
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	MetaID     int64  `xorm:"BIGINT index(meta_offset) NOT NULL"`
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	BlobOffset int64  `xorm:"BIGINT index(meta_offset) NOT NULL"`
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	BlobSize   int64  `xorm:"BIGINT NOT NULL"`
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	BlobData   []byte `xorm:"BLOB NOT NULL"`
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}
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func init() {
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	db.RegisterModel(new(dbfsMeta))
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	db.RegisterModel(new(dbfsData))
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}
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func OpenFile(ctx context.Context, name string, flag int) (File, error) {
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	f, err := newDbFile(ctx, name)
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	if err != nil {
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		return nil, err
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	}
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	err = f.open(flag)
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	if err != nil {
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		_ = f.Close()
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		return nil, err
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	}
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	return f, nil
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}
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func Open(ctx context.Context, name string) (File, error) {
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	return OpenFile(ctx, name, os.O_RDONLY)
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}
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func Create(ctx context.Context, name string) (File, error) {
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	return OpenFile(ctx, name, os.O_RDWR|os.O_CREATE|os.O_TRUNC)
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}
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func Rename(ctx context.Context, oldPath, newPath string) error {
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	f, err := newDbFile(ctx, oldPath)
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	if err != nil {
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		return err
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	}
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	defer f.Close()
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	return f.renameTo(newPath)
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}
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func Remove(ctx context.Context, name string) error {
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	f, err := newDbFile(ctx, name)
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	if err != nil {
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		return err
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	}
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	defer f.Close()
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	return f.delete()
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}
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