Refactor indexer (#25174)

Refactor `modules/indexer` to make it more maintainable. And it can be
easier to support more features. I'm trying to solve some of issue
searching, this is a precursor to making functional changes.

Current supported engines and the index versions:

| engines | issues | code |
| - | - | - |
| db | Just a wrapper for database queries, doesn't need version | - |
| bleve | The version of index is **2** | The version of index is **6**
|
| elasticsearch | The old index has no version, will be treated as
version **0** in this PR | The version of index is **1** |
| meilisearch | The old index has no version, will be treated as version
**0** in this PR | - |


## Changes

### Split

Splited it into mutiple packages

```text
indexer
├── internal
│   ├── bleve
│   ├── db
│   ├── elasticsearch
│   └── meilisearch
├── code
│   ├── bleve
│   ├── elasticsearch
│   └── internal
└── issues
    ├── bleve
    ├── db
    ├── elasticsearch
    ├── internal
    └── meilisearch
```

- `indexer/interanal`: Internal shared package for indexer.
- `indexer/interanal/[engine]`: Internal shared package for each engine
(bleve/db/elasticsearch/meilisearch).
- `indexer/code`: Implementations for code indexer.
- `indexer/code/internal`: Internal shared package for code indexer.
- `indexer/code/[engine]`: Implementation via each engine for code
indexer.
- `indexer/issues`: Implementations for issues indexer.

### Deduplication

- Combine `Init/Ping/Close` for code indexer and issues indexer.
- ~Combine `issues.indexerHolder` and `code.wrappedIndexer` to
`internal.IndexHolder`.~ Remove it, use dummy indexer instead when the
indexer is not ready.
- Duplicate two copies of creating ES clients.
- Duplicate two copies of `indexerID()`.


### Enhancement

- [x] Support index version for elasticsearch issues indexer, the old
index without version will be treated as version 0.
- [x] Fix spell of `elastic_search/ElasticSearch`, it should be
`Elasticsearch`.
- [x] Improve versioning of ES index. We don't need `Aliases`:
- Gitea does't need aliases for "Zero Downtime" because it never delete
old indexes.
- The old code of issues indexer uses the orignal name to create issue
index, so it's tricky to convert it to an alias.
- [x] Support index version for meilisearch issues indexer, the old
index without version will be treated as version 0.
- [x] Do "ping" only when `Ping` has been called, don't ping
periodically and cache the status.
- [x] Support the context parameter whenever possible.
- [x] Fix outdated example config.
- [x] Give up the requeue logic of issues indexer: When indexing fails,
call Ping to check if it was caused by the engine being unavailable, and
only requeue the task if the engine is unavailable.
- It is fragile and tricky, could cause data losing (It did happen when
I was doing some tests for this PR). And it works for ES only.
- Just always requeue the failed task, if it caused by bad data, it's a
bug of Gitea which should be fixed.

---------

Co-authored-by: Giteabot <teabot@gitea.io>

1 files changed, 3 insertions, 3 deletions

diff --git a/custom/conf/app.example.ini b/custom/conf/app.example.ini
index 13820095ae..760f0440cc 100644
--- a/custom/conf/app.example.ini
+++ b/custom/conf/app.example.ini
@@ -1334,10 +1334,10 @@ LEVEL = Info
 ;; Issue indexer storage path, available when ISSUE_INDEXER_TYPE is bleve
 ;ISSUE_INDEXER_PATH = indexers/issues.bleve ; Relative paths will be made absolute against _`AppWorkPath`_.
 ;;
-;; Issue indexer connection string, available when ISSUE_INDEXER_TYPE is elasticsearch or meilisearch
-;ISSUE_INDEXER_CONN_STR = http://elastic:changeme@localhost:9200
+;; Issue indexer connection string, available when ISSUE_INDEXER_TYPE is elasticsearch (e.g. http://elastic:password@localhost:9200) or meilisearch (e.g. http://:apikey@localhost:7700)
+;ISSUE_INDEXER_CONN_STR =
 ;;
-;; Issue indexer name, available when ISSUE_INDEXER_TYPE is elasticsearch
+;; Issue indexer name, available when ISSUE_INDEXER_TYPE is elasticsearch or meilisearch.
 ;ISSUE_INDEXER_NAME = gitea_issues
 ;;
 ;; Timeout the indexer if it takes longer than this to start.