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Diffstat (limited to 'doc/development')
| -rw-r--r-- | doc/development/elasticsearch.md | 43 | ||||
| -rw-r--r-- | doc/development/img/elasticsearch_architecture.svg | 1 |
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diff --git a/doc/development/elasticsearch.md b/doc/development/elasticsearch.md index 635895051bc..090e5235619 100644 --- a/doc/development/elasticsearch.md +++ b/doc/development/elasticsearch.md @@ -148,26 +148,49 @@ Uses an [Edge NGram token filter](https://www.elastic.co/guide/en/elasticsearch/ - Searches can have their own analyzers. Remember to check when editing analyzers - `Character` filters (as opposed to token filters) always replace the original character, so they're not a good choice as they can hinder exact searches -## Architecture +## Zero downtime reindexing with multiple indices -GitLab uses `elasticsearch-rails` for handling communication with Elasticsearch server. However, in order to achieve zero-downtime deployment during schema changes, an extra abstraction layer is built to allow: +Currently GitLab can only handle a single version of setting. Any setting/schema changes would require reindexing everything from scratch. Since reindexing can take a long time, this can cause search functionality downtime. -* Indexing (writes) to multiple indexes, with different mappings -* Switching to different index for searches (reads) on the fly +To avoid downtime, GitLab is working to support multiple indices that +can function at the same time. Whenever the schema changes, the admin +will be able to create a new index and reindex to it, while searches +continue to go to the older, stable index. Any data updates will be +forwarded to both indices. Once the new index is ready, an admin can +mark it active, which will direct all searches to it, and remove the old +index. -Currently we are on the process of migrating models to this new design (e.g. `Snippet`), and it is hardwired to work with a single version for now. +This is also helpful for migrating to new servers, e.g. moving to/from AWS. -Traditionally, `elasticsearch-rails` provides class and instance level `__elasticsearch__` proxy methods. If you call `Issue.__elasticsearch__`, you will get an instance of `Elasticsearch::Model::Proxy::ClassMethodsProxy`, and if you call `Issue.first.__elasticsearch__`, you will get an instance of `Elasticsearch::Model::Proxy::InstanceMethodsProxy`. These proxy objects would talk to Elasticsearch server directly. +Currently we are on the process of migrating to this new design. Everything is hardwired to work with one single version for now. -In the new design, `__elasticsearch__` instead represents one extra layer of proxy. It would keep multiple versions of the actual proxy objects, and it would forward read and write calls to the proxy of the intended version. +### Architecture -The `elasticsearch-rails`'s way of specifying each model's mappings and other settings is to create a module for the model to include. However in the new design, each model would have its own corresponding subclassed proxy object, where the settings reside in. For example, snippet related setting in the past reside in `SnippetsSearch` module, but in the new design would reside in `SnippetClassProxy` (which is a subclass of `Elasticsearch::Model::Proxy::ClassMethodsProxy`). This reduces namespace pollution in model classes. +The traditional setup, provided by `elasticsearch-rails`, is to communicate through its internal proxy classes. Developers would write model-specific logic in a module for the model to include in (e.g. `SnippetsSearch`). The `__elasticsearch__` methods would return a proxy object, e.g.: + +- `Issue.__elasticsearch__` returns an instance of `Elasticsearch::Model::Proxy::ClassMethodsProxy` +- `Issue.first.__elasticsearch__` returns an instance of `Elasticsearch::Model::Proxy::InstanceMethodsProxy`. + +These proxy objects would talk to Elasticsearch server directly (see top half of the diagram). + + + +In the planned new design, each model would have a pair of corresponding subclassed proxy objects, in which model-specific logic is located. For example, `Snippet` would have `SnippetClassProxy` and `SnippetInstanceProxy` (being subclass of `Elasticsearch::Model::Proxy::ClassMethodsProxy` and `Elasticsearch::Model::Proxy::InstanceMethodsProxy`, respectively). + +`__elasticsearch__` would represent another layer of proxy object, keeping track of multiple actual proxy objects. It would forward method calls to the appropriate index. For example: + +- `model.__elasticsearch__.search` would be forwarded to the one stable index, since it is a read operation. +- `model.__elasticsearch__.update_document` would be forwarded to all indices, to keep all indices up-to-date. The global configurations per version are now in the `Elastic::(Version)::Config` class. You can change mappings there. ### Creating new version of schema -Currently GitLab would still work with a single version of setting. Once it is implemented, multiple versions of setting can exists in different folders (e.g. `ee/lib/elastic/v12p1` and `ee/lib/elastic/v12p3`). To keep a continuous git history, the latest version lives under the `/latest` folder, but is aliased as the latest version. +NOTE: **Note:** this is not applicable yet as multiple indices functionality is not fully implemented. + +Folders like `ee/lib/elastic/v12p1` contain snapshots of search logic from different versions. To keep a continuous git history, the latest version lives under `ee/lib/elastic/latest`, but its classes are aliased under an actual version (e.g. `ee/lib/elastic/v12p3`). When referencing these classes, never use the `Latest` namespace directly, but use the actual version (e.g. `V12p3`). + +The version name basically follows GitLab's release version. If setting is changed in 12.3, we will create a new namespace called `V12p3` (p stands for "point"). Raise an issue if there is a need to name a version differently. If the current version is `v12p1`, and we need to create a new version for `v12p3`, the steps are as follows: @@ -176,7 +199,7 @@ If the current version is `v12p1`, and we need to create a new version for `v12p 1. Delete `v12p1` folder 1. Copy the entire folder of `latest` as `v12p1` 1. Change the namespace for files under `v12p1` folder from `Latest` to `V12p1` -1. Make changes to `Latest` as needed +1. Make changes to files under the `latest` folder as needed ## Troubleshooting diff --git a/doc/development/img/elasticsearch_architecture.svg b/doc/development/img/elasticsearch_architecture.svg new file mode 100644 index 00000000000..2f38f9b04ee --- /dev/null +++ b/doc/development/img/elasticsearch_architecture.svg @@ -0,0 +1 @@ +<svg version="1.2" width="210mm" height="297mm" viewBox="0 0 21000 29700" preserveAspectRatio="xMidYMid" fill-rule="evenodd" stroke-width="28.222" stroke-linejoin="round" xmlns="http://www.w3.org/2000/svg"><defs class="ClipPathGroup"><clipPath id="a" clipPathUnits="userSpaceOnUse"><path d="M0 0h21000v29700H0z"/></clipPath></defs><g class="SlideGroup"><g class="Slide" clip-path="url(#a)"><g class="Page"><g class="com.sun.star.drawing.CustomShape"><path class="BoundingBox" fill="none" d="M1975 5575h3051v1651H1975z"/><path fill="#FFF" d="M3500 7200H2000V5600h3000v1600H3500z"/><path fill="none" stroke="#3465A4" stroke-width="50" d="M3500 7200H2000V5600h3000v1600H3500z"/><text class="TextShape"><tspan class="TextParagraph" font-family="Arial, sans-serif" font-size="423" font-weight="400"><tspan class="TextPosition" x="2778" y="6311"><tspan>Snippet</tspan></tspan><tspan class="TextPosition" x="2099" y="6785"><tspan>(ActiveRecord)</tspan></tspan></tspan></text></g><g class="com.sun.star.drawing.CustomShape"><path class="BoundingBox" fill="none" d="M1475 3975h4051v3551H1475z"/><path fill="none" stroke="#3465A4" stroke-width="50" d="M3500 7500H1500V4000h4000v3500H3500z"/><text class="TextShape"><tspan class="TextParagraph" font-family="Arial, sans-serif" font-size="423" font-weight="400"><tspan class="TextPosition" x="1788" y="5048"><tspan>ApplicationSearch</tspan></tspan></tspan></text></g><g class="com.sun.star.drawing.ConnectorShape"><path class="BoundingBox" fill="none" d="M5975 4675h8051v701H5975z"/><path fill="none" stroke="#3465A4" stroke-width="50" d="M6000 5350h4000v-650h4000"/></g><g 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23900h-3100v-2100h6200v2100h-3100z"/><text class="TextShape"><tspan class="TextParagraph" font-family="Arial, sans-serif" font-size="423" font-weight="700"><tspan class="TextPosition" x="13505" y="22431"><tspan fill="#C9211E">V12p2::SnippetInstanceProxy</tspan></tspan></tspan></text></g><g class="com.sun.star.drawing.ConnectorShape"><path class="BoundingBox" fill="none" d="M10975 20025h2451v1401h-2451z"/><path fill="none" stroke="#3465A4" stroke-width="50" d="M11000 21400h1463v-1350h937"/></g><g class="com.sun.star.drawing.ConnectorShape"><path class="BoundingBox" fill="none" d="M10975 21375h2451v1501h-2451z"/><path fill="none" stroke="#3465A4" stroke-width="50" d="M11000 21400h1463v1450h937"/></g><g class="com.sun.star.drawing.TextShape"><path class="BoundingBox" fill="none" d="M900 1600h10697v879H900z"/><text class="TextShape"><tspan class="TextParagraph" font-family="Arial, sans-serif" font-size="564" font-weight="400"><tspan class="TextPosition" x="1150" y="2233"><tspan>Standard elasticsearch-rails setup</tspan></tspan></tspan></text></g><g class="com.sun.star.drawing.TextShape"><path class="BoundingBox" fill="none" d="M900 9300h7683v879H900z"/><text class="TextShape"><tspan class="TextParagraph" font-family="Arial, sans-serif" font-size="564" font-weight="400"><tspan class="TextPosition" x="1150" y="9933"><tspan>GitLab multi-indices setup</tspan></tspan></tspan></text></g><g class="com.sun.star.drawing.TextShape"><path class="BoundingBox" fill="none" d="M3400 21300h4821v1197H3400z"/><text class="TextShape"><tspan class="TextParagraph" font-size="388" font-weight="400"><tspan class="TextPosition" x="4250" y="21840"><tspan fill="gray">(instance method)</tspan></tspan><tspan class="TextPosition" x="3651" y="22264"><tspan font-family="Courier" font-size="423">__elasticsearch__</tspan></tspan></tspan></text></g><g class="com.sun.star.drawing.TextShape"><path class="BoundingBox" fill="none" d="M3380 15400h4821v1197H3380z"/><text class="TextShape"><tspan 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fill="gray">(instance method)</tspan></tspan><tspan class="TextPosition" x="9251" y="7364"><tspan font-family="Courier" font-size="423">__elasticsearch__</tspan></tspan></tspan></text></g><g class="com.sun.star.drawing.CustomShape"><path class="BoundingBox" fill="none" d="M1975 25175h2051v851H1975z"/><path fill="none" stroke="#999" stroke-width="50" d="M3000 26000H2000v-800h2000v800H3000z"/><text class="TextShape"><tspan class="TextParagraph" font-family="Arial, sans-serif" font-size="423" font-weight="400"><tspan class="TextPosition" x="2634" y="25748"><tspan fill="gray">Foo</tspan></tspan></tspan></text></g><g class="com.sun.star.drawing.TextShape"><path class="BoundingBox" fill="none" d="M4400 25200h7101v726H4400z"/><text class="TextShape"><tspan class="TextParagraph" font-family="Arial, sans-serif" font-size="423" font-weight="400"><tspan class="TextPosition" x="4650" y="25710"><tspan>elasticsearch-rails’ internal class</tspan></tspan></tspan></text></g><g 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