This area is to maintain a compendium of useful information when working with elasticsearch.
Information on how to enable ElasticSearch and perform the initial indexing is kept in https://docs.gitlab.com/ee/integration/elasticsearch.html#enabling-elasticsearch
## Initial installation on OS X
It is recommended to use the Docker image. After installing docker you can immediately spin up an instance with
and use `docker stop elastic55` and `docker start elastic55` to stop/start it.
### Installing on the host
We currently only support Elasticsearch [up to 5.5](https://docs.gitlab.com/ee/integration/elasticsearch.html#requirements), but `brew` only has elasticsearch 6, 5.6, and 2.4 available. While 2.4 would work you probably want to test things out in the latest one we support.
In order to install 5.5.2, you would usually have to hunt down an old homebrew-core commit that contains the recipe for it. We've already done the work for you. Simply run:
this adds `gitlab-elasticsearch-indexer` to `$GOPATH/bin`, please make sure that is in your `$PATH`. After that GitLab will find it and you'll be able to enable it in the admin settings area.
**note:**`make` will not recompile the executable unless you do `make clean` beforehand
## How does it work?
The ElasticSearch integration depends on an external indexer. We ship a [ruby indexer](https://gitlab.com/gitlab-org/gitlab-ee/blob/master/bin/elastic_repo_indexer) by default but are also working on an [indexer written in Go](https://gitlab.com/gitlab-org/gitlab-elasticsearch-indexer). The user must trigger the initial indexing via a rake task, but after this is done GitLab itself will trigger reindexing when required via `after_` callbacks on create, update, and destroy that are inherited from [/ee/app/models/concerns/elastic/application_search.rb](https://gitlab.com/gitlab-org/gitlab-ee/blob/master/ee/app/models/concerns/elastic/application_search.rb).
All indexing after the initial one is done via `ElasticIndexerWorker` (sidekiq jobs).
Search queries are generated by the concerns found in [ee/app/models/concerns/elastic](https://gitlab.com/gitlab-org/gitlab-ee/tree/master/ee/app/models/concerns/elastic). These concerns are also in charge of access control, and have been a historic source of security bugs so please pay close attention to them!
## Existing Analyzers/Tokenizers/Filters
These are all defined in https://gitlab.com/gitlab-org/gitlab-ee/blob/master/ee/lib/elasticsearch/git/model.rb
### Analyzers
#### `path_analyzer`
Used when indexing blobs' paths. Uses the `path_tokenizer` and the `lowercase` and `asciifolding` filters.
Please see the `path_tokenizer` explanation below for an example.
#### `sha_analyzer`
Used in blobs and commits. Uses the `sha_tokenizer` and the `lowercase` and `asciifolding` filters.
Please see the `sha_tokenizer` explanation later below for an example.
#### `code_analyzer`
Used when indexing a blob's filename and content. Uses the `whitespace` tokenizer and the filters: `code`, `edgeNGram_filter`, `lowercase`, and `asciifolding`
The `whitespace` tokenizer was selected in order to have more control over how tokens are split. For example the string `Foo::bar(4)` needs to generate tokens like `Foo` and `bar(4)` in order to be properly searched.
Please see the `code` filter for an explanation on how tokens are split.
#### `code_search_analyzer`
Not directly used for indexing, but rather used to transform a search input. Uses the `whitespace` tokenizer and the `lowercase` and `asciifolding` filters.
### Tokenizers
#### `sha_tokenizer`
This is a custom tokenizer that uses the [`edgeNGram` tokenizer](https://www.elastic.co/guide/en/elasticsearch/reference/5.5/analysis-edgengram-tokenizer.html) to allow SHAs to be searcheable by any sub-set of it (minimum of 5 chars).
example:
`240c29dc7e` becomes:
-`240c2`
-`240c29`
-`240c29d`
-`240c29dc`
-`240c29dc7`
-`240c29dc7e`
#### `path_tokenizer`
This is a custom tokenizer that uses the [`path_hierarchy` tokenizer](https://www.elastic.co/guide/en/elasticsearch/reference/5.5/analysis-pathhierarchy-tokenizer.html) with `reverse: true` in order to allow searches to find paths no matter how much or how little of the path is given as input.
example:
`'/some/path/application.js'` becomes:
-`'/some/path/application.js'`
-`'some/path/application.js'`
-`'path/application.js'`
-`'application.js'`
### Filters
#### `code`
Uses a [Pattern Capture token filter](https://www.elastic.co/guide/en/elasticsearch/reference/5.5/analysis-pattern-capture-tokenfilter.html) to split tokens into more easily searched versions of themselves.
Patterns:
-`"(\\p{Ll}+|\\p{Lu}\\p{Ll}+|\\p{Lu}+)"`: captures CamelCased and lowedCameCased strings as separate tokens
-`'"((?:\\"|[^"]|\\")*)"'`: captures terms inside quotes, removing the quotes
-`"'((?:\\'|[^']|\\')*)'"`: same as above, for single-quotes
-`'\.([^.]+)(?=\.|\s|\Z)'`: separate terms with periods in-between
-`'\/?([^\/]+)(?=\/|\b)'`: separate path terms `like/this/one`
#### `edgeNGram_filter`
Uses an [Edge NGram token filter](https://www.elastic.co/guide/en/elasticsearch/reference/5.5/analysis-edgengram-tokenfilter.html) to allow inputs with only parts of a token to find the token. For example it would turn `glasses` into permutations starting with `gl` and ending with `glasses`, which would allow a search for "`glass`" to find the original token `glasses`
## Gotchas
- 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
