DOC DB read-only replicas #587
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en/02_Developer_Guides/08_Performance/07_DB_read_only_replicas.md
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| If one or more read-only replicas have been configured, then one of the read-only replicas will be selected from the pool of available replicas to handle queries for the rest of the request cycle. However the primary database will be used instead if one of the follow criteria has been met: | ||
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| - The current query includes any mutable SQL such as `INSERT` or `DELETE`. The primary database will be used for the current query, as well as any future queries, including read queries, for the rest of the current request cycle. Mutable SQL is defined on [`DBConnector::isQueryMutable()`](api:SilverStripe\ORM\Connect\DBConnector::isQueryMutable()). | ||
| - The HTTP request that matched a rule defined in [`Director.must_use_primary_db_rules`](api:SilverStripe\Control\Director->must_use_primary_db_rules). By default the URL paths `Security`, `dev`, and `admin` (if `silverstripe/admin` is installed) are covered by this by default. |
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| - The HTTP request that matched a rule defined in [`Director.must_use_primary_db_rules`](api:SilverStripe\Control\Director->must_use_primary_db_rules). By default the URL paths `Security`, `dev`, and `admin` (if `silverstripe/admin` is installed) are covered by this by default. | |
| - The HTTP request matches a routing rule defined in [`Director.must_use_primary_db_rules`](api:SilverStripe\Control\Director->must_use_primary_db_rules). By default the URL paths `Security/*`, `dev/*`, and `admin/*` (if `silverstripe/admin` is installed) are covered by this by default. |
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Still need to add the /* so it's clear it's any path starting with those - i.e. dev/build is included, not just dev on its own.
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As per silverstripe/silverstripe-framework#11379 (comment) $dataQuery->execute() now works a little differently to $dataQuery->query()->execute() - that needs to be called out.
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Also need to explicitly point out that DB::get_conn() will give you a replica by default if you have one configured, unless you explicitly pass in DB::CONN_PRIMARY.
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Re the first point, it's a pretty nuanced detail which is already mentioned in the docs, though not the changelog (which does refer to the docs for more detail)
Note that the withCorrectDatabase() call which $dataQuery->execute() makes which $dataQuery->query()->execute() doesn't simply means it respects DataObject.must_use_primary_db config
From docs:
For any query that goes through a call to DataQuery::execute(), the DataObject subclass being queried is configured with DataObject.must_use_primary_db set to true. This includes most commonly used ORM methods such as DataObject::get(), and excludes SQLSelect methods. By default all core security related DataObject subclasses have must_use_primary_db set to true.
A number of DataQuery methods now use withCorrectDatabase() e.g. DataQuery::count()
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Re the first point, it's a pretty nuanced detail which is already mentioned in the docs, though not the changelog (which does refer to the docs for more detail)
I think it should be explicitly called out in the changelog, since it's a change in behaviour that some people may need to update their code to account for.
| If one or more read-only replicas have been configured, then one of the read-only replicas will be selected from the pool of available replicas to handle queries for the rest of the request cycle. However the primary database will be used instead if one of the follow criteria has been met: | ||
|
|
||
| - The current query includes any mutable SQL such as `INSERT` or `DELETE`. The primary database will be used for the current query, as well as any future queries, including read queries, for the rest of the current request cycle. Mutable SQL is defined on [`DBConnector::isQueryMutable()`](api:SilverStripe\ORM\Connect\DBConnector::isQueryMutable()). | ||
| - The HTTP request that matched a rule defined in [`Director.must_use_primary_db_rules`](api:SilverStripe\Control\Director->must_use_primary_db_rules). By default the URL paths `Security`, `dev`, and `admin` (if `silverstripe/admin` is installed) are covered by this by default. |
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Still need to add the /* so it's clear it's any path starting with those - i.e. dev/build is included, not just dev on its own.
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- DOC DB read-only replicas #587 (comment) still needs to be done
- Added comment to DOC DB read-only replicas #587 (comment) (sorry, forgot to start review)
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Issue silverstripe/silverstripe-framework#11352