Databases
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    <p>Sequel's <code>Dataset#each</code> does yield individual rows at a time, but most database drivers will load the entire result in memory first.</p> <p>If you are using Sequel's Postgres adapter, you can choose to use real cursors:</p> <pre><code>posts.use_cursor.each{|p| puts p} </code></pre> <p>This fetches 1000 rows at a time by default, but you can use an option to specify the amount of rows to grab per cursor fetch:</p> <pre><code>posts.use_cursor(:rows_per_fetch=&gt;100).each{|p| puts p} </code></pre> <p>If you aren't using Sequel's Postgres adapter, you can use Sequel's pagination extension:</p> <pre><code>Sequel.extension :pagination posts.order(:id).each_page(1000){|ds| ds.each{|p| puts p}} </code></pre> <p>However, like ActiveRecord's <code>find_in_batches</code>/<code>find_each</code>, this does separate queries, so you need to be careful if there are concurrent modifications to the dataset you are retrieving.</p> <p>The reason this isn't the default in Sequel is probably the same reason it isn't the default in ActiveRecord, which is that it isn't a good default in the general case. Only queries with large result sets really need to worry about it, and most queries don't return large result sets.</p> <p>At least with the Postgres adapter cursor support, it's fairly easy to make it the default for your model:</p> <pre><code>Post.dataset = Post.dataset.use_cursor </code></pre> <p>For the pagination extension, you can't really do that, but you can wrap it in a method that makes it mostly transparent.</p>
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    1. POAre there any Ruby ORMs which use cursors or smart fetch?
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    1. USthe Tin Man
    1. USJeremy Evans
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    1. POAre there any Ruby ORMs which use cursors or smart fetch?
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    1. CODoes it work also for MySql or is it only with Postgres ?
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      1. USmb14
    2. COThe use_cursor stuff is postgres-only. I'm not sure MySQL supports cursors for returning results. The MySQL cursor documentation states "MySQL supports cursors inside stored programs", see http://dev.mysql.com/doc/refman/5.6/en/cursors.html.
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    3. COPhp use db_fetch massively, so I guess Mysql support cursors. However maybe not in the default ruby driver
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