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    <p>Lots of good advice already.</p> <p>As people have mentioned, if you don't have single point involved, it's simple to just phase in changes by upgrading an app server at a time. But that's rarely the case, so let's ignore that and focus on the difficult bits.</p> <p>Usually there is a db in there which is common to everything else. So that means downtime for the whole system. <em>How do you minimize that?</em></p> <p><strong>Automation</strong>. Script the entire deployment procedure. This (especially) includes any database schema changes. This (especially) includes any data migration you need between versions of the schema.</p> <p><strong>Quality control</strong>. Make sure there are tests. Automated acceptance tests (what the user sees and expects from a business logic / experience perspective). Consider having test accounts in the production system which you can script to test readonly activities. If you don't interact with other external systems, consider doing write activities too. You may need to filter out test account activity in certain parts of the system, especially if they deal with money and accounting. Bean counters get upset, for good reasons, when the beans don't match up.</p> <p><strong>Rehearse</strong>. Deploy in a staging environment which is as identical as possible to production. Do this with production data volumes, and production data. You need to feel how long an alter table takes. And you need to check that an alter table works both structurally, and with all foreign keys in the actual data.</p> <p>If you have massive data volumes, schema changes will take time. Maybe more time than you can afford to be down. One solution is to use <strong>phased data migrations</strong>, so that the schema change is populated with "recent" or "current" (let's say one or three months old) data during the downtime, and the data for the remaining five years can trickle in after you are online again. To the end user things look ok, but some features can't be accessed for another couple of hours/days/whatever.</p>
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A row detail

Detail views are divided into sections. All the information in the data section comes from columns in the selected row. The other sections display data from other, related rows.

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