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| 152 | 152 | 6. Prints a table: unit, stage, result, version id, time. Each unit's full | |
| 153 | 153 | output is kept in `$TMPDIR/g1t-deploy/<unit>.log`. | |
| 154 | 154 | ||
| 155 | + | #### Migrations run while the old code is still live | |
| 156 | + | ||
| 157 | + | Migrations apply before any code, and a stage takes a minute or more, so | |
| 158 | + | for that long the code in production is the old code reading the new | |
| 159 | + | schema. A migration must keep the old code right: | |
| 160 | + | ||
| 161 | + | - **Add, never change meaning.** New tables and columns (with defaults) are | |
| 162 | + | safe. Rewriting what existing rows mean is not: on 2026-10-08, | |
| 163 | + | `billing/0039` turned comped accounts into `custom` terms at 100%, and | |
| 164 | + | for about 40 seconds the old billing code, which knew only `comped`, saw | |
| 165 | + | flagon-io as a free workspace and refused its workflows. | |
| 166 | + | - **Change meaning in two deploys.** First ship code that reads both the old | |
| 167 | + | and the new form (and keeps writing the old one); then, in a later | |
| 168 | + | deploy, the migration that rewrites the rows; then, if you like, code | |
| 169 | + | that drops the old form. | |
| 170 | + | - **Never drop or rename** a column or table the live code reads in the same | |
| 171 | + | deploy that stops reading it. | |
| 172 | + | ||
| 155 | 173 | #### Telling the status page about a deploy | |
| 156 | 174 | ||
| 157 | 175 | Restarts during a deploy can make a part slow for a minute, which the |