django db_index 并发迁移运行吗？

Question

我想添加一个 multi-column index to a postgres 数据库。我有一个非阻塞 SQL 命令来执行此操作，如下所示：

CREATE INDEX CONCURRENTLY shop_product_fields_index ON shop_product (id, ...);

当我将 db_index 添加到我的模型并运行迁移时，它会同时运行还是会阻止写入？在 Django 中是否可以并发迁移？

Answer 1

django 不支持 PostgreSQL 并发索引创建。

这是请求此功能的工单 - https://code.djangoproject.com/ticket/21039

但是，您可以在迁移中手动指定任何自定义 RunSQL 操作 - https://docs.djangoproject.com/en/1.8/ref/migration-operations/#runsql

Answer 2

使用 Django 1.10 迁移，您可以使用 RunSQL 创建并发索引，并通过将 atomic = False 设置为迁移的数据属性使迁移成为非原子的来禁用包装事务：

class Migration(migrations.Migration):
    atomic = False # disable transaction

    dependencies = []

    operations = [
        migrations.RunSQL('CREATE INDEX CONCURRENTLY ...')
    ]

运行SQL：https://docs.djangoproject.com/en/1.10/ref/migration-operations/#runsql
非原子迁移：https://docs.djangoproject.com/en/1.10/howto/writing-migrations/#non-atomic-migrations

Answer 3

按照 tgroshon 对新 django 1.10 所说的去做 +

对于较低版本的 django，我使用更详细的子类化方法取得了成功：

from django.db import migrations, models


class RunNonAtomicSQL(migrations.RunSQL):
    def _run_sql(self, schema_editor, sqls):
        if schema_editor.connection.in_atomic_block:
            schema_editor.atomic.__exit__(None, None, None)
        super(RunNonAtomicSQL, self)._run_sql(schema_editor, sqls)


class Migration(migrations.Migration):
    dependencies = [
    ]

    operations = [

        RunNonAtomicSQL(
            "CREATE INDEX CONCURRENTLY",
        )
    ]

Answer 4

您可以使用 SeparateDatabaseAndState 迁移操作来提供自定义 SQL 命令来创建索引。该操作接受两个操作列表：

state_operations 是应用于 Django 模型状态的操作。它们不影响数据库。
database_operations是应用于数据库的操作。

示例迁移可能如下所示：

from django.db import migrations, models

class Migration(migrations.Migration):
    atomic = False

    dependencies = [
        ('myapp', '0001_initial'),
    ]

    operations = [    
        migrations.SeparateDatabaseAndState(    
            state_operations=[
                # operation generated by `makemigrations` to create an ordinary index
                migrations.AlterField(
                    # ...  
                ),
            ],

            database_operations=[
                # operation to run custom SQL command (check the output of `sqlmigrate`
                # to see the auto-generated SQL, edit as needed)
                migrations.RunSQL(sql='CREATE INDEX CONCURRENTLY ...',
                                  reverse_sql='DROP INDEX ...'),
            ],
        ),
    ]

Answer 5

Django 3.0中有AddIndexConcurrently和RemoveIndexConcurrently：

https://docs.djangoproject.com/en/dev/ref/contrib/postgres/operations/#django.contrib.postgres.operations.AddIndexConcurrently

创建迁移，然后将 migrations.AddIndex 更改为 AddIndexConcurrently。从 django.contrib.postgres.operations.

导入

Answer 6

你可以这样做


import django.contrib.postgres.indexes
from django.db import migrations, models
from django.contrib.postgres.operations import AddIndexConcurrently


class Migration(migrations.Migration):

    atomic = False

    dependencies = [
        ("app_name", "parent_migration"),
    ]

    operations = [
        AddIndexConcurrently(
            model_name="mymodel",
            index=django.contrib.postgres.indexes.GinIndex(
                fields=["field1"],
                name="field1_idx",
            ),
        ),
        AddIndexConcurrently(
            model_name="mymodel",
            index=models.Index(
                fields=["field2"], name="field2_idx"
            ),
        ),
    ]

参考：https://docs.djangoproject.com/en/dev/ref/contrib/postgres/operations/#django.contrib.postgres.operations.AddIndexConcurrently

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