class ItemRef(BaseModel): identification_method = models.ForeignKey( 'IdentificationMethod', verbose_name=_("Identification Method"), on_delete=models.CASCADE ) identification_values = JSONField() def __str__(self): return str(self.id) ItemDescription class ItemDescription(BaseModel): ''' Fie...
然后是时间戳。这使得数据库可以首先执行等式，然后搜索最后一个时间戳。它应该是索引中的一个元组。
location_idcharactervarying(10000000)COLLATEpg_catalog."default", query_id uuid,CONSTRAINTbase_image_pkeyPRIMARYKEY (id),CONSTRAINTbase_image_query_id_b2da2903_fk_base_query_pk_idFOREIGNKEY (query_id)REFERENCESpublic.base_query (pk_id)MATCHSIMPLEONUPDATENOACTIONONDELETENOACTION DEFERRABLE INITIALLY ...
然后是时间戳。这使得数据库可以首先执行等式，然后搜索最后一个时间戳。它应该是索引中的一个元组。
当我们更新表的行时(使用 UPDATE 或 DELETE 语句),PostgreSQL 不会简单地覆盖旧行。 相反,PostgreSQL 通过将更新事务的 XID 写入 xmax 字段,将旧行“标记”为“已删除”。在 UPDATE 的情况下(就像 INSERT 一样),创建新行,其 xmin 字段用创建事务的 XID“标记”。These information is stored in “xmin” ...
I have noticed that deletion is almost instantaneous if the data blob is either null or very small (just a few bytes). In fact, it seems that the time it takes to delete is proportional to the amount of data deleted. Deletion is done like DELETE FROM stuff WHERE stuff.id IN ( SELECT...
Improves performance of bulk deletesif the data you're expiring is associated with older partitions, so you can avoid having to scan the table, table bloat, and fragmentation by simply dropping the old partitions. Improves performance of autovacuum, since it can run in parallel on the partitio...
Single key: Your workload is mostly based on a single key, which you just have to create, read, update, and delete. (Therefore the majority of your transactions will only need to go to a single shard in the distributed Citus cluster.) ...
you cannot use the table being changed (update/delete/insert) in a sub-select you cannot create a view that uses a derived table (Possible since MySQL 8.0) create view x as select * from (select * from y); statement level read consistency. Needed for e.g.: update foo set x = y...
In time series workloads, it is common to drop (or delete, or expire) old data once they are not required anymore. Having partitions, it becomes very efficient to drop old data as Postgres does not need to read all the data it drops. To make dropping partitions older than a given th...