Berkeley DB 源代码分析（1） --- 代码特征与游标的实现

最新推荐文章于 2019-07-22 16:02:08 发布

david_zhao_wei

最新推荐文章于 2019-07-22 16:02:08 发布

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分类专栏：数据库技术 Berkeley DB 文章标签：代码分析 transactions pointers pair duplicates delete

本文链接：https://blog.youkuaiyun.com/smartpig_zw/article/details/7392264

本文深入分析Berkeley DB源代码，探讨内部如何使用游标连接锁、事务和缓存管理。详细阐述了页面锁定、解锁及从内存池获取、释放页面的过程，并介绍游标调整的事务日志记录，以及键/数据对删除时的逻辑删除和物理删除策略。同时，讨论了离页重复数据（opd）的存储结构和访问方式。

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I. General Notes
1. use a cursor to access db internally. cursor connects lock/txn/logging/AM, etc.
To get a page, first create a cursor if don't have one, then call __db_lget to lock the page, then call __memp_fget to get the page from cache,
then you have the page's pointer. after use, call __TLPUT OR __LPUT to release lock, then call __memp_fput to release page.

2. How to lock/unlock a page and get/put a page from mpool?
See __bam_read_lock.

3. Cursor Ajudgement
Cursor adjustments are logged if they are for subtransactions. This is
because it's possible for a subtransaction to adjust cursors which will
still be active after the subtransaction aborts, and so which must be
restored to their previous locations. Cursors that can be both affected
by our cursor adjustments and active after our transaction aborts can
only be found in our parent transaction -- cursors in other transactions,
including other child transactions of our parent, must have conflicting
locker IDs, and so cannot be affected by adjustments in this transaction.

When an key/data pair is deleted, there can be other cursors pointing to it so
we don't physically delete it immediately, but mark the key/data pair deleted, and mark
all cursors pointing at this k/d with C_DELETED (which is called a