ACID in Hbase

Atomicity

1. All mutations are atomic within a row. Any put will either wholely succeed or wholely fail.[3]
1. An operation that returns a "success" code has completely succeeded.
2. An operation that returns a "failure" code has completely failed.
3. An operation that times out may have succeeded and may have failed. However, it will not have partially succeeded or failed.
   粒度：行，对行的操作，返回成功就肯定成功，返回失败就肯定失败，没返回那么要么成功要么失败。（注意batch操作也是适用的）
   那么可以推论：
   • 针对batchput，例如一个batchput里面有两个put, put1: put(row,CF:col,va1), put2:put(row1,CF:col,val2)，要么两个都成功，要么两个都失败。
   • 不保证batchput内针对多行操作时候的原子性。见3.
2. This is true even if the mutation crosses multiple column families within a row.
   粒度：行， 即使一个操作包含了对某行的多个CF的变更，条件1也成立。（那必须是在batch put内）
3. APIs that mutate several rows will _not_ be atomic across the multiple rows. For example, a multiput that operates on rows ‘a‘,‘b‘, and ‘c‘ may return having mutated some but not all of the rows. In such cases, these APIs will return a list of success codes, each of which may be succeeded, failed, or timed out as described above.
   粒度：多行，如1.中所述，batch操作的时候，只能保证粒度为行的原子性，针对某行，返回成功、失败、超时（要么成功要么失败但是不知道）的状态之一
4. The checkAndPut API happens atomically like the typical compareAndSet (CAS) operation found in many hardware architectures.　　
   checkandput就是利用了CAS的原子性，不用这个能用啥
5. The order of mutations is seen to happen in a well-defined order for each row, with no interleaving. For example, if one writer issues the mutation "a=1,b=1,c=1" and another writer issues the mutation "a=2,b=2,c=2", the row must either be "a=1,b=1,c=1" or "a=2,b=2,c=2" and must not be something like "a=1,b=2,c=1".
1. Please note that this is not true _across rows_ for multirow batch mutations.
   粒度：单行、多个batch操作; 多batch操作之间都是排列有序的，不会出现交叉。

Consistency and Isolation

1. All rows returned via any access API will consist of a complete row that existed at some point in the table‘s history.
   通过API访问得到的行，一定是在表的某个timestamp时间点上，完整的一行。
   意思不会在有并发写请求的时候，出现行内、列内不一致的情况。顶多读到的不是最新的。
2. This is true across column families - i.e a get of a full row that occurs concurrent with some mutations 1,2,3,4,5 will return a complete row that existed at some point in time between mutation i and i+1 for some i between 1 and 5.
3. The state of a row will only move forward through the history of edits to it.

Visibility

1. When a client receives a "success" response for any mutation, that mutation is immediately visible to both that client and any client with whom it later communicates through side channels. [3]
2. A row must never exhibit so-called "time-travel" properties. That is to say, if a series of mutations moves a row sequentially through a series of states, any sequence of concurrent reads will return a subsequence of those states.
1. For example, if a row‘s cells are mutated using the "incrementColumnValue" API, a client must never see the value of any cell decrease.
2. This is true regardless of which read API is used to read back the mutation.
3. Any version of a cell that has been returned to a read operation is guaranteed to be durably stored.

Durability

1. All visible data is also durable data. That is to say, a read will never return data that has not been made durable on disk[2]
2. Any operation that returns a "success" code (eg does not throw an exception) will be made durable.[3]
3. Any operation that returns a "failure" code will not be made durable (subject to the Atomicity guarantees above)
4. All reasonable failure scenarios will not affect any of the guarantees of this document.

Tunability

All of the above guarantees must be possible within Apache HBase. For users who would like to trade off some guarantees for performance, HBase may offer several tuning options. For example:

• Visibility may be tuned on a per-read basis to allow stale reads or time travel.
• Durability may be tuned to only flush data to disk on a periodic basis