HBase row level transaction lock

Jingguo pot 2020-11-09 16:06:44
hbase row level transaction lock


Write concurrency control :

 Just write ( Or update ) Get the row lock before , If not , Indicates that another thread has taken the lock , You need to keep retrying and waiting or spinning and waiting , Until another thread releases the lock . After you get the lock, you start writing data , After writing, release the row lock . This kind of row lock mechanism is the most commonly used means to achieve write concurrency control , You can see MySQL It also uses row lock to achieve write concurrency .

Write concurrency for batch writes to multiple lines :

HBase Support batch write ( Or batch update ), That is, a thread updates the same Region Multiple lines of records in . Then how to ensure the concurrency control of batch writes in current transaction and batch writes in other transactions ? The idea is still the same , Use row lock . But it should be noted here that the two-phase lock protocol must be used , namely :
(1) Get all the pending writes ( to update ) Row lock of row record
(2) Start writing ( to update ) operation
(3) After the completion of writing, the row locks of all row records are released uniformly
Cannot update a row lock ( Release ) a line , It is easy to form deadlock between multiple transactions . Two phase lock protocol is to avoid deadlock ,MySQL Transaction write concurrency control also uses two-phase lock protocol .

Rowkey info:company info:role
greg cloudera engineer

Rowkey info:company info:role
greg restaurant waiter

Two concurrent write requests come in at the same time , Write a row of data separately . Without concurrency control , There will be a crossover .

Rowkey info:company info:role
greg restaurant engineer

Read write concurrency control :
Business A complete .
Rowkey info:company info:role
greg cloudera engineer

Start executing the transaction B
Rowkey info:company
greg restaurant

Here comes the read request ,info:role Not yet updated .

info:role
waiter

The data read is :
Rowkey info:company info:role
greg restaurant engineer

There is a data inconsistency .

Multi version concurrency control (MVCC Mechanism -Mutil Version Concurrent Control):

Two write transactions are assigned sequence numbers 1 And serial number 2, When the read request comes in 1 Already completed , Business 2 Has yet to be completed , So the allocation transaction 1 The corresponding serial number 1 For reading requests . Now the serial number 1 It can be seen from this reading that , Serial number 2 Not visible for this reading .

+---+---+---+---+---+---+---+---+---+----+----+----+----+
| 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 10 | 11 | 12 | 13 |
+---+---+---+---+---+---+---+---+---+----+----+----+----+

All transactions will generate a region Self increasing sequence of levels .

1、 If the transaction 1 And transaction 2 And transaction 3 It's the same line of operation , Business 1 complete , Business 2 Hang in the air , Business 3 complete . At this point, the read request comes to read the line , Only transactions can be read 1. When a transaction 2 The transaction cannot be read until it is finished 3

2、 If the transaction 1~ Business 12 Different lines of operation , Business 1~ Business 11 It's not finished yet , Business 12 complete , At this point, the read request comes to read the transaction 12 The data of , Still waiting for the transaction 1~ Business 11 The transaction cannot be read until it is finished 12 The content of ,
So what you read is a transaction 12 The transaction content before the corresponding line . Because there is no function to compare the unfinished transaction with the content of the current read request , And a transaction may contain multiple rows . To compare with the current request ,
It will consume more performance .

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本文为[Jingguo pot]所创,转载请带上原文链接,感谢

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