从show innodb status看XtraDB的增强特性

XtraDB存储引擎相对于标准的InnoDB引擎做了很多的改进，从show innodb status的结果可以初步看到部分增强的特性。下面是一个XtraDB测试环境(Linux)的结果：

root@(none) 11:25:18>show innodb status\G
*************************** 1. row ***************************
  Type: InnoDB
  Name:
Status:
=====================================
091106 11:26:11 INNODB MONITOR OUTPUT
=====================================
Per second averages calculated from the last 53 seconds
----------
BACKGROUND THREAD
----------
srv_master_thread loops: 8 1_second, 8 sleeps, 0 10_second, 15 background, 15 flush
srv_master_thread log flush and writes: 8  log writes only: 39
----------
SEMAPHORES
----------
OS WAIT ARRAY INFO: reservation count 9, signal count 9
Mutex spin waits 2, rounds 60, OS waits 0
RW-shared spins 9, OS waits 9; RW-excl spins 0, OS waits 0
Spin rounds per wait: 30.00 mutex, 30.00 RW-shared, 0.00 RW-excl
--------
FILE I/O
--------
I/O thread 0 state: waiting for i/o request (insert buffer thread)
I/O thread 1 state: waiting for i/o request (log thread)
I/O thread 2 state: waiting for i/o request (read thread)
I/O thread 3 state: waiting for i/o request (read thread)
I/O thread 4 state: waiting for i/o request (read thread)
I/O thread 5 state: waiting for i/o request (read thread)
I/O thread 6 state: waiting for i/o request (write thread)
I/O thread 7 state: waiting for i/o request (write thread)
I/O thread 8 state: waiting for i/o request (write thread)
I/O thread 9 state: waiting for i/o request (write thread)
Pending normal aio reads: 0, aio writes: 0,
 ibuf aio reads: 0, log i/o's: 0, sync i/o's: 0
Pending flushes (fsync) log: 0; buffer pool: 0
25 OS file reads, 48 OS file writes, 32 OS fsyncs
0.00 reads/s, 0 avg bytes/read, 0.09 writes/s, 0.08 fsyncs/s
-------------------------------------
INSERT BUFFER AND ADAPTIVE HASH INDEX
-------------------------------------
Ibuf: size 1, free list len 0, seg size 2,
0 inserts, 0 merged recs, 0 merges
Hash table size 553193, node heap has 1 buffer(s)
0.00 hash searches/s, 0.02 non-hash searches/s
---
LOG
---
Log sequence number 48613
Log flushed up to   48613
Last checkpoint at  48613
Max checkpoint age  7782360
Modified age        0
Checkpoint age      0
0 pending log writes, 0 pending chkp writes
24 log i/o's done, 0.04 log i/o's/second
----------------------
BUFFER POOL AND MEMORY
----------------------
Total memory allocated 136806400; in additional pool allocated 0
Internal hash tables (constant factor + variable factor)
    Adaptive hash index 2233316         (2212772 + 20544)
    Page hash           69556
    Dictionary cache    576800  (553912 + 22888)
    File system         41904   (41336 + 568)
    Lock system         167076  (166436 + 640)
    Recovery system     0       (0 + 0)
    Threads             41524   (41348 + 176)
Dictionary memory allocated 22888
Buffer pool size        8191
Buffer pool size, bytes 134201344
Free buffers            8170
Database pages          20
Modified db pages       0
Pending reads 0
Pending writes: LRU 0, flush list 0, single page 0
Pages read 19, created 2, written 45
0.00 reads/s, 0.00 creates/s, 0.04 writes/s
Buffer pool hit rate 1000 / 1000
LRU len: 20, unzip_LRU len: 0
I/O sum[2]:cur[0], unzip sum[0]:cur[0]
--------------
ROW OPERATIONS
--------------
0 queries inside InnoDB, 0 queries in queue
1 read views open inside InnoDB
Main thread process no. 16905, id 2788809632, state: waiting for server activity
Number of rows inserted 4, updated 0, deleted 0, read 0
0.02 inserts/s, 0.00 updates/s, 0.00 deletes/s, 0.00 reads/s
------------
TRANSACTIONS
------------
Trx id counter 509
Purge done for trx's n:o < 506 undo n:o < 0
History list length 1
LIST OF TRANSACTIONS FOR EACH SESSION:
---TRANSACTION 0, not started, process no 16905, OS thread id 2777967520
MySQL thread id 6, query id 196 dxmonitor 172.19.68.250 root
show innodb status
---TRANSACTION 508, ACTIVE 2 sec, process no 16905, OS thread id 2777766816
1 lock struct(s), heap size 320, 0 row lock(s), undo log entries 1
MySQL thread id 7, query id 195 dxmonitor 172.19.68.250 root
TABLE LOCK table `test`.`test` trx id 508 lock mode IX
----------------------------
END OF INNODB MONITOR OUTPUT
============================

1 row in set, 1 warning (0.00 sec)

从上面的结果可以看到：

• 增加了BACKGROUND THREAD部分，显示一些后台线程的统计信息
• SEMAPHORES部分，最后增加了一个关于spin的统计信息。引入了一个新的innodb_spin_wait_delay的参数对spin的行为进行控制
• FILE I/O部分，innodb默认开启4个IO线程，由参数innodb_file_io_threads控制，但在unix/linux平台该参数无效，只能是默认的4个。而XtraDB/innodb plugin默认开启8个IO线程，并且读线程和写线程可以分别由参数innodb_read_io_threads和innodb_write_io_threads控制。在多核CPU环境中，如果CPU和磁盘本身没有成为瓶颈，开启更多线程应该对提升IO性能有很好的作用。而读写线程的单独控制，则可以针对不同应用环境下的要求进行灵活配置。
• LOG部分，增加了max checkpoint age/Modified age/Checkpoint age信息，这些信息可用于调整一些IO相关的参数，具体可参考这里。
• BUFFER POOL AND MEMORY部分，XtraDB更加详细的列出buffer pool中不同部分的详细信息，还有buffer pool的命中率和LRU的信息等，对内存的使用情况一目了然，拒绝黑箱操作。

关于XtraDB的show innodb status的更多改进，请参考这里。