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首页Onstat快速参考指南:标准与MT命令详解
Onstat快速参考指南:标准与MT命令详解
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更新于2024-07-21
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"《onstat快速参考指南》是一份详尽的Informix onstat命令手册,它按照字母顺序罗列了标准onstat命令(非多线程版本)和多线程(MT)命令。这份指南的结构清晰,每个命令在页面顶部列出其定义,接着是对该命令目的的概要概述,随后是示例输出,以及一个或多个用于解释示例中各个部分的列定义表。 列定义表包括四个栏目:列标题、列描述、格式和相关链接(SeeAlso)。列标题可能包含重要的信息或者需要特别关注的部分,这些部分会以斜体显示。输出格式栏标识了列的输出形式,可能是十六进制(Hex)、十进制(Dec)、浮点数(Flt)、页数(Pages)、字节(Bytes)或字符串(Str)。SeeAlso栏则提供了与当前列相关的其他章节或知识点的引用,帮助用户深入理解和关联不同部分的内容。 例如,如果有一个名为'address'的列,它的含义是在内存中的缓冲区头的地址,输出格式为十六进制。在'address'列的下方,可能会有对其他章节的链接,比如'onstat – gdmp',表明这部分内容与数据缓存管理有关。 这份指南旨在为Informix数据库管理员和开发者提供一个全面的工具,帮助他们迅速查找、理解并执行onstat命令,以便监控和优化系统的性能。无论是进行日常维护还是解决复杂问题,它都是一个宝贵的参考资源。通过阅读这份指南,用户可以掌握如何高效利用onstat命令来获取系统运行状态的深入见解,并根据需要调整和优化数据库的运行环境。"
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The onstat Quick Reference Guide
16
onstat -F Page Flushers (cleaners)
SYNOPSIS
The onstat -F command provides information on what types of buffer pool flushing have
occurred as well as the status of each of the system page cleaner threads.
COLUMN DEFINITIONS
Column Heading Column Description Format See Also
Fg Writes The number of times a foreground write has occurred. This
is caused from the sqlexec thread having to request a flush of
the buffer pool page itself.
Dec
LRU Writes The number of times an LRU write has occurred as
performed by a page cleaner thread.
Dec onstat -R
Chunk Writes The number of times a chunk write has occurred as
performed during a checkpoint.
Dec onstat -m
address The in-memory address of the page cleaner thread. Hex
flusher A sequential number assigned to each of the page cleaner
threads.
Dec
state Describes the current state of the page cleaner thread’s
activity using the following coded values:
C Chunk write
E Exiting
I Idle
L LRU queue write
Str
data Data associated with the state of the page cleaner. If the state
is ‘C’, data is the chunk number, if state is ‘L’, data is the
number of the LRU queue, otherwise data is 0. Data is
displayed in decimal followed by hexadecimal format.
Dec
Hex
NOTES
• onstat -F doesn’t print out as part of the onstat -a command.
• FG writes may occur periodically from a load and do not necessarily indicate a need
for additional page cleaners.
TUNING & MONITORING
Fg Writes LRU Writes Chunk Writes
3 644 26
address flusher state data
a14a444 0 I 0 = 0X0
a14a878 1 I 0 = 0X0
a14acac 2 I 0 = 0X0
a14b0e0 3 I 0 = 0X0
states: Exit Idle Chunk Lru
![](https://csdnimg.cn/release/download_crawler_static/9438537/bg11.jpg)
The onstat Quick Reference Guide
17
In general, foreground writes (FG) should always be zero. A foreground write is caused when a
session needs to have a page from disk placed into the buffer pool, but there are no clean/free
buffers available. In this case, the sqlexec thread will pick a page off the least recently used side of
an LRU queue, write it out, and mark the page as clean. This process is time consuming for a
session and should be avoided.
Whether buffer flushing occurs as part of an LRU write or a Chunk Write should be based on the
nature of the system. LRU writes do not block the system, but are random in nature. Chunk
Writes block the system, but are sequential in nature and tend to be more efficient for large writes.
It is therefore preferable to have LRU writes occuring in a production system for normal
operations and Chunk Writes for loads.
If you are having long checkpoints, onstat -F may provide some insight. While a checkpoint is
occurring, execute onstat -F -r 2. This will show what chunks the page flushers are writing out to
disk every two seconds. By monitoring the data column, it is possible to determine which chunks
are taking the longest to write. If one or more chunks continually have long chunk writes, relative
to the rest of the system, the tables within it might be good candidates for redistribution.
Under normal circumstances, there will be one flusher assigned to each chunk during a
checkpoint.
![](https://csdnimg.cn/release/download_crawler_static/9438537/bg12.jpg)
The onstat Quick Reference Guide
18
onstat -G Global Transaction Identifiers
SYNOPSIS
The onstat -G command provides information on Global Transactions generated through
standard TP/XA calls.
COLUMN DEFINITIONS
DETAIL DEFINITIONS
Column Heading Column Description Format See Also
address In-memory address of the transaction control block Hex
flags Describes the current status of the transaction using a
combination of the following hexadecimal values:
0x00000001 User attached to transaction
0x00000002 Open transaction
0x00000004 Transaction between xa_start() and
xa_end()
0x00000008 Global transaction
0x00000010 Trans marked as abort-only
0x00000020 xaprepare
0x00000040 I-Star prepared
0x00000080 Aborted transaction
0x00000100 Committed transaction
0x00000200 Heuristically completed
0x00000400 begwork log record logged
0x00000800 xa_rollback completed
0x00001000 Started committing drop tab/idx
0x00002000 Started aborting transaction
0x00004000 No undo ops have been performed
0x00008000 Global savepoint active
0x00010000 Savepoint rollback
0x00020000 Cleanup dead transaction
0x00040000 Transaction for a remote server
0x00080000 Transaction entry in use
0x00100000 Transaction has done remote work
0x00200000 RSAM savepoint has begun
0x00400000 TX is I-Star coordinator
0x00800000 TX is I-Star subordinate
0x01000000 TX is long or suspended and has no owner
to signal
0x02000000 Transaction is being recovered
0x04000000 Redo failed for this transaction
0x08000000 Undo failed for this transaction
0x10000000 TX active while I/O failure occurred
0x20000000 TX did some work during recovery
Hex
Global Transaction Identifiers
address flags fID gtl bql data
0 active, 128 total
![](https://csdnimg.cn/release/download_crawler_static/9438537/bg13.jpg)
The onstat Quick Reference Guide
19
Column Heading Column Description Format See Also
0x40000000 TX contains pieces locks
0x80000000 TX did DDR work
fID Format ID for transaction data Dec
gtl Length of the Global Transaction ID Dec
bql Length of the data byte stream for the transaction Dec
data Hexadecimal dump of transaction ID + data Hex
SUMMARY DEFINITIONS
Label Description See Also
active Number of active global transactions
total The current number of transactions that the server has been dynamically allocated to
handle.
NOTES
• A value of –1 in format ID (fID) means the transaction ID (xid) is null.
![](https://csdnimg.cn/release/download_crawler_static/9438537/bg14.jpg)
The onstat Quick Reference Guide
20
onstat -h Buffer Hash Chain Length Histogram
SYNOPSIS
The onstat -h command provides information on the buffer header hash chain used to access
pages in the buffer pool.
COLUMN DEFINITIONS
Column Heading Column Description Format See Also
# of chains A count of the number of hash chains for which the length
for members of that chain is the same.
Dec onstat -b
of len The length of the chains. Dec
total chains The number of hash chains (buckets) created. Dec
hashed buffs The number of buffer headers hashed into the hash buckets. Dec
total buffs The number of buffers in the buffer pool. Dec
NOTES
• The onstat -h command does not show up in the normal onstat command usage.
TUNING & MONITORING
Tuning to the hash chain is performed indirectly by tuning the number of buffers. As pages are
read into the buffer pool, the page number is hashed to a value for one of the hash buckets. Since
there are only a limited number of hash buckets, multiple page numbers will hash to the same
value and thus the same hash bucket, creating a chain. Although the onstat -h command doesn’t
show the length of each individual hash bucket, it does show the total number of hash buckets
with a particular length.
buffer hash chain length histogram
# of chains of len
95 0
123 1
37 2
1 3
256 total chains
161 hashed buffs
200 total buffs
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