Process Control Block

Process Control Block (PCB, also called Task Controlling Block, Task Struct, or Switchframe) is a data structure in the operating system kernel containing the information needed to manage a particular process.

Process state. The state may be new, ready, running, waiting, halted, and so on.

Program counter. The counter indicates the address of the next instruction to be executed for this process.

CPU registers. They include accumulators, index registers, stack pointers, and general-purpose registers, plus any condition-code information. Along with the program counter, this state information must be saved when an interrupt occurs, to allow the process to be continued correctly afterward.

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There is audit trial requirement that need to be captured into log table these day. But we suffer from the limited function provided by Sybase ASE DB in order to achieve our goals. SybaseASE 12.5 does not support neither analytic function nor row number column, and therefore we have to implement cross comparison by ourselves via basic semantics.

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--create rownum column
select rownum = identity(10), * from #temp_table from table where 1=2
insert into #temp_table
select * from table where pid = @pid
insert into #temp_table
select * from table_history where pid = @pid order by audit_update_date desc
--use self-join to match the cross rows
select a.rownum,
		case when a.col1 = b.col1 then 'equal' else 'inequal' end
from #temp_table a left out join #temp_table b on ( a.pid = b.pid and (a.rownum + 1) = b.rownum )
where ...

In contrast, we also provide oracle version of implementation.

In practice, we will meet the requirement to rotate the table including convert cols to rows, convert rows to cols. In this session, I'll produce the solution in common method as well as db-specified features.

Convert columns to rows

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--common solution
select * from (
	select id, 'col_1' as col_name, col_1 as col_val
	from table
	union all
	select id, 'col_2' as col_name, col_2 as col_val
	from table
	union all
	... 
) order by id

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--oracle 11g unpivot query
select *
from table
unpivot (
	col_val for col_name in (col_1 as 'col_1', col_2 as 'col_2')
)
order by id

Concert rows to columns

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--common solution
select id,
	max(case when col_name = 'col_1' then col_val else null end) as col_1,
	max(case when col_name = 'col_2' then col_val else null end) as col_2,
	...
from table
order by id

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--oracle 11g pivot query
select *
from table
pivot (
	max(col_val) for col_name in ('col_1' as col_1,'col_2' as col_2)
)
where ...
order by id

Excel pivot table

For non-sql approaches, we can use excel pivot table. Excel spreadsheets are a great way to pivot and analyze Oracle data, and tools.

The aim of this post is to review the crucial terms of operating-system and basic interaction of these underlying components.

Before starting with topic, I am going to reveal why I try to read books of OS related at this point. Let me conclude the reasons, first and foremost, various applications in my daily work encounter issues that are associated with LINUX system, such as buffer size, open file limits and unable to create native threads etc. All of these issues point out to the knowledge of OS. Next, Java performance tuning is always based on the operating system concept, like memory management, cpu utilization etc. Furthermore, including all the design concepts are derived from the solution of common issue inside operating system.

Due to these, it is so encouraged to read and go through operating system concept again that I could be inspired and get everything tied. If there are any findings or association with Java, I will make more explanations and comments linked with definitive resource.

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