The update takes a long time

Hi we have a customer_status of the table where we have the following columns such as contacted_date and status

Under certain conditions, it will read all lines and update the data

as the customer_status UPDATE

SET contacted_date = < some_date >

When status = 0 and contacted_date is set to null

It's taking a long time and have hanged...

Please let me know what I need to check in what concerns the DB from Redolog setting or any other setting that I am basically a developer all

The current version of the DB is:

Oracle Database 11 g Enterprise Edition Release 11.2.0.4.0 - 64 bit Production

CUSTOMER_STATUS

CONTACTED_DATE TIMESTAMP

STATUS NVARCHAR (1)

Any suggestions would be much appreciated.

I've seen this kind of problem before and there is no simple answer.  You are better off watching a redesign, otherwise, you will have to resort to brute force tactics to improve performance.  And even then the best you can do is still very limited.

If you have a table "customer_status" with a "status" column that has probably only 2-0 and 1 values.  This means that the optimizer will believe, in the absence of all histograms for each value to roughly half of the rows in the corresponding table.  Think about it, it makes sense.  In turn, that means that the optimizer is more likely to choose a full table scan to run the UPDATE.  In turn, which means that as time passes and the table grows then the update becomes slower and slower every time that it is executed.

Solution?  A redesign.  Really, it's the "best solution".  Otherwise you still go to the fight against the problem that the "Status" column has only 2 values in it and Oracle can assume that half of the lines end with each value.  With these statistics, the optimizer will always choose a full as table scan being the cost lowest and as the table grows so the update is slower.

You can try to create an index on the status and contacted_date on customer_status (status, contacted_date).  But that works only if the "status" has a NOT NULL constraint on it, which does not appear in your column definitions.  Without that the index would be always useless and Oracle would still do a full table scan.

You would also go the questions that your query uses a 0, which is a NUMBER, but the definition of the column is of type NVARCHAR and Oracle will add an implicit conversion around the column to convert number in the execution of the query, which again once stops using the index on two columns.  Data types must match for an index to use.

You could create a histogram of frequencies located on the 'Status' column so that the optimizer has more precise statistics.  But this can depend on when in the day, the table statistics are collected.

These tables tend to be very dynamic with data changing in their breast. How many lines in this table?  Are all deleted?  Or they stay there forever?  How many times does change the status value?  Or it fixed once and stay the same forever?

I've seen problems of treatment of systems with a table of 'work' with a "status" column on work, and depending on what time of the day, statistics were collected from this table, it could have vastly different numbers of lines in there and a different number of lines with different values for the 'status '.  Ultimately we did an overhaul and separate tables used - one for in the expectation of work - and one for completed tasks that kept the data sets smaller and meant that the table 'pending' only pending works in.

John

Tags: Database

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