Oracle Apps DBA: Keeping E-Business Suite Alive · Module 17 · When it is not the database
When it is storage
Lesson 174 of 184 · 3 min
Latency that LOOKS LIKE A DATABASE PROBLEM from every angle except THE ONE THAT MEASURES IT. Storage is the hardest of these to identify, because every database-level measurement points at the database. THE DATABASE REPORTS SESSIONS WAITING ON I/O, WHICH IS MODULE 11 LESSON 3'S SECOND CATEGORY. Everything looks like a database that is reading too much — and the ordinary response is to tune the SQL so it reads less, which is usually right. WHAT DISTINGUISHES A STORAGE PROBLEM IS THAT THE AMOUNT OF READING HAS NOT CHANGED AND THE TIME PER READ HAS. The same query reading the same blocks takes three times longer than last month. That is not a plan problem and no amount of tuning addresses it — the database is being answered more slowly by the thing underneath it. SO THE MEASUREMENT THAT SETTLES IT IS AVERAGE TIME PER READ, COMPARED AGAINST THE BASELINE.…
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