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The DBA and Database Performance Factors

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A database is an organized collection of data. The data are typically organized to model aspects of reality in a way that supports processes requiring this information. For example, modelling the availability of rooms in hotels in a way that supports finding a hotel with vacancies.

The DBA and Database Performance Factors

Response Time

“Response Time” is what users (and application servers!) see. They do not see ‘consistent gets’ or ‘redo size’ or ‘enq: TX – row lock contention”.

User perception of a system’s usability is significantly impacted by Response Time. “fit for use” (the application is usable) must co-exist with “fit for purpose” (the application does what it is supposed to do). On the other hand, Response Time for a batch job can vary from execution time for a (significant) single SQL call to the elapsed time for a key stage in the job.

Tiers

There are very many tiers through which a response reaches a user (or an application server, depending on who/what has “response issues”). From the desktop, via a browser, over the internet/intranet to an application server, rewritten as an SQL call to the database, parsed and executed by the database, CPU and I/O cycles consumed to fetch, filter and compute values, round-trips between the application server and database server, formatting on the application server, latency down to the user’s desktop; there are very many tiers that are comprised in an application’s performance. Such tiers also exist in a batch job – often ignored are the round-trips between the application server and database server.

Capacity

Each “component” (be it the User’s Desktop or the WAN Link or the App Server CPU or the App Server RAM etc … down through the Tiers) has a defined Capacity – theoretical and practical. Within a database instance, also, there are capacity parameters – e.g. SGA sizing parameters, the processes parameter etc.

Usage

Usage of the available capacity of any component varies from time to time. Any tool that “measures” usage has to collect a snapshot of usage at a certain point in time. Multiple snapshots must be analyzed together.

Throughput

Throughput is the volume of “load” (Transactions/Queries/Rows/Users – each is a different facet of “load”) that is being serviced by the “system”.

Constraints

Capacity is a constraint. Concurrency is a constraint as well. Two users/processes/sessions may not be permitted to modify the same row/resource at the same time.

Serialisation

Because Capacity is not Unlimited and because there are Constraints (automatic/system/artificial/user-defined), there may well be some points in application code or database code or the operating system where serialisation occurs.

Requirements

Volume requirements, usability requirements and control requirements are defined by users / analysts and must be built into the “system”. Requirements also add to code complexity.

Scalability

Scalability of the system is it’s ability to handle additional workload without more than a proportional increase in component resources (CPU, RAM, I/O) usage. Scalability is adversely impacted by points of contention or serialisation in the requirements / design / code.

Non-Linearity

Many systems are non-linear. If a query that processes ten thousand rows that are always in memory and never overflows to disk for Group/Sort operations takes 1second to run, it doesn’t necessarily follow that a hundred thousand rows would take 10seconds. The hundred thousand row query may require multiple disk reads because not all rows are cached in memory and, furthermore, the Group/Sort operations also overflow to disk.

Shared Resources

A database server may be configured to host multiple databases. The CPU and I/O load of one or more “other” databases may well be “interference” in the performance of a database under review. The “cost” of such “interference” must be computed and accounted for. Similarly, within a database, Batch reports may interfere with online queries. Also, when multiple schemas (e.g. for different “applications”) are provided for within a database, they share and contend for shared pool, library cache and buffer cache resources as well as for CPU and I/O.

These basic Factors apply to any System. They apply to Airports and Aeroplanes. They apply to Factories and Refineries. They apply to Hotels and Restaurants. They apply to Applications using Oracle Databases. As an Oracle Database Performance Analyst (a DBA or a Developer or a System Administrator), it is necessary to be aware of these Factor

Some database terms to know

Access organizes your information into tables: lists of rows and columns reminiscent of an accountant’s pad or a spreadsheet. In a simple database, you might have only one table. For most databases you will need more than one. For example, you might have a table that stores information about products, another table that stores information about orders, and another table with information about customers.

Each row is more correctly called a record, and each column, a field. A record is a meaningful and consistent way to combine information about something. A field is a single item of information — an item type that appears in every record. In the Products table, for instance, each row or record would hold information about one product. Each column or field holds some type of information about that product, such as its name or price.

The Importance of Database Design Reviews

Design reviews are an important facet of the system development lifecycle for database applications. It is during the design review that all aspects of the database and application code are reviewed for efficiency, effectiveness, and accuracy. It is imperative that all database applications, regardless of their size, are reviewed to assure that the application was design properly, efficient coding techniques were used, and the database is accessed and modified correctly and efficiently. The design review is an important process for checking the validity of design decisions and correcting errors before applications and databases are promoted to production status.

Multiple design reviews should be conducted over the course of an application’s life. There are seven basic design review phases for a database application:

A database is an organized collection of data. The data are typically organized to model aspects of reality in a way that supports processes requiring this information. For example, modelling the availability of rooms in hotels in a way that supports finding a hotel with vacancies.

The DBA and Database Performance Factors

Response Time

“Response Time” is what users (and application servers!) see. They do not see ‘consistent gets’ or ‘redo size’ or ‘enq: TX – row lock contention”.

User perception of a system’s usability is significantly impacted by Response Time. “fit for use” (the application is usable) must co-exist with “fit for purpose” (the application does what it is supposed to do). On the other hand, Response Time for a batch job can vary from execution time for a (significant) single SQL call to the elapsed time for a key stage in the job.

Tiers

There are very many tiers through which a response reaches a user (or an application server, depending on who/what has “response issues”). From the desktop, via a browser, over the internet/intranet to an application server, rewritten as an SQL call to the database, parsed and executed by the database, CPU and I/O cycles consumed to fetch, filter and compute values, round-trips between the application server and database server, formatting on the application server, latency down to the user’s desktop; there are very many tiers that are comprised in an application’s performance. Such tiers also exist in a batch job – often ignored are the round-trips between the application server and database server.

Capacity

Each “component” (be it the User’s Desktop or the WAN Link or the App Server CPU or the App Server RAM etc … down through the Tiers) has a defined Capacity – theoretical and practical. Within a database instance, also, there are capacity parameters – e.g. SGA sizing parameters, the processes parameter etc.

Usage

Usage of the available capacity of any component varies from time to time. Any tool that “measures” usage has to collect a snapshot of usage at a certain point in time. Multiple snapshots must be analyzed together.

Throughput

Throughput is the volume of “load” (Transactions/Queries/Rows/Users – each is a different facet of “load”) that is being serviced by the “system”.

Constraints

Capacity is a constraint. Concurrency is a constraint as well. Two users/processes/sessions may not be permitted to modify the same row/resource at the same time.

Serialisation

Because Capacity is not Unlimited and because there are Constraints (automatic/system/artificial/user-defined), there may well be some points in application code or database code or the operating system where serialisation occurs.

Requirements

Volume requirements, usability requirements and control requirements are defined by users / analysts and must be built into the “system”. Requirements also add to code complexity.

Scalability

Scalability of the system is it’s ability to handle additional workload without more than a proportional increase in component resources (CPU, RAM, I/O) usage. Scalability is adversely impacted by points of contention or serialisation in the requirements / design / code.

Non-Linearity

Many systems are non-linear. If a query that processes ten thousand rows that are always in memory and never overflows to disk for Group/Sort operations takes 1second to run, it doesn’t necessarily follow that a hundred thousand rows would take 10seconds. The hundred thousand row query may require multiple disk reads because not all rows are cached in memory and, furthermore, the Group/Sort operations also overflow to disk.

Shared Resources

A database server may be configured to host multiple databases. The CPU and I/O load of one or more “other” databases may well be “interference” in the performance of a database under review. The “cost” of such “interference” must be computed and accounted for. Similarly, within a database, Batch reports may interfere with online queries. Also, when multiple schemas (e.g. for different “applications”) are provided for within a database, they share and contend for shared pool, library cache and buffer cache resources as well as for CPU and I/O.

These basic Factors apply to any System. They apply to Airports and Aeroplanes. They apply to Factories and Refineries. They apply to Hotels and Restaurants. They apply to Applications using Oracle Databases. As an Oracle Database Performance Analyst (a DBA or a Developer or a System Administrator), it is necessary to be aware of these Factor

Some database terms to know

Access organizes your information into tables: lists of rows and columns reminiscent of an accountant’s pad or a spreadsheet. In a simple database, you might have only one table. For most databases you will need more than one. For example, you might have a table that stores information about products, another table that stores information about orders, and another table with information about customers.

Each row is more correctly called a record, and each column, a field. A record is a meaningful and consistent way to combine information about something. A field is a single item of information — an item type that appears in every record. In the Products table, for instance, each row or record would hold information about one product. Each column or field holds some type of information about that product, such as its name or price.

The Importance of Database Design Reviews

Design reviews are an important facet of the system development lifecycle for database applications. It is during the design review that all aspects of the database and application code are reviewed for efficiency, effectiveness, and accuracy. It is imperative that all database applications, regardless of their size, are reviewed to assure that the application was design properly, efficient coding techniques were used, and the database is accessed and modified correctly and efficiently. The design review is an important process for checking the validity of design decisions and correcting errors before applications and databases are promoted to production status.

Multiple design reviews should be conducted over the course of an application’s life. There are seven basic design review phases for a database application:

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