computer science

Quiesce

Quiesce is a computer science topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand Quiesce rather than just read about it. In short: To quiesce is to pause or alter a device or application to achieve a consistent state, usually in preparation for a backup or other maintenance. Description In software applications that modify information stored on disk, this generally involves flushing any outstanding writes; see buffering.

Key takeaways

Quiesce belongs to computer science; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect Quiesce to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Quiesce from memory before moving on to harder problems.

Reference excerpt

To quiesce is to pause or alter a device or application to achieve a consistent state, usually in preparation for a backup or other maintenance.

Description In software applications that modify information stored on disk, this generally involves flushing any outstanding writes; see buffering. With telecom applications, this generally involves allowing existing callers to finish their call but preventing new calls from initiating.

Example Perhaps the best known support for this was incorporated into Microsoft Shadow Copies which was introduced in Microsoft Windows Server 2003. For an application to be quiesced during the shadow copy process, it must register itself as a writer and it is responsible for putting itself into a quiescent mode upon notification.

Vendor schemes Various database and application vendors implement schemes to provide support for this feature including:

Symantec's Livestate – now includes a quiesce process, as does VMware's VI3 snapshot and VCB features. Symantec supports Exchange and SQL. VMware support – IO system IBM DB2 LUW supports a Quiesce command that is used to indicate a state for which all users have been locked out of a database or an instance (of databases) so that administrative tasks can be performed. IBM DB2 for z/OS, OS/390 and IBM i Operating System has a utility command called QUIESCE, used in order to make it write all data belonging to a certain database (a logical entity in a DB2 subsystem) from the buffers, helping utility programs get DRAIN access on the datasets quickly. IBM DB2 for z/OS and OS/390 also supports a command SET LOG SUSPEND that technically speaking, stops it from writing to the log, in fact freezing any database activity (except for most queries). This mode is used sometimes for snapshot type backup schemes, thus only lasting for less than a second, ensuring backed up data is in a consistent state. This command is reversed with a SET LOG RESUME command. A graceful shutdown of WebSphere MQ is called quiescing. ORACLE also supports a Quiesce command since version 9i which allows existing users to continue to use resources but disallows new resources being made available. SYBASE ASE 12.0 and above support a QUIESCE DATABASE command that prevents any process from running commands that write to the transaction log. The primary purpose is to stop all update activity so the database files can be copied or backed up using OS level utilities. While the database is quiesced, it is still available to users for read-only queries. Microsoft Windows SharePoint Services 3.0 and Microsoft Office SharePoint Server 2007/2010 support a QUIESCE or QUIESCE FROM TEMPLATE (2010) option within the Central Administration operations window. This allows an administrator to stop the server farm from accepting new user connections and gradually brings any long-running applications offline without causing data loss. JADE Object Oriented Database system can perform a quiesced backup with the parameter 'quiesced=true'. The database is placed in a quiescent state by allowing current active transactions to complete and then flushing modified buffers from cache to the stable database. During a quiesced backup, updating transactions are not permitted and attempts to execute database transactions raise a database exception. Microsoft Visual Studio Team Foundation Server supports quiesce functionality by using the TFS Service Control command-line utility. More information exists about this command-line utility in the MSDN Library. A Microsoft Knowledge Base article describes it by indicating that it disables access to Team Foundation Server services for the duration of servicing operations.

See also The dictionary definition of quiesce at Wiktionary

References

Worked examples

Example 1 — a first encounter with Quiesce

Start with the simplest possible case. Write down what Quiesce claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In computer science, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to Quiesce before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about Quiesce ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of Quiesce

In research: Quiesce appears in computer science research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses Quiesce in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: Quiesce is common in secondary-school and first-year university syllabi. It links to neighbouring topics Computer hardware tuning, Computing terminology, so understanding it makes those chapters shorter.
In everyday life: Look for Quiesce outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

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How to study Quiesce in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Quiesce means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain Quiesce out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Quiesce in simple terms?

To quiesce is to pause or alter a device or application to achieve a consistent state, usually in preparation for a backup or other maintenance. Description In software applications that modify information stored on disk, this generally involves flushing any outstanding writes; see buffering.

Why does Quiesce matter?

Because it connects several computer science ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study Quiesce?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on Quiesce.