Interview Questions.

Q1. What Is The Size Of Informix Page?

The maximum not unusual web page length used is 2KB, though a few systems makes use of 4KB page.

Q2. What Is Extent In Informix?

If a desk is designed without specifying quantity sizes, Informix makes use of a default of 16 pages for the primary and 8 pages for each subsequent quantity. Extent sizing is done when the desk is first of all created.

Q3. What Are The Informix Isolation Levels And Can You Explain Each One ?

DIRTY READ: Reads the records with out checking if it’s committed or now not. No locks are held throughout the read

COMMITTED READ: Reads best the dedicated information. No locks held

REPEATABLE READ: Reads handiest the committed records. A shared lock is held on the rows. Other sessions can achieve shared locks on the ones rows, but nobody can get an different lock.

CURSOR STABILITY

Q4. What Command Would You Use To Move The Physical Log?

Onparams -p -s -d -y

onmonitor software

in more moderen IDS variations, use the SQL API to adjust the plog location

Q5. I Think I Screwed Up My Onconfig File, And I Do Not Have A Backup Of It. What Should I Do?

If Informix continues to be on-line, you may get a new onconfig with:

onstat -c >onconfig

If Informix is offline, you can retrieve the settings from the database with:

oncheck -pR

or

oncheck -pP 1 1

Q6. What Are The Sql Joins Available In Informix?

INNER JOIN, LEFT / RIGHT OUTER JOIN, FULL OUTER JOIN, CROSS JOIN

Q7. Explain The Purpose Of Optimizer Directives And How/why You Would Use Them

A DBA can use directives in the main to trade / test / compare the execution plan (charges / blessings) for a question, through forcing an index / trade be part of order / and so forth.

Q8. Mention The Database Server Operating Modes Available For Informix?

Informix IDS offer following modes:-

Online mode: This is the regular running mode of the database server.

Offline mode?: The database server isn't always walking. Shared reminiscence is not allotted.

Quiescent mode: This is the regular working mode of the database server.

Administrators use this mode to carry out renovation capabilities that do not require the execution of SQL and DDL statements. Only the administrator (consumer informix) can access the database server.

Single-User mode: This mode is an middleman mode between Quiescent mode and Online mode?

Administrators use this mode to perform any preservation task, consisting of tasks requiring the execution of SQL and DDL statements. Administrators can also perform all other features to be had in Online mode. You can see the contemporary database server mode with the aid of executing the onstat - application from the command.

Q9. What Is Informix Universal Server?

Informix Universal Server changed into the logo call given to the 9.X variations of the product; the upgrade from the Informix Dynamic Server (IDS) 7.X merchandise, skipping the XPS 8.X launch numbers. The nine.X server contained some of functional advances (data kind extensibility, DataBlades and so forth), in addition to upgrades to the storage manager and SQL processing. The most current versions of the Informix line -- 10.X -- are an evolutionary progression over the 9.X engine.

Q10. How Would You Check That A Given Index Is Consistent And Has No Corruption? If Corruption Occurred On A Database What Would Your Process Be?

Index (together with database and table) consistency can be tested with oncheck -cDI database_name:table_name. Preferably with the instance put in quiescent mode.

If just the index is corrupted (and not fixable by using oncheck), an alternative might be to recreate the index.

Q11. What Can Be Used To Capture An Isam Error From An Informix Odbc Program On Unix ?

If the DBA has a query interior a script / software that connects to an Informix example via an ODBC connection, and going for walks the query outcomes in an blunders, then he can use the TRACE capability, and go back DBINFO(sqlca.Sqlerrd[1,2]).

Q12. What Is The Option Or Command Used In Informix For Finding Which Dbspace A Database Resides?

From command line# onmonitor ->Logical-Logs->Databases.

Q13. What Are The Uses Of Key Value Locking In Informix?

The database server uses a idea referred to as key-price locking to fasten the deleted row. When the database server deletes a row, key values in the indexes for the table aren't eliminated straight away. Instead, every key fee is marked as deleted, and a lock is located on the key cost. One of the most vital makes use of for key-value locking is to guarantee that a unique key stays unique thru the give up of the traction that deleted it.

Q14. What Are The Options/commands Used Which Dbspace A Database Resides?

The DBA can use:

The onmonitor software greater

A question becoming a member of sysdbspaces and sysdatabases tables positioned within the sysmaster database

Q15. Why Is Update Statistics Important To A Database?

Running update records will update the machine catalog statistics approximately the database.

This facts is utilized by the Informix optimizer to calculate costs and execution pl for day after day queries. Lack of up to date facts about statistics distributions may also bring about seriously horrific pl.

Q16. Can I Ask About Perl, Dbi And Dbd Informix? Other Products?

You may ask questions on Perl, DBI and DBD::Informix, however handiest if an IBM or Informix database is concerned, by some means -- it isn't a trendy forum for arbitrary questions about Perl. However, there are alternative boards which you must additionally use, defined inside the product. 

Q17. What Is The Informix-listing

The informix-listing@iiug.Org mailing listing is a bi-directional gateway to the comp.Databases.Informix (c.D.I) UseNet news institution. Messages posted to the news group are forwarded by means of mail to subscribers of the mailing listing; responses despatched to the informix-list@iiug.Org e mail address also are posted to the information organization; and the gateway manages to preserve tune of factors so that postings do no longer repeat themselves. The mailing listing is 'closed' in which you cannot publish immediately to the list unless you also enroll in the listing. However, you may constantly submit to the news group as a substitute; this is fully open and unmoderated.

Q18. Can You Explain Pdq Priority?

By putting PDQ PRIORITY the DBA can exchange the question execution priority and growth the variety of internal threads spawned by way of Informix to satisfy the question. Also, a few memory allocation techniques fluctuate upon placing PDQPRIORITY.

Q19. Explain The Concept Of Fragment Elimination In Informix ?

Fragment removal seems whilst the following situations are all happy:

A table is fragmented

The fragmentation components doesn’t create overlapping ? Asta oricum nu e permis (overlapping)

A question uses equality filter on a column used in the fragmentation formulation

If the above conditions are met, the Informix engine can pass fragments (statistics is not searched there) that don’t follow the question filter
 

Q20. Who Developed Informix?

IBM launched Informix

Q21. What Is An Extent In Informix?

In Informix, the smallest unit containing records is the “page”. A non-stop group of pages shape an extent

Q22. What Is An Informix Instance?

A series of informix processes in fee of:

Informix shared memory structures

Receive person session connection, and places them in touch with the records

Gather facts records

Allow backup / healing moves

Interact with the person periods

At the OS level, an example may be “visible” as one ore greater oninit techniques + reminiscence systems + disk / persistence structures

Q23. What Is Informix Instance?

An Informix instance is a single connection to shared reminiscence. It is represented by way of one or greater on init methods. When Informix is started out or stopped, those processes appear and disappear. Informix used to apply the time period "server" whilst regarding an example, therefore the surroundings variable DBSERVERNAME.

Q24. What Can Be Used To Capture An Isam Error From An Informix Odbc Program On Unix?

We can use the SQLCA structure to get the ISAM Error.

Sqlca.Sqlerrd[1] holds the ISAM error return code.

We can also use the rgetlmsg() and rgetmsg() library capabilities to acquire ISAM mistakes message textual content.

Q25. Somehow Informix Fails To Go Online. Is There A Way To View What Oninit Is Doing?

Yes, you can start Informix in verbose mode:

oninit -v (this works on NT as well)

Informix will print the whole thing that happens.

To close the verbose mode: start a 2d terminal consultation (UNIX) or command activate (NT) and execute:

onmode -ky

N.B. Don't close your terminal consultation (UNIX) or command activate (NT) even as in verbose mode. This will take Informix offline right now.

Q26. What Is Chunk In Informix?

A chew is a bodily portion of disk on which Informix stores its facts. A chew can be both a uncooked partition or a file machine report. Informix indicates that a bit's call be a symbolic hyperlink to the actual chunk. For example, in case you are the usage of /dev/rdsk/c6t0d0s1 as a piece, you can create a symbolic hyperlink named /dev/informix/chunk1 that factors to /dev/rdsk/c6t0d0s@That manner, if there are ever any troubles with that disk, you may update the disk with any other one and just alternate the symbolic hyperlink.

Q27. What Are The Database Server Operating Modes Available For Informix? Explain Each.

ONLINE : example is up & walking, permitting connections from all the customers (which have the essential grants)

OFFLINE: instance is down. No connections to the database allowed

SINGLE USER: example is up & going for walks, however simplest user informix can get entry to the database. Useful while DBA wants to close all of the person periods, carry out a few task and convey the example in multi person mode

QUIESCENT: Similar with SINGLE USER mode, beneficial for renovation project (healing / recovery of a corrupt or offline dbspace bite)
 

Q28. Explain About Light Sc In Informix?

Light sc arise under the following situations: The optimizer chooses a sequential scan of the desk. The variety of pages inside the table is more than the quantity of buffers inside the buffer pool. The isolation stage obtains no lock or a shared lock on the desk: Dirty Read (consisting of non logging databases) isolation level Repeatable Read isolation degree if the table has a shared or special lock Committed Read isolation if the desk has a shared lock

Q29. Why A Foreground Write In Informix Decrease Performance?Country The Reason For The Same?

Foreground writes (FG) need to usually be zero. A foreground write is brought on whilst a consultation desires to have a web page from disk located into the buffer pool, but there are no clean/loose buffers to be had. In this case, the sqlexec thread will pick out a page off the least currently used side of an LRU queue, write it out, and mark the web page as clean. This technique is time ingesting for a session and have to be avoided.

Q30. Explain About Light Sc In Informix ?

A mild test can also occur whilst Informix internal optimizer comes to a decision that the best execution plan may be a sequential scan (horrific question selectivity, loss of indexes…). In this example, if the optimizer similarly makes a decision that the records set due to the question will not match inside the buffer pool, it will skip it. The end result is a light test.

Q31. What Is A Chunk In Informix ?

The “chunk” is a record containing informix database information (or a subset of that data). In can be a report on a inner disk (cooked document) or a raw device (from a SAN platform or inner disks/arrays).

Q32. How Could You Increase The Speed Of Ontape/onbar Backups ?

On a platform with rapid cpus, write low overall performance and compresable facts, the ontape output may be piped and compressed earlier than getting on disk (less IO write operations).

With onbar, greater backup speeds can be achived by means of:

Increase the number of onbar threads -> BAR_MAX_BACKUP

Increase the buffers used by onbar (if reminiscence is to be had) ? BAR_NB_XPORT_COUNT

Use a fast storage for the garage pool (We use onbar + IBM Tivolli Storage Manager)

Consider taking incremental backups

Q33. Explain Checkpoints And Why In 9.Four They Were Better Than In Previous Versions Of The Engine?

You are still the use of nine.Four ? It’s out of assist for 3 years … . We upgraded from 10.00FC6 to eleven.50FC7 closing year.

The first Informix database I began to administrate became IDS 10.00FC@So my great wager is that 9.Four added partially non blockading checkpoints (fuzzy checkpoints ?), these being superseded in the latter variations.

The checkpoint is the moment when Informix will flush the contents from the bufferpool to disks.

Q34. Why Do Foreground Writes Decrease Performance ?

Whenever Informix sqlexec procedure searches for a loose / clean buffer a good way to study a web page from the disk into that buffer is referred to as foreground write operation. The performance penalty seems while there are no loose / clean buffers left, and sqlexec has to look for a less used buffer, write its content to disk, smooth the buffer and reuse the buffer for a foreground write operation – having the disadvantage of NOT being asynchronous (as chew writes/lru writes)

Q35. What Rules Exist Regarding Format, Content, Flame Wars, Etc

None; that is a news institution! That is, there are not any guidelines enforced by way of the software. There are periodically discussions on c.D.I approximately what ought to and must not be stated. This is my FAQ, so it receives my spin on the policies that should be observed.

* Format: HTML postings are strongly discouraged; so are MIME postings. Both cause issues with many often used information readers. That me that attachments aren't encouraged either. Also, sending the same facts twice, as soon as in HTML and as soon as in undeniable textual content, is downright wasteful.

Q36. An Index Is Reaching A Limitation On The Number Of Pages It Has, Can You Explain Why This Limitation Exists And What Work You Would Do To Get Around It?

A dbspace may have one or greater partitions. Each partition has a special “header” data in the first quantity.

The partition header keeps a list of the partition’s extents. If the item holding the space inside the partition (desk / index) has a extremely good variety of extents, the header might not be able to maintain the whole listing.

Workarounds:

growth first / next quantity size and recreate the item

exchange the web page length -> will bring about a lower quantity of extents

recreate the index in a dbspace having a larger web page size

Q37. Can I Install Informix On A Non-english Version Of Windows Nt?

Yes, but you need to install version 7.30 TC 6 or higher.

Q38. What Is A Binary Large Object ?

Any object for whom its binary information document may be stored and restored with fulfillment into a database may be considered a BLOB.

As an example, an ecommerce web site can shop the product snap shots and motion pictures inner a database. But that’s now not a pleasant practice.
 

Q39. What Is Informix Binary Large Object?

A binary large object, additionally referred to as a blob, is a collection of binary facts stored as a single entity in a database management machine. Informix invented an alternative backronym, Binary Large Object. Blobs are generally pics, audio or other multimedia gadgets, though every now and then binary executable code is stored as a blob.

Q40. And Why Are These Important ?

Monitor effect on device’s CPU:

Instance sys vcpu + Instance consumer vcpu

Locks requests / waits

Active locks

Monitor effect on system’s storage (IO) / reminiscence:

Buffer reads / writes / waits

Page reads / writes /

Disk reads / writes

Logical competition:

lock requests / waits

deadlocks

eventually rollbacks

Monitor example health & fame

Dbspaces total / used / free space

Checkpoint intervals & period

Sequential sc wide variety

Number of no longer yet backup-ed logical logs

Number of active classes

And of route the example on line log.
 

Q41. Who Conceived And Designed The Informix Database Management System?

The Informix database management gadget turned into conceived and designed through Roger Sippl within the overdue 1970s. Informix turned into based in 1980, went public in 1986, and for a length at some point of the Nineteen Nineties Informix turned into the second most famous database machine, after Oracle.

Q42. How Would You Convert A Secondary Server Into A Primary Server ?

EXECUTE FUNCTION project(“ha sds number one”,”srv_slave”);

If it's far HDR and the secondary becomes the brand new standalone server: onmode -d wellknown