Week 4 L1

Question 1

How to insert a document ?

Answer 1

.insert

Question 2

How to insert datasets such as JSON CSV and TSV?

Answer 2

use mongo import

Question 3

how to specify format of import?

Answer 3

/type

Question 4

What happens if no collection name is given ?

Answer 4

the collection is named from file without extension

Question 5

How do you remove any blanks from insert?

Answer 5

/ignoreBlanks

Question 6

what does upserting data mean ?

Answer 6

/mode upsert

Upsert inserts new data but replaces any matching data. Inserts if no match or updates if it does.

Question 7

How to specify fields for upsert?

Answer 7

/upsertFields

Question 8

How to specify field names?

Answer 8

/fields name

Question 9

How to specify list of field names

Answer 9

/headerline

Question 10

How to export data?

Answer 10

mongoexport

Question 11

How to export part of a collection

Answer 11

/query

Question 12

How to export a subset of names of fields

Answer 12

/fields title

Question 13

how to sort a export ?

Answer 13

/sort

Question 14

how to reduce number of exported documentes

Answer 14

/skip and /limit

Question 15

What are indexes

Answer 15

Special data structures that store small portions of collections data set in a easy to traverse form. Indexes store values of specific fields or set of fields ordered by value of field. Each entry in index points to DB document.

Question 16

Why do we use indexes?

Answer 16

To support efficient execution of queries in mongo db.
Without indexes Mongodb must scan every document in a collection to select those documents that match the query criteria.

Question 17

At what level does mongodb define its indexes?

Answer 17

At collection level

Question 18

What structure do indexes in mongo db use?

Answer 18

B-Trees

Question 19

What is the big O notation of a non index look up ?

Answer 19

O(N)

Question 20

What is the big O notation when using a B tree ?

Answer 20

O(log n)

Question 21

Benefits of index

Answer 21

Held In ram
Results are also already sorted so no need for additional sort after query
Covered results do not need to access DB at all, just return data from the index.
Range searches are quicker

Question 22

How do we measure the efficiency of a search ?

Answer 22

Using the explain method

Question 23

What are the different types of index in mongodb?

Answer 23

Default ID index
Single field index , compound index,
multikey index- index array fields,
geospatial index, 
text indexes,
hashed indexes

Question 24

What are some examples of mongodb index properties?

Answer 24

unique indexes- reject duplicate values from index fields.

sparse indexes- only index docs that have a index fields, so only contains subset of whole collection

Question 25

why should you be careful with the amount of indexes you use?

Answer 25

should only index what oyu need as too many indexes can fill ram.
Index should be for frequent and targeted queries and updates.
Indexes will slow down large number of insert updates and deletes as the index will also need to be changed.

Question 26

What is index hinting ?

Answer 26

If you search across many fields and there are more than one field with index and there’s no compound index then hint tells mongo db optimises which index to use