Data Management Systems at ETHZ - ETH Zurich | Flashcards & Summaries

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Lernmaterialien für Data Management Systems an der ETHZ - ETH Zurich

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TESTE DEIN WISSEN

Hybrid-histogram improves accuracy for “almost popular” values.

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True

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Looping Sequential (LS) pattern

If the table is too large to fit into memory (i.e., the locality set size cannot be achieved), most suitable prefetching strategy?


Prefetch next page(s)

No suitable prefetching strategy

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TESTE DEIN WISSEN

Prefetch next page(s)


Prefetch the next pages in the relation as the looping is sequential (with back-tracking). Note that if the locality set size is met, there is no need to prefetch as everything is already in-memory anyways.

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Select the advantages of the thread per worker approach

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Shared data is easily accessed

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What are update locks?

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Locks for updates but they do not allow to write

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Assume a table T with an attribute "salary" and a B+-tree index built over that attribute. Can the query be answered by just looking at the index and without having to retrieve any data from the base table?

SELECT salary, COUNT(*)
FROM T
Where salary < 20000
GROUP BY (salary)


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Yes -- Start from the beginning of the index (at the leaves). For every distinct value of salary encountered, count how many entries have the same salary and add to the result. Stop when the salary value >= 20000.


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What data do blocks contain when storing a table?

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Header says what data is inside, when it has last been updated and other general info.

Table directory says what is the schema of the data that is stored on that block.

Row directory contains the actual data which are pointers to the actual tuples (rows) which are in the table (in this block).

Each tuple gets a block and a slot (where to put the tuple) in that block.

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What is a OS page?

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A page, memory page, or virtual page is a fixed-length contiguous block of virtual memory, described by a single entry in the page table. It is the smallest unit of data for memory management in a virtual memory operating system.

So it is the minimal size of transfer between main memory and disk.

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How is query optimization done?

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Relational algebra can prove the equivalence of certain transformations. An sql statement is transformed into an operator tree which can then be optimized based on those equivalences and knowledge or additional information, heuristics, cost estimation, etc.

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Why are free lists for each segment and not for each extent?

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Because a segment can have many extents and we don't want to traverse them to find a free list that has space.

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How does the database figure out where there is free space?

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A segment contains one or more free lists which contains pointers to blocks that have usable free space. Multiple lists is for parallel inserts or updates. These lists are updated as transactions execute with the PCTFREE (percentage free) and PCTUSED (percentage used) rules.

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What happens if the extent doesn't have enough space?

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Then we need to allocate another extent and put the block there. 

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Choose all the options that are byte addressable (random access) and not block addressable (sequential access)

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CPU Registers

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Q:

Hybrid-histogram improves accuracy for “almost popular” values.

A:

True

Q:

Looping Sequential (LS) pattern

If the table is too large to fit into memory (i.e., the locality set size cannot be achieved), most suitable prefetching strategy?


Prefetch next page(s)

No suitable prefetching strategy

A:

Prefetch next page(s)


Prefetch the next pages in the relation as the looping is sequential (with back-tracking). Note that if the locality set size is met, there is no need to prefetch as everything is already in-memory anyways.

Q:

Select the advantages of the thread per worker approach

A:

Shared data is easily accessed

Q:

What are update locks?

A:

Locks for updates but they do not allow to write

Q:

Assume a table T with an attribute "salary" and a B+-tree index built over that attribute. Can the query be answered by just looking at the index and without having to retrieve any data from the base table?

SELECT salary, COUNT(*)
FROM T
Where salary < 20000
GROUP BY (salary)


A:

Yes -- Start from the beginning of the index (at the leaves). For every distinct value of salary encountered, count how many entries have the same salary and add to the result. Stop when the salary value >= 20000.


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Q:

What data do blocks contain when storing a table?

A:

Header says what data is inside, when it has last been updated and other general info.

Table directory says what is the schema of the data that is stored on that block.

Row directory contains the actual data which are pointers to the actual tuples (rows) which are in the table (in this block).

Each tuple gets a block and a slot (where to put the tuple) in that block.

Q:

What is a OS page?

A:

A page, memory page, or virtual page is a fixed-length contiguous block of virtual memory, described by a single entry in the page table. It is the smallest unit of data for memory management in a virtual memory operating system.

So it is the minimal size of transfer between main memory and disk.

Q:

How is query optimization done?

A:

Relational algebra can prove the equivalence of certain transformations. An sql statement is transformed into an operator tree which can then be optimized based on those equivalences and knowledge or additional information, heuristics, cost estimation, etc.

Q:

Why are free lists for each segment and not for each extent?

A:

Because a segment can have many extents and we don't want to traverse them to find a free list that has space.

Q:

How does the database figure out where there is free space?

A:

A segment contains one or more free lists which contains pointers to blocks that have usable free space. Multiple lists is for parallel inserts or updates. These lists are updated as transactions execute with the PCTFREE (percentage free) and PCTUSED (percentage used) rules.

Q:

What happens if the extent doesn't have enough space?

A:

Then we need to allocate another extent and put the block there. 

Q:

Choose all the options that are byte addressable (random access) and not block addressable (sequential access)

A:

CPU Registers

Data Management Systems

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