class RelCacheTable

The class RelCacheTable is used to cache Relation Catalog entries of all the open relations in NITCbase. The first two entries of the Relation Cache Table corresponding to RELCAT_RELID and ATTRCAT_RELID are reserved for storing the entries of Relation Catalog relation and Attribute Catalog relation, respectively. These are loaded into the cache by the OpenRelTable constructor at the start of the session. These relations remain in the cache memory throughout the session and can only be closed by the OpenRelTable destructor during shutdown.

The class contains a private member field, relCache, which is an array of pointers to struct RelCacheEntry with size MAX_OPEN. For each relation opened, an entry is made in the array relCache, at the index corresponding to the relation id of the relation. This entry points to the struct RelCacheEntry that stores all the attribute values of the relation's entry from the Relation Catalog block along with other meta-data of the relation.

The class provides public methods - getRelCatEntry() and setRelCatEntry() to retrieve and update the Relation Catalog Entry of a relation in the Relation Cache Table. The class also provides public methods getSearchIndex() and setSearchIndex() for retrieving and updating the searchIndex field of Relation Cache Entry.

The private method recordToRelCatEntry() is used to convert a record (implemented as an array of union Attribute) to RelCatEntry structure. This function is called by the friend class, OpenRelTable, while opening a relation. Similarly, the private method relCatEntryToRecord() is used to convert RelCatEntry structure to a record. This function is also called from the friend class, OpenRelTable, while closing a relation.

C++ Static Classes

RelCacheTable is a static class, that is, all member fields and methods are declared static. Memory is allocated statically for all member fields of the class. This static methods in this class is used to access its static member fields. C++ allows static methods to be accessed using the semantics class_name :: function_name().

note

The class OpenRelTable is a friend class to the RelCacheTable class. This allows all methods in OpenRelTable to access the private fields and methods of the RelCacheTable class.

The class definition of RelCacheTable is given below.

class RelCacheTable {

friend class OpenRelTable;

public:
  //methods
  static int getRelCatEntry(int relId, RelCatEntry *relCatBuf);
  static int setRelCatEntry(int relId, RelCatEntry *relCatBuf);
  static int getSearchIndex(int relId, RecId *searchIndex);
  static int setSearchIndex(int relId, RecId *searchIndex);
  static int resetSearchIndex(int relId);

private:
  //field
  static RelCacheEntry* relCache[MAX_OPEN];

  //methods
  static void recordToRelCatEntry(union Attribute record[RELCAT_NO_ATTRS], RelCatEntry *relCatEntry);
  static void relCatEntryToRecord(RelCatEntry *relCatEntry, union Attribute record[RELCAT_NO_ATTRS]);

};

The following are the specifications for the methods in class RelCacheTable.

RelCacheTable :: getRelCatEntry

Description

Gives the Relation Catalog entry corresponding to the specified relation from Relation Cache Table.

note

The caller should allocate memory for the struct RelCatEntry before calling the function.

Arguments

Name	Type	Description
relId	`int`	The relation id of the relation in the Relation Cache Table
relCatBuf	`RelCatEntry*`	Pointer to struct RelCatEntry to which the Relation Catalog entry corresponding to input relId is to be copied

Return Values

Value	Description
`SUCCESS`	Successfully copied the Relation Catalog entry
`E_OUTOFBOUND`	Input relId is outside the valid set of possible relation ids
`E_RELNOTOPEN`	Entry corresponding to input relId is free in the Relation Cache Table.

Algorithm

int RelCacheTable::getRelCatEntry(int relId, RelCatEntry *relCatBuf) {

  if(/*relId is outside the range [0, MAX_OPEN-1]*/) {
    return E_OUTOFBOUND;
  }

  if(/*entry corresponding to the relId in the Relation Cache Table is free*/) {
    return E_RELNOTOPEN;
  }

  // copy the corresponding Relation Catalog entry in the Relation Cache Table
  // to relCatBuf.

  return SUCCESS;
}

RelCacheTable :: setRelCatEntry

Description

Sets the Relation Catalog entry corresponding to the specified relation in the Relation Cache Table.

note

The caller should allocate memory for the struct RelCatEntry before calling the function.

Arguments

Name	Type	Description
relId	`int`	The relation id of the relation in the Relation Cache Table
relCatBuf	`RelCatEntry*`	Pointer to struct RelCatEntry using which the Relation Catalog entry corresponding to input relId is to be updated

Return Values

Value	Description
`SUCCESS`	Successfully copied the Relation Catalog entry
`E_OUTOFBOUND`	Input relId is outside the valid set of possible relation ids
`E_RELNOTOPEN`	Entry corresponding to input relId is free in the Relation Cache Table.

Algorithm

int RelCacheTable::setRelCatEntry(int relId, RelCatEntry *relCatBuf) {

  if(/*relId is outside the range [0, MAX_OPEN-1]*/) {
    return E_OUTOFBOUND;
  }

  if(/*entry corresponding to the relId in the Relation Cache Table is free*/) {
    return E_RELNOTOPEN;
  }

  // copy the relCatBuf to the corresponding Relation Catalog entry in
  // the Relation Cache Table.

  // set the dirty flag of the corresponding Relation Cache entry in
  // the Relation Cache Table.

  return SUCCESS;
}

RelCacheTable :: getSearchIndex

Description

Gives the value of searchIndex field of the given relation from Relation Cache Table. This is used by the linear search algorithm to find the location of the previous hit so that the search can be resumed from the next record.

note

The caller should allocate memory for the struct RecId before calling the function.

Arguments

Name	Type	Description
relId	`int`	The relation id of the relation in the Relation Cache Table
searchIndex	`RecId*`	Pointer to struct RecId to which the searchIndex field of the Relation Cache entry corresponding to input relId is to be copied

Return Values

Value	Description
`SUCCESS`	Successfully copied the search index to the argument.
`E_OUTOFBOUND`	Input relId is outside the valid set of possible relation ids
`E_RELNOTOPEN`	Entry corresponding to input relId is free in the Relation Cache Table.

Algorithm

int relCacheTable::getSearchIndex(int relid, recId *recidbuff_ptr) {

  if(/*relId is outside the range [0, MAX_OPEN-1]*/) {
    return E_OUTOFBOUND;
  }

  if(/*entry corresponding to the relId in the Relation Cache Table is free*/) {
    return E_RELNOTOPEN;
  }

  // copy the searchIndex field of the Relation Cache entry corresponding to
  // input relId to searchIndex variable.

  return SUCCESS;
}

RelCacheTable :: setSearchIndex

Description

Sets the value of searchIndex field of the given relation in Relation Cache Table. This is used by the linear search algorithm to set the location of the previous hit so that the search can be resumed from the next record.

note

The value of the search index is expected to be verified by the caller. This function does not check the validity of the search index before setting it into the cache entry.

Arguments

Name	Type	Description
relId	`int`	The relation id of the relation in the Relation Cache Table
searchIndex	`RecId*`	Pointer to struct RecId using which the searchIndex field of the Relation Cache entry corresponding to input relId is to be updated

Return Values

Value	Description
`SUCCESS`	Successfully set the search index in the relation cache
`E_OUTOFBOUND`	Input relId is outside the valid set of possible relation ids
`E_RELNOTOPEN`	Entry corresponding to input relId is free in the Relation Cache Table.

Algorithm

int RelCacheTable::setSearchIndex(int relId, recId *searchIndex) {

  if(/*relId is outside the range [0, MAX_OPEN-1]*/) {
    return E_OUTOFBOUND;
  }

  if(/*entry corresponding to the relId in the Relation Cache Table is free*/) {
    return E_RELNOTOPEN;
  }

  // copy the searchIndex variable to the searchIndex field of the Relation
  // Cache entry corresponding to input relId.

  return SUCCESS;
}

RelCacheTable :: resetSearchIndex

Description

Resets the value of searchIndex field of the given relation in Relation Cache Table to {-1, -1}. This is used so that the linear search can be restarted from the first record.

Arguments

Name	Type	Description
relId	`int`	The relation id of the relation in the Relation Cache Table

Return Values

Value	Description
`SUCCESS`	Successfully reset the search index in the relation cache.
`E_OUTOFBOUND`	Input relId is outside the valid set of possible relation ids
`E_RELNOTOPEN`	Entry corresponding to input relId is free in the Relation Cache Table.

Algorithm

int RelCacheTable::resetSearchIndex(int relId) {

  // declare a RecId having value {-1, -1}
  // set the search index to {-1, -1} using RelCacheTable::setSearchIndex
  // return the value returned by setSearchIndex
}

RelCacheTable :: recordToRelCatEntry

Description

A utility function that converts a record, implemented as an array of union Attribute, to RelCatEntry structure. This function can be used to convert a record in a Relation Catalog block to the corresponding Relation Cache entry when caching a relation in Relation Cache Table. The details of the implementation are left to you.

note

The caller should allocate memory for the struct RelCatEntry and array of union Attribute before calling the function.

Arguments

Name	Type	Description
record	`union Attribute[RELCAT_SIZE`]	The record which is to be converted to a `RelCatEntry`
RelCatEntry	`RelCatEntry*`	Pointer to struct `RelCatEntry` to which the contents of the input record is to be copied

Return Values

Nil

RelCacheTable :: relCatEntryToRecord

Description

A utility function that converts RelCatEntry structure to a record, implemented as an array of union Attribute. This function can be used to convert the Relation Cache entry to the corresponding record that can be written back to Relation Catalog block when closing a relation in the cache memory. The details of the implementation are left to you.

note

The caller should allocate memory for the struct RelCatEntry and array of union Attribute before calling the function.

Arguments

Name	Type	Description
RelCatEntry	`RelCatEntry*`	Pointer to struct `RelCatEntry` which is to be converted to a record.
record	`union Attribute[RELCAT_SIZE]`	The record to which the contents of the input `RelCatEntry` is to be copied

Return Values

Nil

RelCacheTable :: getRelCatEntry​

Description​

Arguments​

Return Values​

Algorithm​

RelCacheTable :: setRelCatEntry​

Description​

Arguments​

Return Values​

Algorithm​

RelCacheTable :: getSearchIndex​

Description​

Arguments​

Return Values​

Algorithm​

RelCacheTable :: setSearchIndex​

Description​

Arguments​

Return Values​

Algorithm​

RelCacheTable :: resetSearchIndex​

Description​

Arguments​

Return Values​

Algorithm​

RelCacheTable :: recordToRelCatEntry​

Description​

Arguments​

Return Values​

RelCacheTable :: relCatEntryToRecord​

Description​

Arguments​

Return Values​

RelCacheTable :: getRelCatEntry

Description

Arguments

Return Values

Algorithm

RelCacheTable :: setRelCatEntry

Description

Arguments

Return Values

Algorithm

RelCacheTable :: getSearchIndex

Description

Arguments

Return Values

Algorithm

RelCacheTable :: setSearchIndex

Description

Arguments

Return Values

Algorithm

RelCacheTable :: resetSearchIndex

Description

Arguments

Return Values

Algorithm

RelCacheTable :: recordToRelCatEntry

Description

Arguments

Return Values

RelCacheTable :: relCatEntryToRecord

Description

Arguments

Return Values