Table C (File architecture) - Revision history

ELowell at 22:29, 13 April 2015

2015-04-13T22:29:10Z

← Older revision		Revision as of 22:29, 13 April 2015
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	<p> Any time a field (whether preallocated or a [[Field value pairs (File architecture)\|field value pair]]) that has the <var>KEY</var> or <var>NUMERIC RANGE</var> attribute is added to a record, the hashing algorithm is used to find a Property entry. If it is not found it is created.</p>		<p> Any time a field (whether preallocated or a [[Field value pairs (File architecture)\|field value pair]]) that has the <var>KEY</var> or <var>NUMERIC RANGE</var> attribute is added to a record, the hashing algorithm is used to find a Property entry. If it is not found it is created.</p>

	<p>New <var>KEY</var> values require only two slots in Table C for an initial creation (one Property and one Segment entry). If the file size multiplier (discussed in [[File size calculation#Computing the file size multiplier (N)\|Computing the file size multiplier (N)]]) is greater than 1 (signifying the number of segments in the file), <var>KEY</var> values might require more than two slots. Therefore, at a rate dependent upon the level and nature of update activity, the number of slots used increases.</p>		<p>New <var>KEY</var> values require only two slots in Table C for an initial creation (one Property and one Segment entry). If the file size multiplier (discussed in [[File size calculation in detail#Computing the file size multiplier (N)\|Computing the file size multiplier (N)]]) is greater than 1 (signifying the number of segments in the file), <var>KEY</var> values might require more than two slots. Therefore, at a rate dependent upon the level and nature of update activity, the number of slots used increases.</p>

	<p>The chain is read (or created) to find the Segment entry covering the record being updated.</p>		<p>The chain is read (or created) to find the Segment entry covering the record being updated.</p>

JAL at 23:59, 24 January 2014

2014-01-24T23:59:40Z

← Older revision		Revision as of 23:59, 24 January 2014
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	<p>Table C is a hashed table divided into entries of seven bytes each. Table C		<p>Table C is a hashed table divided into entries of seven bytes each. Table C
	entries store index information for fields that have the KEY or the NUMERIC		entries store index information for fields that have the <var>KEY</var> or the <var>NUMERIC
	RANGE ~~attributes~~.</p>		RANGE</var> attribute.</p>

	<p>This page discusses the architecture underlying Table C. For information on monitoring, tuning and performance issues, refer to [[Tuning the hash index]].</p>		<p>This page discusses the architecture underlying Table C. For information on monitoring, tuning, and performance issues, refer to [[Tuning the hash index]].</p>

	== Overview ==		==Overview==
	<p> Model 204 creates a chain of entries in Table C for each value stored in a KEY field and several chains of entries for each value stored in a NUMERIC RANGE field.</p>		<p>
			Model 204 creates a chain of entries in Table C for each value stored in a <var>KEY</var> field, and several chains of entries for each value stored in a <var>NUMERIC RANGE</var> field.</p>

	<p> Any time a field (whether preallocated or a [[Field value pairs (File architecture)\|field value pair]]) that has the KEY or NUMERIC ~~range attributes~~ is added to a record, the hashing algorithm is used to find a Property ~~Entry~~. If it is not found it is created.</p>		<p> Any time a field (whether preallocated or a [[Field value pairs (File architecture)\|field value pair]]) that has the <var>KEY</var> or <var>NUMERIC RANGE</var> attribute is added to a record, the hashing algorithm is used to find a Property entry. If it is not found it is created.</p>

	<p>New KEY values require only two slots in Table C for an initial creation (one Property and one Segment entry). If the file size multiplier (discussed in [[File size calculation#Computing the file size multiplier (N)\|Computing the file size multiplier (N)]]) is greater than 1 (signifying the number of segments in the file), KEY values might require more than two slots. Therefore, at a rate dependent upon the level and nature of update activity, the number of slots used increases.</p>		<p>New <var>KEY</var> values require only two slots in Table C for an initial creation (one Property and one Segment entry). If the file size multiplier (discussed in [[File size calculation#Computing the file size multiplier (N)\|Computing the file size multiplier (N)]]) is greater than 1 (signifying the number of segments in the file), <var>KEY</var> values might require more than two slots. Therefore, at a rate dependent upon the level and nature of update activity, the number of slots used increases.</p>

	<p>The chain is read (or created) to find the Segment ~~Entry~~ covering the record being updated.</p>		<p>The chain is read (or created) to find the Segment entry covering the record being updated.</p>

	<p>Because of the hashed nature of the contents, Table C may not be increased dynamically. Any changes must be done via a [[File reorganization and table compaction\|reorganization]].</p>		<p>Because of the hashed nature of the contents, Table C may not be increased dynamically. Any changes must be done via a [[File reorganization and table compaction\|reorganization]].</p>

	== Table C ~~Page Structure~~ ==		==Table C page structure==
			<p>
			Every Table C page is composed of a series of 7-byte hash cells (a total of 877 per page). It also contains 5 bytes used to track "spills" (cases where the entry cannot be placed on the page to which the field/value hashes).</p>

	<p>~~Every Table C page is composed of a series of 7 byte~~ hash cells ~~(a total~~ of ~~877 per page). It also contains 5 bytes used to track 'spills' (cases where the~~ entry ~~can not be placed on the page that the field / value hashes to)~~.</p>		<p>The hash cells contain one of two types of entry: property and segment.</p>

	<p>~~The~~ hash ~~cells contain one~~ of ~~two types of entry: Property, and Segment~~.</p>		==Property entries==
			<p>
			A property entry is the starting point of a chain. When reading or updating a hash index, this is the location to which the field/value hashes in. From there, the chain of segment entries are read.</p>

	== ~~Property Entries~~ ==		==Segment entries==
	<p>~~The starting point~~ of ~~a chain~~.</p>		<p>
			Chained from the property entry are one or more segment entries (see the definition of segment, which follows).</p>

	<p>~~When reading or updating a hash index~~, ~~this~~ is the ~~location~~ the ~~field / value hashes~~ in ~~to. From there,~~ the ~~chain of segment entries are read~~.~~</p>~~		<p>Segment entries have two possible references to records:</p>
			<ul>
			<li>If the segment contains one and only one record with that combination of field and value, there is a direct pointer to the record (the [[Table B (File architecture)#Internal Record Number\|Internal Record Number (IRN)]] is physically stored in the Table C entry).

	~~== Segment Entries ==~~		<li>Otherwise, the segment points to a [[Table D (File architecture)#List and bitmap pages\|list or bitmap page]].
			</ul>
	~~<p>Chained from the Property Entry are one or more segment entries (see the definition of segment which follows).</p>~~

	~~<p>In the segment entries, there are two possible references to records:~~</p>

	* If, in the segment, there is one and only one record with that combination of field and value, there is a direct pointer to the record (the [[Table B (File architecture)#Internal Record Number\|Internal Record Number (IRN)]] is physically stored in the Table C entry).
	* Otherwise, the segment ~~will point~~ to a [[Table D (File architecture)#List and bitmap pages\|list or bitmap page]].

	It is quite possible that, for a particular field / value, some of the segment pointers will directly point to records; others will point to list or bitmap pages; and some segments, where no records will have the value for this field, will not have an occurrence in the chain at all.

	~~=== Segment definition ===~~

	<p>A segment is a set of 49152 base record slots. This 'magic' number comes from the number of bits which fit on a Model 204 page (see [[Table D (File architecture)#List and bitmap pages\|List and bitmap pages]]).</p>

			It is quite possible that, for a particular field/value, some of the segment pointers directly point to records; others point to list or bitmap pages; and some segments, where no records have the value for this field, have no occurrence in the chain at all.

			===Segment definition===
			<p>
			A segment is a set of 49152 base record slots. This "magic" number comes from the number of bits that fit on a Model 204 page (see [[Table D (File architecture)#List and bitmap pages\|List and bitmap pages]]).</p>

	[[Category:File architecture]]		[[Category:File architecture]]

Admin: Admin moved page Table C (File Architecture) to Table C (File architecture) without leaving a redirect

2013-12-18T22:21:57Z

Admin moved page Table C (File Architecture) to Table C (File architecture) without leaving a redirect

← Older revision	Revision as of 22:21, 18 December 2013
(No difference)

Admin at 22:18, 18 December 2013

2013-12-18T22:18:48Z

← Older revision		Revision as of 22:18, 18 December 2013
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	<p>In the segment entries, there are two possible references to records:</p>		<p>In the segment entries, there are two possible references to records:</p>

	* If, in the segment, there is one and only one record with that combination of field and value, there is a direct pointer to the record (the [[Table B (File ~~Architecture~~)#Internal Record Number\|Internal Record Number (IRN)]] is physically stored in the Table C entry).		* If, in the segment, there is one and only one record with that combination of field and value, there is a direct pointer to the record (the [[Table B (File architecture)#Internal Record Number\|Internal Record Number (IRN)]] is physically stored in the Table C entry).
	* Otherwise, the segment will point to a [[Table D (File architecture)#List and bitmap pages\|list or bitmap page]].		* Otherwise, the segment will point to a [[Table D (File architecture)#List and bitmap pages\|list or bitmap page]].

Admin at 21:58, 18 December 2013

2013-12-18T21:58:40Z

← Older revision		Revision as of 21:58, 18 December 2013
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	<p> Model 204 creates a chain of entries in Table C for each value stored in a KEY field and several chains of entries for each value stored in a NUMERIC RANGE field.</p>		<p> Model 204 creates a chain of entries in Table C for each value stored in a KEY field and several chains of entries for each value stored in a NUMERIC RANGE field.</p>

	<p> Any time a field (whether preallocated or a [[Field ~~Value Pairs~~ (File ~~Architecture~~)\|~~Field Value Pair~~]]) that has the KEY or NUMERIC range attributes is added to a record, the hashing algorithm is used to find a Property Entry. If it is not found it is created.</p>		<p> Any time a field (whether preallocated or a [[Field value pairs (File architecture)\|field value pair]]) that has the KEY or NUMERIC range attributes is added to a record, the hashing algorithm is used to find a Property Entry. If it is not found it is created.</p>

	<p>New KEY values require only two slots in Table C for an initial creation (one Property and one Segment entry). If the file size multiplier (discussed in [[File size calculation#Computing the file size multiplier (N)\|Computing the file size multiplier (N)]]) is greater than 1 (signifying the number of segments in the file), KEY values might require more than two slots. Therefore, at a rate dependent upon the level and nature of update activity, the number of slots used increases.</p>		<p>New KEY values require only two slots in Table C for an initial creation (one Property and one Segment entry). If the file size multiplier (discussed in [[File size calculation#Computing the file size multiplier (N)\|Computing the file size multiplier (N)]]) is greater than 1 (signifying the number of segments in the file), KEY values might require more than two slots. Therefore, at a rate dependent upon the level and nature of update activity, the number of slots used increases.</p>

Admin at 21:42, 18 December 2013

2013-12-18T21:42:56Z

← Older revision		Revision as of 21:42, 18 December 2013
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	* If, in the segment, there is one and only one record with that combination of field and value, there is a direct pointer to the record (the [[Table B (File Architecture)#Internal Record Number\|Internal Record Number (IRN)]] is physically stored in the Table C entry).		* If, in the segment, there is one and only one record with that combination of field and value, there is a direct pointer to the record (the [[Table B (File Architecture)#Internal Record Number\|Internal Record Number (IRN)]] is physically stored in the Table C entry).
	* Otherwise, the segment will point to a [[Table D (File ~~Architecture~~)#List and ~~Bit Map~~ pages\|list or bitmap page]].		* Otherwise, the segment will point to a [[Table D (File architecture)#List and bitmap pages\|list or bitmap page]].

	It is quite possible that, for a particular field / value, some of the segment pointers will directly point to records; others will point to list or bitmap pages; and some segments, where no records will have the value for this field, will not have an occurrence in the chain at all.		It is quite possible that, for a particular field / value, some of the segment pointers will directly point to records; others will point to list or bitmap pages; and some segments, where no records will have the value for this field, will not have an occurrence in the chain at all.
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	=== Segment definition ===		=== Segment definition ===

	<p>A segment is a set of 49152 base record slots. This 'magic' number comes from the number of bits which fit on a Model 204 page (see [[Table D (File ~~Architecture~~)#List and ~~Bit Map Pages~~\|List and ~~Bit Map~~ pages]]).</p>		<p>A segment is a set of 49152 base record slots. This 'magic' number comes from the number of bits which fit on a Model 204 page (see [[Table D (File architecture)#List and bitmap pages\|List and bitmap pages]]).</p>



	[[Category:File architecture]]		[[Category:File architecture]]

ELowell at 21:23, 12 December 2013

2013-12-12T21:23:34Z

← Older revision		Revision as of 21:23, 12 December 2013
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	<p>The chain is read (or created) to find the Segment Entry covering the record being updated.</p>		<p>The chain is read (or created) to find the Segment Entry covering the record being updated.</p>

	<p>Because of the hashed nature of the contents, Table C may not be increased dynamically. Any changes must be done via a [[File ~~Reorganization~~ and ~~Table Compaction~~\|reorganization]].</p>		<p>Because of the hashed nature of the contents, Table C may not be increased dynamically. Any changes must be done via a [[File reorganization and table compaction\|reorganization]].</p>

	== Table C Page Structure ==		== Table C Page Structure ==

ELowell at 19:14, 12 December 2013

2013-12-12T19:14:04Z

← Older revision		Revision as of 19:14, 12 December 2013
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	<p> Any time a field (whether preallocated or a [[Field Value Pairs (File Architecture)\|Field Value Pair]]) that has the KEY or NUMERIC range attributes is added to a record, the hashing algorithm is used to find a Property Entry. If it is not found it is created.</p>		<p> Any time a field (whether preallocated or a [[Field Value Pairs (File Architecture)\|Field Value Pair]]) that has the KEY or NUMERIC range attributes is added to a record, the hashing algorithm is used to find a Property Entry. If it is not found it is created.</p>

	<p>New KEY values require only two slots in Table C for an initial creation (one Property and one Segment entry). If the file size multiplier (discussed in [[File ~~Size Calculation~~#Computing the file size multiplier (N)\|Computing the file size multiplier (N)]]) is greater than 1 (signifying the number of segments in the file), KEY values might require more than two slots. Therefore, at a rate dependent upon the level and nature of update activity, the number of slots used increases.</p>		<p>New KEY values require only two slots in Table C for an initial creation (one Property and one Segment entry). If the file size multiplier (discussed in [[File size calculation#Computing the file size multiplier (N)\|Computing the file size multiplier (N)]]) is greater than 1 (signifying the number of segments in the file), KEY values might require more than two slots. Therefore, at a rate dependent upon the level and nature of update activity, the number of slots used increases.</p>

	<p>The chain is read (or created) to find the Segment Entry covering the record being updated.</p>		<p>The chain is read (or created) to find the Segment Entry covering the record being updated.</p>

ELowell: /* Property Entries */

2013-08-21T22:28:31Z

Property Entries

← Older revision		Revision as of 22:28, 21 August 2013
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	<p>The starting point of a chain.</p>		<p>The starting point of a chain.</p>

	<p>When reading or updating a hash index, this is the location the field / value hashes in to. From there, the chain of segment entries are read.</p>		<p>When reading or updating a hash index, this is the location the field / value hashes in to. From there, the chain of segment entries are read.</p>



	== Segment Entries ==		== Segment Entries ==

ELowell: /* Overview */

2013-08-21T22:28:19Z

Overview

← Older revision		Revision as of 22:28, 21 August 2013
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	<p>New KEY values require only two slots in Table C for an initial creation (one Property and one Segment entry). If the file size multiplier (discussed in [[File Size Calculation#Computing the file size multiplier (N)\|Computing the file size multiplier (N)]]) is greater than 1 (signifying the number of segments in the file), KEY values might require more than two slots. Therefore, at a rate dependent upon the level and nature of update activity, the number of slots used increases.</p>		<p>New KEY values require only two slots in Table C for an initial creation (one Property and one Segment entry). If the file size multiplier (discussed in [[File Size Calculation#Computing the file size multiplier (N)\|Computing the file size multiplier (N)]]) is greater than 1 (signifying the number of segments in the file), KEY values might require more than two slots. Therefore, at a rate dependent upon the level and nature of update activity, the number of slots used increases.</p>


	<p>The chain is read (or created) to find the Segment Entry covering the record being updated.</p>		<p>The chain is read (or created) to find the Segment Entry covering the record being updated.</p>

	<p>Because of the hashed nature of the contents, Table C may not be increased dynamically. Any changes must be done via a [[File Reorganization and Table Compaction\|reorganization]].</p>		<p>Because of the hashed nature of the contents, Table C may not be increased dynamically. Any changes must be done via a [[File Reorganization and Table Compaction\|reorganization]].</p>

	== Table C Page Structure ==		== Table C Page Structure ==