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diff --git a/doc/src/sgml/html/spgist-extensibility.html b/doc/src/sgml/html/spgist-extensibility.html new file mode 100644 index 0000000..184f57b --- /dev/null +++ b/doc/src/sgml/html/spgist-extensibility.html @@ -0,0 +1,597 @@ +<?xml version="1.0" encoding="UTF-8" standalone="no"?> +<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"><html xmlns="http://www.w3.org/1999/xhtml"><head><meta http-equiv="Content-Type" content="text/html; charset=UTF-8" /><title>65.3. Extensibility</title><link rel="stylesheet" type="text/css" href="stylesheet.css" /><link rev="made" href="pgsql-docs@lists.postgresql.org" /><meta name="generator" content="DocBook XSL Stylesheets V1.79.1" /><link rel="prev" href="spgist-builtin-opclasses.html" title="65.2. Built-in Operator Classes" /><link rel="next" href="spgist-implementation.html" title="65.4. Implementation" /></head><body id="docContent" class="container-fluid col-10"><div xmlns="http://www.w3.org/TR/xhtml1/transitional" class="navheader"><table width="100%" summary="Navigation header"><tr><th colspan="5" align="center">65.3. Extensibility</th></tr><tr><td width="10%" align="left"><a accesskey="p" href="spgist-builtin-opclasses.html" title="65.2. Built-in Operator Classes">Prev</a> </td><td width="10%" align="left"><a accesskey="u" href="spgist.html" title="Chapter 65. SP-GiST Indexes">Up</a></td><th width="60%" align="center">Chapter 65. SP-GiST Indexes</th><td width="10%" align="right"><a accesskey="h" href="index.html" title="PostgreSQL 13.4 Documentation">Home</a></td><td width="10%" align="right"> <a accesskey="n" href="spgist-implementation.html" title="65.4. Implementation">Next</a></td></tr></table><hr></hr></div><div class="sect1" id="SPGIST-EXTENSIBILITY"><div class="titlepage"><div><div><h2 class="title" style="clear: both">65.3. Extensibility</h2></div></div></div><p> + <acronym class="acronym">SP-GiST</acronym> offers an interface with a high level of + abstraction, requiring the access method developer to implement only + methods specific to a given data type. The <acronym class="acronym">SP-GiST</acronym> core + is responsible for efficient disk mapping and searching the tree structure. + It also takes care of concurrency and logging considerations. + </p><p> + Leaf tuples of an <acronym class="acronym">SP-GiST</acronym> tree contain values of the + same data type as the indexed column. Leaf tuples at the root level will + always contain the original indexed data value, but leaf tuples at lower + levels might contain only a compressed representation, such as a suffix. + In that case the operator class support functions must be able to + reconstruct the original value using information accumulated from the + inner tuples that are passed through to reach the leaf level. + </p><p> + Inner tuples are more complex, since they are branching points in the + search tree. Each inner tuple contains a set of one or more + <em class="firstterm">nodes</em>, which represent groups of similar leaf values. + A node contains a downlink that leads either to another, lower-level inner + tuple, or to a short list of leaf tuples that all lie on the same index page. + Each node normally has a <em class="firstterm">label</em> that describes it; for example, + in a radix tree the node label could be the next character of the string + value. (Alternatively, an operator class can omit the node labels, if it + works with a fixed set of nodes for all inner tuples; + see <a class="xref" href="spgist-implementation.html#SPGIST-NULL-LABELS" title="65.4.2. SP-GiST Without Node Labels">Section 65.4.2</a>.) + Optionally, an inner tuple can have a <em class="firstterm">prefix</em> value + that describes all its members. In a radix tree this could be the common + prefix of the represented strings. The prefix value is not necessarily + really a prefix, but can be any data needed by the operator class; + for example, in a quad-tree it can store the central point that the four + quadrants are measured with respect to. A quad-tree inner tuple would + then also contain four nodes corresponding to the quadrants around this + central point. + </p><p> + Some tree algorithms require knowledge of level (or depth) of the current + tuple, so the <acronym class="acronym">SP-GiST</acronym> core provides the possibility for + operator classes to manage level counting while descending the tree. + There is also support for incrementally reconstructing the represented + value when that is needed, and for passing down additional data (called + <em class="firstterm">traverse values</em>) during a tree descent. + </p><div class="note"><h3 class="title">Note</h3><p> + The <acronym class="acronym">SP-GiST</acronym> core code takes care of null entries. + Although <acronym class="acronym">SP-GiST</acronym> indexes do store entries for nulls + in indexed columns, this is hidden from the index operator class code: + no null index entries or search conditions will ever be passed to the + operator class methods. (It is assumed that <acronym class="acronym">SP-GiST</acronym> + operators are strict and so cannot succeed for null values.) Null values + are therefore not discussed further here. + </p></div><p> + There are five user-defined methods that an index operator class for + <acronym class="acronym">SP-GiST</acronym> must provide, and two are optional. All five + mandatory methods follow the convention of accepting two <code class="type">internal</code> + arguments, the first of which is a pointer to a C struct containing input + values for the support method, while the second argument is a pointer to a + C struct where output values must be placed. Four of the mandatory methods just + return <code class="type">void</code>, since all their results appear in the output struct; but + <code class="function">leaf_consistent</code> returns a <code class="type">boolean</code> result. + The methods must not modify any fields of their input structs. In all + cases, the output struct is initialized to zeroes before calling the + user-defined method. The optional sixth method <code class="function">compress</code> + accepts a <code class="type">datum</code> to be indexed as the only argument and returns a value suitable + for physical storage in a leaf tuple. The optional seventh method + <code class="function">options</code> accepts an <code class="type">internal</code> pointer to a C struct, where + opclass-specific parameters should be placed, and returns <code class="type">void</code>. + </p><p> + The five mandatory user-defined methods are: + </p><div class="variablelist"><dl class="variablelist"><dt><span class="term"><code class="function">config</code></span></dt><dd><p> + Returns static information about the index implementation, including + the data type OIDs of the prefix and node label data types. + </p><p> + The <acronym class="acronym">SQL</acronym> declaration of the function must look like this: +</p><pre class="programlisting"> +CREATE FUNCTION my_config(internal, internal) RETURNS void ... +</pre><p> + The first argument is a pointer to a <code class="structname">spgConfigIn</code> + C struct, containing input data for the function. + The second argument is a pointer to a <code class="structname">spgConfigOut</code> + C struct, which the function must fill with result data. +</p><pre class="programlisting"> +typedef struct spgConfigIn +{ + Oid attType; /* Data type to be indexed */ +} spgConfigIn; + +typedef struct spgConfigOut +{ + Oid prefixType; /* Data type of inner-tuple prefixes */ + Oid labelType; /* Data type of inner-tuple node labels */ + Oid leafType; /* Data type of leaf-tuple values */ + bool canReturnData; /* Opclass can reconstruct original data */ + bool longValuesOK; /* Opclass can cope with values > 1 page */ +} spgConfigOut; +</pre><p> + + <code class="structfield">attType</code> is passed in order to support polymorphic + index operator classes; for ordinary fixed-data-type operator classes, it + will always have the same value and so can be ignored. + </p><p> + For operator classes that do not use prefixes, + <code class="structfield">prefixType</code> can be set to <code class="literal">VOIDOID</code>. + Likewise, for operator classes that do not use node labels, + <code class="structfield">labelType</code> can be set to <code class="literal">VOIDOID</code>. + <code class="structfield">canReturnData</code> should be set true if the operator class + is capable of reconstructing the originally-supplied index value. + <code class="structfield">longValuesOK</code> should be set true only when the + <code class="structfield">attType</code> is of variable length and the operator + class is capable of segmenting long values by repeated suffixing + (see <a class="xref" href="spgist-implementation.html#SPGIST-LIMITS" title="65.4.1. SP-GiST Limits">Section 65.4.1</a>). + </p><p> + <code class="structfield">leafType</code> is typically the same as + <code class="structfield">attType</code>. For the reasons of backward + compatibility, method <code class="function">config</code> can + leave <code class="structfield">leafType</code> uninitialized; that would + give the same effect as setting <code class="structfield">leafType</code> equal + to <code class="structfield">attType</code>. When <code class="structfield">attType</code> + and <code class="structfield">leafType</code> are different, then optional + method <code class="function">compress</code> must be provided. + Method <code class="function">compress</code> is responsible + for transformation of datums to be indexed from <code class="structfield">attType</code> + to <code class="structfield">leafType</code>. + Note: both consistent functions will get <code class="structfield">scankeys</code> + unchanged, without transformation using <code class="function">compress</code>. + </p></dd><dt><span class="term"><code class="function">choose</code></span></dt><dd><p> + Chooses a method for inserting a new value into an inner tuple. + </p><p> + The <acronym class="acronym">SQL</acronym> declaration of the function must look like this: +</p><pre class="programlisting"> +CREATE FUNCTION my_choose(internal, internal) RETURNS void ... +</pre><p> + The first argument is a pointer to a <code class="structname">spgChooseIn</code> + C struct, containing input data for the function. + The second argument is a pointer to a <code class="structname">spgChooseOut</code> + C struct, which the function must fill with result data. +</p><pre class="programlisting"> +typedef struct spgChooseIn +{ + Datum datum; /* original datum to be indexed */ + Datum leafDatum; /* current datum to be stored at leaf */ + int level; /* current level (counting from zero) */ + + /* Data from current inner tuple */ + bool allTheSame; /* tuple is marked all-the-same? */ + bool hasPrefix; /* tuple has a prefix? */ + Datum prefixDatum; /* if so, the prefix value */ + int nNodes; /* number of nodes in the inner tuple */ + Datum *nodeLabels; /* node label values (NULL if none) */ +} spgChooseIn; + +typedef enum spgChooseResultType +{ + spgMatchNode = 1, /* descend into existing node */ + spgAddNode, /* add a node to the inner tuple */ + spgSplitTuple /* split inner tuple (change its prefix) */ +} spgChooseResultType; + +typedef struct spgChooseOut +{ + spgChooseResultType resultType; /* action code, see above */ + union + { + struct /* results for spgMatchNode */ + { + int nodeN; /* descend to this node (index from 0) */ + int levelAdd; /* increment level by this much */ + Datum restDatum; /* new leaf datum */ + } matchNode; + struct /* results for spgAddNode */ + { + Datum nodeLabel; /* new node's label */ + int nodeN; /* where to insert it (index from 0) */ + } addNode; + struct /* results for spgSplitTuple */ + { + /* Info to form new upper-level inner tuple with one child tuple */ + bool prefixHasPrefix; /* tuple should have a prefix? */ + Datum prefixPrefixDatum; /* if so, its value */ + int prefixNNodes; /* number of nodes */ + Datum *prefixNodeLabels; /* their labels (or NULL for + * no labels) */ + int childNodeN; /* which node gets child tuple */ + + /* Info to form new lower-level inner tuple with all old nodes */ + bool postfixHasPrefix; /* tuple should have a prefix? */ + Datum postfixPrefixDatum; /* if so, its value */ + } splitTuple; + } result; +} spgChooseOut; +</pre><p> + + <code class="structfield">datum</code> is the original datum of + <code class="structname">spgConfigIn</code>.<code class="structfield">attType</code> + type that was to be inserted into the index. + <code class="structfield">leafDatum</code> is a value of + <code class="structname">spgConfigOut</code>.<code class="structfield">leafType</code> + type, which is initially a result of method + <code class="function">compress</code> applied to <code class="structfield">datum</code> + when method <code class="function">compress</code> is provided, or the same value as + <code class="structfield">datum</code> otherwise. + <code class="structfield">leafDatum</code> can change at lower levels of the tree + if the <code class="function">choose</code> or <code class="function">picksplit</code> + methods change it. When the insertion search reaches a leaf page, + the current value of <code class="structfield">leafDatum</code> is what will be stored + in the newly created leaf tuple. + <code class="structfield">level</code> is the current inner tuple's level, starting at + zero for the root level. + <code class="structfield">allTheSame</code> is true if the current inner tuple is + marked as containing multiple equivalent nodes + (see <a class="xref" href="spgist-implementation.html#SPGIST-ALL-THE-SAME" title="65.4.3. “All-the-Same” Inner Tuples">Section 65.4.3</a>). + <code class="structfield">hasPrefix</code> is true if the current inner tuple contains + a prefix; if so, + <code class="structfield">prefixDatum</code> is its value. + <code class="structfield">nNodes</code> is the number of child nodes contained in the + inner tuple, and + <code class="structfield">nodeLabels</code> is an array of their label values, or + NULL if there are no labels. + </p><p> + The <code class="function">choose</code> function can determine either that + the new value matches one of the existing child nodes, or that a new + child node must be added, or that the new value is inconsistent with + the tuple prefix and so the inner tuple must be split to create a + less restrictive prefix. + </p><p> + If the new value matches one of the existing child nodes, + set <code class="structfield">resultType</code> to <code class="literal">spgMatchNode</code>. + Set <code class="structfield">nodeN</code> to the index (from zero) of that node in + the node array. + Set <code class="structfield">levelAdd</code> to the increment in + <code class="structfield">level</code> caused by descending through that node, + or leave it as zero if the operator class does not use levels. + Set <code class="structfield">restDatum</code> to equal <code class="structfield">leafDatum</code> + if the operator class does not modify datums from one level to the + next, or otherwise set it to the modified value to be used as + <code class="structfield">leafDatum</code> at the next level. + </p><p> + If a new child node must be added, + set <code class="structfield">resultType</code> to <code class="literal">spgAddNode</code>. + Set <code class="structfield">nodeLabel</code> to the label to be used for the new + node, and set <code class="structfield">nodeN</code> to the index (from zero) at which + to insert the node in the node array. + After the node has been added, the <code class="function">choose</code> + function will be called again with the modified inner tuple; + that call should result in an <code class="literal">spgMatchNode</code> result. + </p><p> + If the new value is inconsistent with the tuple prefix, + set <code class="structfield">resultType</code> to <code class="literal">spgSplitTuple</code>. + This action moves all the existing nodes into a new lower-level + inner tuple, and replaces the existing inner tuple with a tuple + having a single downlink pointing to the new lower-level inner tuple. + Set <code class="structfield">prefixHasPrefix</code> to indicate whether the new + upper tuple should have a prefix, and if so set + <code class="structfield">prefixPrefixDatum</code> to the prefix value. This new + prefix value must be sufficiently less restrictive than the original + to accept the new value to be indexed. + Set <code class="structfield">prefixNNodes</code> to the number of nodes needed in the + new tuple, and set <code class="structfield">prefixNodeLabels</code> to a palloc'd array + holding their labels, or to NULL if node labels are not required. + Note that the total size of the new upper tuple must be no more + than the total size of the tuple it is replacing; this constrains + the lengths of the new prefix and new labels. + Set <code class="structfield">childNodeN</code> to the index (from zero) of the node + that will downlink to the new lower-level inner tuple. + Set <code class="structfield">postfixHasPrefix</code> to indicate whether the new + lower-level inner tuple should have a prefix, and if so set + <code class="structfield">postfixPrefixDatum</code> to the prefix value. The + combination of these two prefixes and the downlink node's label + (if any) must have the same meaning as the original prefix, because + there is no opportunity to alter the node labels that are moved to + the new lower-level tuple, nor to change any child index entries. + After the node has been split, the <code class="function">choose</code> + function will be called again with the replacement inner tuple. + That call may return an <code class="literal">spgAddNode</code> result, if no suitable + node was created by the <code class="literal">spgSplitTuple</code> action. Eventually + <code class="function">choose</code> must return <code class="literal">spgMatchNode</code> to + allow the insertion to descend to the next level. + </p></dd><dt><span class="term"><code class="function">picksplit</code></span></dt><dd><p> + Decides how to create a new inner tuple over a set of leaf tuples. + </p><p> + The <acronym class="acronym">SQL</acronym> declaration of the function must look like this: +</p><pre class="programlisting"> +CREATE FUNCTION my_picksplit(internal, internal) RETURNS void ... +</pre><p> + The first argument is a pointer to a <code class="structname">spgPickSplitIn</code> + C struct, containing input data for the function. + The second argument is a pointer to a <code class="structname">spgPickSplitOut</code> + C struct, which the function must fill with result data. +</p><pre class="programlisting"> +typedef struct spgPickSplitIn +{ + int nTuples; /* number of leaf tuples */ + Datum *datums; /* their datums (array of length nTuples) */ + int level; /* current level (counting from zero) */ +} spgPickSplitIn; + +typedef struct spgPickSplitOut +{ + bool hasPrefix; /* new inner tuple should have a prefix? */ + Datum prefixDatum; /* if so, its value */ + + int nNodes; /* number of nodes for new inner tuple */ + Datum *nodeLabels; /* their labels (or NULL for no labels) */ + + int *mapTuplesToNodes; /* node index for each leaf tuple */ + Datum *leafTupleDatums; /* datum to store in each new leaf tuple */ +} spgPickSplitOut; +</pre><p> + + <code class="structfield">nTuples</code> is the number of leaf tuples provided. + <code class="structfield">datums</code> is an array of their datum values of + <code class="structname">spgConfigOut</code>.<code class="structfield">leafType</code> + type. + <code class="structfield">level</code> is the current level that all the leaf tuples + share, which will become the level of the new inner tuple. + </p><p> + Set <code class="structfield">hasPrefix</code> to indicate whether the new inner + tuple should have a prefix, and if so set + <code class="structfield">prefixDatum</code> to the prefix value. + Set <code class="structfield">nNodes</code> to indicate the number of nodes that + the new inner tuple will contain, and + set <code class="structfield">nodeLabels</code> to an array of their label values, + or to NULL if node labels are not required. + Set <code class="structfield">mapTuplesToNodes</code> to an array that gives the index + (from zero) of the node that each leaf tuple should be assigned to. + Set <code class="structfield">leafTupleDatums</code> to an array of the values to + be stored in the new leaf tuples (these will be the same as the + input <code class="structfield">datums</code> if the operator class does not modify + datums from one level to the next). + Note that the <code class="function">picksplit</code> function is + responsible for palloc'ing the + <code class="structfield">nodeLabels</code>, <code class="structfield">mapTuplesToNodes</code> and + <code class="structfield">leafTupleDatums</code> arrays. + </p><p> + If more than one leaf tuple is supplied, it is expected that the + <code class="function">picksplit</code> function will classify them into more than + one node; otherwise it is not possible to split the leaf tuples + across multiple pages, which is the ultimate purpose of this + operation. Therefore, if the <code class="function">picksplit</code> function + ends up placing all the leaf tuples in the same node, the core + SP-GiST code will override that decision and generate an inner + tuple in which the leaf tuples are assigned at random to several + identically-labeled nodes. Such a tuple is marked + <code class="literal">allTheSame</code> to signify that this has happened. The + <code class="function">choose</code> and <code class="function">inner_consistent</code> functions + must take suitable care with such inner tuples. + See <a class="xref" href="spgist-implementation.html#SPGIST-ALL-THE-SAME" title="65.4.3. “All-the-Same” Inner Tuples">Section 65.4.3</a> for more information. + </p><p> + <code class="function">picksplit</code> can be applied to a single leaf tuple only + in the case that the <code class="function">config</code> function set + <code class="structfield">longValuesOK</code> to true and a larger-than-a-page input + value has been supplied. In this case the point of the operation is + to strip off a prefix and produce a new, shorter leaf datum value. + The call will be repeated until a leaf datum short enough to fit on + a page has been produced. See <a class="xref" href="spgist-implementation.html#SPGIST-LIMITS" title="65.4.1. SP-GiST Limits">Section 65.4.1</a> for + more information. + </p></dd><dt><span class="term"><code class="function">inner_consistent</code></span></dt><dd><p> + Returns set of nodes (branches) to follow during tree search. + </p><p> + The <acronym class="acronym">SQL</acronym> declaration of the function must look like this: +</p><pre class="programlisting"> +CREATE FUNCTION my_inner_consistent(internal, internal) RETURNS void ... +</pre><p> + The first argument is a pointer to a <code class="structname">spgInnerConsistentIn</code> + C struct, containing input data for the function. + The second argument is a pointer to a <code class="structname">spgInnerConsistentOut</code> + C struct, which the function must fill with result data. + +</p><pre class="programlisting"> +typedef struct spgInnerConsistentIn +{ + ScanKey scankeys; /* array of operators and comparison values */ + ScanKey orderbys; /* array of ordering operators and comparison + * values */ + int nkeys; /* length of scankeys array */ + int norderbys; /* length of orderbys array */ + + Datum reconstructedValue; /* value reconstructed at parent */ + void *traversalValue; /* opclass-specific traverse value */ + MemoryContext traversalMemoryContext; /* put new traverse values here */ + int level; /* current level (counting from zero) */ + bool returnData; /* original data must be returned? */ + + /* Data from current inner tuple */ + bool allTheSame; /* tuple is marked all-the-same? */ + bool hasPrefix; /* tuple has a prefix? */ + Datum prefixDatum; /* if so, the prefix value */ + int nNodes; /* number of nodes in the inner tuple */ + Datum *nodeLabels; /* node label values (NULL if none) */ +} spgInnerConsistentIn; + +typedef struct spgInnerConsistentOut +{ + int nNodes; /* number of child nodes to be visited */ + int *nodeNumbers; /* their indexes in the node array */ + int *levelAdds; /* increment level by this much for each */ + Datum *reconstructedValues; /* associated reconstructed values */ + void **traversalValues; /* opclass-specific traverse values */ + double **distances; /* associated distances */ +} spgInnerConsistentOut; +</pre><p> + + The array <code class="structfield">scankeys</code>, of length <code class="structfield">nkeys</code>, + describes the index search condition(s). These conditions are + combined with AND — only index entries that satisfy all of + them are interesting. (Note that <code class="structfield">nkeys</code> = 0 implies + that all index entries satisfy the query.) Usually the consistent + function only cares about the <code class="structfield">sk_strategy</code> and + <code class="structfield">sk_argument</code> fields of each array entry, which + respectively give the indexable operator and comparison value. + In particular it is not necessary to check <code class="structfield">sk_flags</code> to + see if the comparison value is NULL, because the SP-GiST core code + will filter out such conditions. + The array <code class="structfield">orderbys</code>, of length <code class="structfield">norderbys</code>, + describes ordering operators (if any) in the same manner. + <code class="structfield">reconstructedValue</code> is the value reconstructed for the + parent tuple; it is <code class="literal">(Datum) 0</code> at the root level or if the + <code class="function">inner_consistent</code> function did not provide a value at the + parent level. <code class="structfield">reconstructedValue</code> is always of + <code class="structname">spgConfigOut</code>.<code class="structfield">leafType</code> type. + <code class="structfield">traversalValue</code> is a pointer to any traverse data + passed down from the previous call of <code class="function">inner_consistent</code> + on the parent index tuple, or NULL at the root level. + <code class="structfield">traversalMemoryContext</code> is the memory context in which + to store output traverse values (see below). + <code class="structfield">level</code> is the current inner tuple's level, starting at + zero for the root level. + <code class="structfield">returnData</code> is <code class="literal">true</code> if reconstructed data is + required for this query; this will only be so if the + <code class="function">config</code> function asserted <code class="structfield">canReturnData</code>. + <code class="structfield">allTheSame</code> is true if the current inner tuple is + marked <span class="quote">“<span class="quote">all-the-same</span>”</span>; in this case all the nodes have the + same label (if any) and so either all or none of them match the query + (see <a class="xref" href="spgist-implementation.html#SPGIST-ALL-THE-SAME" title="65.4.3. “All-the-Same” Inner Tuples">Section 65.4.3</a>). + <code class="structfield">hasPrefix</code> is true if the current inner tuple contains + a prefix; if so, + <code class="structfield">prefixDatum</code> is its value. + <code class="structfield">nNodes</code> is the number of child nodes contained in the + inner tuple, and + <code class="structfield">nodeLabels</code> is an array of their label values, or + NULL if the nodes do not have labels. + </p><p> + <code class="structfield">nNodes</code> must be set to the number of child nodes that + need to be visited by the search, and + <code class="structfield">nodeNumbers</code> must be set to an array of their indexes. + If the operator class keeps track of levels, set + <code class="structfield">levelAdds</code> to an array of the level increments + required when descending to each node to be visited. (Often these + increments will be the same for all the nodes, but that's not + necessarily so, so an array is used.) + If value reconstruction is needed, set + <code class="structfield">reconstructedValues</code> to an array of the values + of <code class="structname">spgConfigOut</code>.<code class="structfield">leafType</code> type + reconstructed for each child node to be visited; otherwise, leave + <code class="structfield">reconstructedValues</code> as NULL. + If ordered search is performed, set <code class="structfield">distances</code> + to an array of distance values according to <code class="structfield">orderbys</code> + array (nodes with lowest distances will be processed first). Leave it + NULL otherwise. + If it is desired to pass down additional out-of-band information + (<span class="quote">“<span class="quote">traverse values</span>”</span>) to lower levels of the tree search, + set <code class="structfield">traversalValues</code> to an array of the appropriate + traverse values, one for each child node to be visited; otherwise, + leave <code class="structfield">traversalValues</code> as NULL. + Note that the <code class="function">inner_consistent</code> function is + responsible for palloc'ing the + <code class="structfield">nodeNumbers</code>, <code class="structfield">levelAdds</code>, + <code class="structfield">distances</code>, + <code class="structfield">reconstructedValues</code>, and + <code class="structfield">traversalValues</code> arrays in the current memory context. + However, any output traverse values pointed to by + the <code class="structfield">traversalValues</code> array should be allocated + in <code class="structfield">traversalMemoryContext</code>. + Each traverse value must be a single palloc'd chunk. + </p></dd><dt><span class="term"><code class="function">leaf_consistent</code></span></dt><dd><p> + Returns true if a leaf tuple satisfies a query. + </p><p> + The <acronym class="acronym">SQL</acronym> declaration of the function must look like this: +</p><pre class="programlisting"> +CREATE FUNCTION my_leaf_consistent(internal, internal) RETURNS bool ... +</pre><p> + The first argument is a pointer to a <code class="structname">spgLeafConsistentIn</code> + C struct, containing input data for the function. + The second argument is a pointer to a <code class="structname">spgLeafConsistentOut</code> + C struct, which the function must fill with result data. +</p><pre class="programlisting"> +typedef struct spgLeafConsistentIn +{ + ScanKey scankeys; /* array of operators and comparison values */ + ScanKey orderbys; /* array of ordering operators and comparison + * values */ + int nkeys; /* length of scankeys array */ + int norderbys; /* length of orderbys array */ + + Datum reconstructedValue; /* value reconstructed at parent */ + void *traversalValue; /* opclass-specific traverse value */ + int level; /* current level (counting from zero) */ + bool returnData; /* original data must be returned? */ + + Datum leafDatum; /* datum in leaf tuple */ +} spgLeafConsistentIn; + +typedef struct spgLeafConsistentOut +{ + Datum leafValue; /* reconstructed original data, if any */ + bool recheck; /* set true if operator must be rechecked */ + bool recheckDistances; /* set true if distances must be rechecked */ + double *distances; /* associated distances */ +} spgLeafConsistentOut; +</pre><p> + + The array <code class="structfield">scankeys</code>, of length <code class="structfield">nkeys</code>, + describes the index search condition(s). These conditions are + combined with AND — only index entries that satisfy all of + them satisfy the query. (Note that <code class="structfield">nkeys</code> = 0 implies + that all index entries satisfy the query.) Usually the consistent + function only cares about the <code class="structfield">sk_strategy</code> and + <code class="structfield">sk_argument</code> fields of each array entry, which + respectively give the indexable operator and comparison value. + In particular it is not necessary to check <code class="structfield">sk_flags</code> to + see if the comparison value is NULL, because the SP-GiST core code + will filter out such conditions. + The array <code class="structfield">orderbys</code>, of length <code class="structfield">norderbys</code>, + describes the ordering operators in the same manner. + <code class="structfield">reconstructedValue</code> is the value reconstructed for the + parent tuple; it is <code class="literal">(Datum) 0</code> at the root level or if the + <code class="function">inner_consistent</code> function did not provide a value at the + parent level. <code class="structfield">reconstructedValue</code> is always of + <code class="structname">spgConfigOut</code>.<code class="structfield">leafType</code> type. + <code class="structfield">traversalValue</code> is a pointer to any traverse data + passed down from the previous call of <code class="function">inner_consistent</code> + on the parent index tuple, or NULL at the root level. + <code class="structfield">level</code> is the current leaf tuple's level, starting at + zero for the root level. + <code class="structfield">returnData</code> is <code class="literal">true</code> if reconstructed data is + required for this query; this will only be so if the + <code class="function">config</code> function asserted <code class="structfield">canReturnData</code>. + <code class="structfield">leafDatum</code> is the key value of + <code class="structname">spgConfigOut</code>.<code class="structfield">leafType</code> + stored in the current leaf tuple. + </p><p> + The function must return <code class="literal">true</code> if the leaf tuple matches the + query, or <code class="literal">false</code> if not. In the <code class="literal">true</code> case, + if <code class="structfield">returnData</code> is <code class="literal">true</code> then + <code class="structfield">leafValue</code> must be set to the value of + <code class="structname">spgConfigIn</code>.<code class="structfield">attType</code> type + originally supplied to be indexed for this leaf tuple. Also, + <code class="structfield">recheck</code> may be set to <code class="literal">true</code> if the match + is uncertain and so the operator(s) must be re-applied to the actual + heap tuple to verify the match. + If ordered search is performed, set <code class="structfield">distances</code> + to an array of distance values according to <code class="structfield">orderbys</code> + array. Leave it NULL otherwise. If at least one of returned distances + is not exact, set <code class="structfield">recheckDistances</code> to true. + In this case, the executor will calculate the exact distances after + fetching the tuple from the heap, and will reorder the tuples if needed. + </p></dd></dl></div><p> + The optional user-defined method are: + </p><div class="variablelist"><dl class="variablelist"><dt><span class="term"><code class="function">Datum compress(Datum in)</code></span></dt><dd><p> + Converts the data item into a format suitable for physical storage in + a leaf tuple of index page. It accepts + <code class="structname">spgConfigIn</code>.<code class="structfield">attType</code> + value and returns + <code class="structname">spgConfigOut</code>.<code class="structfield">leafType</code> + value. Output value should not be toasted. + </p></dd><dt><span class="term"><code class="function">options</code></span></dt><dd><p> + Defines a set of user-visible parameters that control operator class + behavior. + </p><p> + The <acronym class="acronym">SQL</acronym> declaration of the function must look like this: + +</p><pre class="programlisting"> +CREATE OR REPLACE FUNCTION my_options(internal) +RETURNS void +AS 'MODULE_PATHNAME' +LANGUAGE C STRICT; +</pre><p> + </p><p> + The function is passed a pointer to a <em class="replaceable"><code>local_relopts</code></em> + struct, which needs to be filled with a set of operator class + specific options. The options can be accessed from other support + functions using the <code class="literal">PG_HAS_OPCLASS_OPTIONS()</code> and + <code class="literal">PG_GET_OPCLASS_OPTIONS()</code> macros. + </p><p> + Since the representation of the key in <acronym class="acronym">SP-GiST</acronym> is + flexible, it may depend on user-specified parameters. + </p></dd></dl></div><p> + All the SP-GiST support methods are normally called in a short-lived + memory context; that is, <code class="varname">CurrentMemoryContext</code> will be reset + after processing of each tuple. It is therefore not very important to + worry about pfree'ing everything you palloc. (The <code class="function">config</code> + method is an exception: it should try to avoid leaking memory. But + usually the <code class="function">config</code> method need do nothing but assign + constants into the passed parameter struct.) + </p><p> + If the indexed column is of a collatable data type, the index collation + will be passed to all the support methods, using the standard + <code class="function">PG_GET_COLLATION()</code> mechanism. + </p></div><div xmlns="http://www.w3.org/TR/xhtml1/transitional" class="navfooter"><hr></hr><table width="100%" summary="Navigation footer"><tr><td width="40%" align="left"><a accesskey="p" href="spgist-builtin-opclasses.html" title="65.2. Built-in Operator Classes">Prev</a> </td><td width="20%" align="center"><a accesskey="u" href="spgist.html" title="Chapter 65. SP-GiST Indexes">Up</a></td><td width="40%" align="right"> <a accesskey="n" href="spgist-implementation.html" title="65.4. Implementation">Next</a></td></tr><tr><td width="40%" align="left" valign="top">65.2. 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