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><DIV
CLASS="SECT1"
><H1
CLASS="SECT1"
><A
NAME="SPGIST-EXTENSIBILITY"
>54.2. Extensibility</A
></H1
><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
<I
CLASS="FIRSTTERM"
>nodes</I
>, which represent groups of similar leaf values.
A node contains a downlink that leads to either another, lower-level inner
tuple, or a short list of leaf tuples that all lie on the same index page.
Each node has a <I
CLASS="FIRSTTERM"
>label</I
> that describes it; for example,
in a suffix tree the node label could be the next character of the string
value. Optionally, an inner tuple can have a <I
CLASS="FIRSTTERM"
>prefix</I
> value
that describes all its members. In a suffix 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.
</P
><DIV
CLASS="NOTE"
><BLOCKQUOTE
CLASS="NOTE"
><P
><B
>Note: </B
> 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
></BLOCKQUOTE
></DIV
><P
> There are five user-defined methods that an index operator class for
<ACRONYM
CLASS="ACRONYM"
>SP-GiST</ACRONYM
> must provide. All five follow the convention
of accepting two <TT
CLASS="TYPE"
>internal</TT
> 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 methods just return <TT
CLASS="TYPE"
>void</TT
>, since
all their results appear in the output struct; but
<CODE
CLASS="FUNCTION"
>leaf_consistent</CODE
> additionally returns a <TT
CLASS="TYPE"
>boolean</TT
> 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.
</P
><P
> The five user-defined methods are:
</P
><P
></P
><DIV
CLASS="VARIABLELIST"
><DL
><DT
><CODE
CLASS="FUNCTION"
>config</CODE
></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 <TT
CLASS="STRUCTNAME"
>spgConfigIn</TT
>
C struct, containing input data for the function.
The second argument is a pointer to a <TT
CLASS="STRUCTNAME"
>spgConfigOut</TT
>
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 */
bool canReturnData; /* Opclass can reconstruct original data */
bool longValuesOK; /* Opclass can cope with values > 1 page */
} spgConfigOut;</PRE
><P>
<TT
CLASS="STRUCTFIELD"
>attType</TT
> 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,
<TT
CLASS="STRUCTFIELD"
>prefixType</TT
> can be set to <TT
CLASS="LITERAL"
>VOIDOID</TT
>.
Likewise, for operator classes that do not use node labels,
<TT
CLASS="STRUCTFIELD"
>labelType</TT
> can be set to <TT
CLASS="LITERAL"
>VOIDOID</TT
>.
<TT
CLASS="STRUCTFIELD"
>canReturnData</TT
> should be set true if the operator class
is capable of reconstructing the originally-supplied index value.
<TT
CLASS="STRUCTFIELD"
>longValuesOK</TT
> should be set true only when the
<TT
CLASS="STRUCTFIELD"
>attType</TT
> is of variable length and the operator
class is capable of segmenting long values by repeated suffixing
(see <A
HREF="spgist-implementation.html#SPGIST-LIMITS"
>Section 54.3.1</A
>).
</P
></DD
><DT
><CODE
CLASS="FUNCTION"
>choose</CODE
></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 <TT
CLASS="STRUCTNAME"
>spgChooseIn</TT
>
C struct, containing input data for the function.
The second argument is a pointer to a <TT
CLASS="STRUCTNAME"
>spgChooseOut</TT
>
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 inner tuple with one node */
bool prefixHasPrefix; /* tuple should have a prefix? */
Datum prefixPrefixDatum; /* if so, its value */
Datum nodeLabel; /* node's label */
/* 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>
<TT
CLASS="STRUCTFIELD"
>datum</TT
> is the original datum that was to be inserted
into the index.
<TT
CLASS="STRUCTFIELD"
>leafDatum</TT
> is initially the same as
<TT
CLASS="STRUCTFIELD"
>datum</TT
>, but 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 <TT
CLASS="STRUCTFIELD"
>leafDatum</TT
> is what will be stored
in the newly created leaf tuple.
<TT
CLASS="STRUCTFIELD"
>level</TT
> is the current inner tuple's level, starting at
zero for the root level.
<TT
CLASS="STRUCTFIELD"
>allTheSame</TT
> is true if the current inner tuple is
marked as containing multiple equivalent nodes
(see <A
HREF="spgist-implementation.html#SPGIST-ALL-THE-SAME"
>Section 54.3.3</A
>).
<TT
CLASS="STRUCTFIELD"
>hasPrefix</TT
> is true if the current inner tuple contains
a prefix; if so,
<TT
CLASS="STRUCTFIELD"
>prefixDatum</TT
> is its value.
<TT
CLASS="STRUCTFIELD"
>nNodes</TT
> is the number of child nodes contained in the
inner tuple, and
<TT
CLASS="STRUCTFIELD"
>nodeLabels</TT
> 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 <TT
CLASS="STRUCTFIELD"
>resultType</TT
> to <TT
CLASS="LITERAL"
>spgMatchNode</TT
>.
Set <TT
CLASS="STRUCTFIELD"
>nodeN</TT
> to the index (from zero) of that node in
the node array.
Set <TT
CLASS="STRUCTFIELD"
>levelAdd</TT
> to the increment in
<TT
CLASS="STRUCTFIELD"
>level</TT
> caused by descending through that node,
or leave it as zero if the operator class does not use levels.
Set <TT
CLASS="STRUCTFIELD"
>restDatum</TT
> to equal <TT
CLASS="STRUCTFIELD"
>datum</TT
>
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
<TT
CLASS="STRUCTFIELD"
>leafDatum</TT
> at the next level.
</P
><P
> If a new child node must be added,
set <TT
CLASS="STRUCTFIELD"
>resultType</TT
> to <TT
CLASS="LITERAL"
>spgAddNode</TT
>.
Set <TT
CLASS="STRUCTFIELD"
>nodeLabel</TT
> to the label to be used for the new
node, and set <TT
CLASS="STRUCTFIELD"
>nodeN</TT
> 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 <TT
CLASS="LITERAL"
>spgMatchNode</TT
> result.
</P
><P
> If the new value is inconsistent with the tuple prefix,
set <TT
CLASS="STRUCTFIELD"
>resultType</TT
> to <TT
CLASS="LITERAL"
>spgSplitTuple</TT
>.
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 node that links to the new lower-level inner tuple.
Set <TT
CLASS="STRUCTFIELD"
>prefixHasPrefix</TT
> to indicate whether the new
upper tuple should have a prefix, and if so set
<TT
CLASS="STRUCTFIELD"
>prefixPrefixDatum</TT
> to the prefix value. This new
prefix value must be sufficiently less restrictive than the original
to accept the new value to be indexed, and it should be no longer
than the original prefix.
Set <TT
CLASS="STRUCTFIELD"
>nodeLabel</TT
> to the label to be used for the
node that will point to the new lower-level inner tuple.
Set <TT
CLASS="STRUCTFIELD"
>postfixHasPrefix</TT
> to indicate whether the new
lower-level inner tuple should have a prefix, and if so set
<TT
CLASS="STRUCTFIELD"
>postfixPrefixDatum</TT
> to the prefix value. The
combination of these two prefixes and the additional label 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 will usually result in an <TT
CLASS="LITERAL"
>spgAddNode</TT
> result,
since presumably the node label added in the split step will not
match the new value; so after that, there will be a third call
that finally returns <TT
CLASS="LITERAL"
>spgMatchNode</TT
> and allows the
insertion to descend to the leaf level.
</P
></DD
><DT
><CODE
CLASS="FUNCTION"
>picksplit</CODE
></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 <TT
CLASS="STRUCTNAME"
>spgPickSplitIn</TT
>
C struct, containing input data for the function.
The second argument is a pointer to a <TT
CLASS="STRUCTNAME"
>spgPickSplitOut</TT
>
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>
<TT
CLASS="STRUCTFIELD"
>nTuples</TT
> is the number of leaf tuples provided.
<TT
CLASS="STRUCTFIELD"
>datums</TT
> is an array of their datum values.
<TT
CLASS="STRUCTFIELD"
>level</TT
> is the current level that all the leaf tuples
share, which will become the level of the new inner tuple.
</P
><P
> Set <TT
CLASS="STRUCTFIELD"
>hasPrefix</TT
> to indicate whether the new inner
tuple should have a prefix, and if so set
<TT
CLASS="STRUCTFIELD"
>prefixDatum</TT
> to the prefix value.
Set <TT
CLASS="STRUCTFIELD"
>nNodes</TT
> to indicate the number of nodes that
the new inner tuple will contain, and
set <TT
CLASS="STRUCTFIELD"
>nodeLabels</TT
> to an array of their label values.
(If the nodes do not require labels, set <TT
CLASS="STRUCTFIELD"
>nodeLabels</TT
>
to NULL; see <A
HREF="spgist-implementation.html#SPGIST-NULL-LABELS"
>Section 54.3.2</A
> for details.)
Set <TT
CLASS="STRUCTFIELD"
>mapTuplesToNodes</TT
> to an array that gives the index
(from zero) of the node that each leaf tuple should be assigned to.
Set <TT
CLASS="STRUCTFIELD"
>leafTupleDatums</TT
> to an array of the values to
be stored in the new leaf tuples (these will be the same as the
input <TT
CLASS="STRUCTFIELD"
>datums</TT
> 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
<TT
CLASS="STRUCTFIELD"
>nodeLabels</TT
>, <TT
CLASS="STRUCTFIELD"
>mapTuplesToNodes</TT
> and
<TT
CLASS="STRUCTFIELD"
>leafTupleDatums</TT
> 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
<TT
CLASS="LITERAL"
>allTheSame</TT
> 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
HREF="spgist-implementation.html#SPGIST-ALL-THE-SAME"
>Section 54.3.3</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
<TT
CLASS="STRUCTFIELD"
>longValuesOK</TT
> 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
HREF="spgist-implementation.html#SPGIST-LIMITS"
>Section 54.3.1</A
> for
more information.
</P
></DD
><DT
><CODE
CLASS="FUNCTION"
>inner_consistent</CODE
></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 <TT
CLASS="STRUCTNAME"
>spgInnerConsistentIn</TT
>
C struct, containing input data for the function.
The second argument is a pointer to a <TT
CLASS="STRUCTNAME"
>spgInnerConsistentOut</TT
>
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 */
int nkeys; /* length of array */
Datum reconstructedValue; /* value reconstructed at parent */
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 */
} spgInnerConsistentOut;</PRE
><P>
The array <TT
CLASS="STRUCTFIELD"
>scankeys</TT
>, of length <TT
CLASS="STRUCTFIELD"
>nkeys</TT
>,
describes the index search condition(s). These conditions are
combined with AND — only index entries that satisfy all of
them are interesting. (Note that <TT
CLASS="STRUCTFIELD"
>nkeys</TT
> = 0 implies
that all index entries satisfy the query.) Usually the consistent
function only cares about the <TT
CLASS="STRUCTFIELD"
>sk_strategy</TT
> and
<TT
CLASS="STRUCTFIELD"
>sk_argument</TT
> fields of each array entry, which
respectively give the indexable operator and comparison value.
In particular it is not necessary to check <TT
CLASS="STRUCTFIELD"
>sk_flags</TT
> to
see if the comparison value is NULL, because the SP-GiST core code
will filter out such conditions.
<TT
CLASS="STRUCTFIELD"
>reconstructedValue</TT
> is the value reconstructed for the
parent tuple; it is <TT
CLASS="LITERAL"
>(Datum) 0</TT
> at the root level or if the
<CODE
CLASS="FUNCTION"
>inner_consistent</CODE
> function did not provide a value at the
parent level.
<TT
CLASS="STRUCTFIELD"
>level</TT
> is the current inner tuple's level, starting at
zero for the root level.
<TT
CLASS="STRUCTFIELD"
>returnData</TT
> is <TT
CLASS="LITERAL"
>true</TT
> if reconstructed data is
required for this query; this will only be so if the
<CODE
CLASS="FUNCTION"
>config</CODE
> function asserted <TT
CLASS="STRUCTFIELD"
>canReturnData</TT
>.
<TT
CLASS="STRUCTFIELD"
>allTheSame</TT
> is true if the current inner tuple is
marked <SPAN
CLASS="QUOTE"
>"all-the-same"</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
HREF="spgist-implementation.html#SPGIST-ALL-THE-SAME"
>Section 54.3.3</A
>).
<TT
CLASS="STRUCTFIELD"
>hasPrefix</TT
> is true if the current inner tuple contains
a prefix; if so,
<TT
CLASS="STRUCTFIELD"
>prefixDatum</TT
> is its value.
<TT
CLASS="STRUCTFIELD"
>nNodes</TT
> is the number of child nodes contained in the
inner tuple, and
<TT
CLASS="STRUCTFIELD"
>nodeLabels</TT
> is an array of their label values, or
NULL if the nodes do not have labels.
</P
><P
> <TT
CLASS="STRUCTFIELD"
>nNodes</TT
> must be set to the number of child nodes that
need to be visited by the search, and
<TT
CLASS="STRUCTFIELD"
>nodeNumbers</TT
> must be set to an array of their indexes.
If the operator class keeps track of levels, set
<TT
CLASS="STRUCTFIELD"
>levelAdds</TT
> 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
<TT
CLASS="STRUCTFIELD"
>reconstructedValues</TT
> to an array of the values
reconstructed for each child node to be visited; otherwise, leave
<TT
CLASS="STRUCTFIELD"
>reconstructedValues</TT
> as NULL.
Note that the <CODE
CLASS="FUNCTION"
>inner_consistent</CODE
> function is
responsible for palloc'ing the
<TT
CLASS="STRUCTFIELD"
>nodeNumbers</TT
>, <TT
CLASS="STRUCTFIELD"
>levelAdds</TT
> and
<TT
CLASS="STRUCTFIELD"
>reconstructedValues</TT
> arrays.
</P
></DD
><DT
><CODE
CLASS="FUNCTION"
>leaf_consistent</CODE
></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 <TT
CLASS="STRUCTNAME"
>spgLeafConsistentIn</TT
>
C struct, containing input data for the function.
The second argument is a pointer to a <TT
CLASS="STRUCTNAME"
>spgLeafConsistentOut</TT
>
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 */
int nkeys; /* length of array */
Datum reconstructedValue; /* value reconstructed at parent */
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 */
} spgLeafConsistentOut;</PRE
><P>
The array <TT
CLASS="STRUCTFIELD"
>scankeys</TT
>, of length <TT
CLASS="STRUCTFIELD"
>nkeys</TT
>,
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 <TT
CLASS="STRUCTFIELD"
>nkeys</TT
> = 0 implies
that all index entries satisfy the query.) Usually the consistent
function only cares about the <TT
CLASS="STRUCTFIELD"
>sk_strategy</TT
> and
<TT
CLASS="STRUCTFIELD"
>sk_argument</TT
> fields of each array entry, which
respectively give the indexable operator and comparison value.
In particular it is not necessary to check <TT
CLASS="STRUCTFIELD"
>sk_flags</TT
> to
see if the comparison value is NULL, because the SP-GiST core code
will filter out such conditions.
<TT
CLASS="STRUCTFIELD"
>reconstructedValue</TT
> is the value reconstructed for the
parent tuple; it is <TT
CLASS="LITERAL"
>(Datum) 0</TT
> at the root level or if the
<CODE
CLASS="FUNCTION"
>inner_consistent</CODE
> function did not provide a value at the
parent level.
<TT
CLASS="STRUCTFIELD"
>level</TT
> is the current leaf tuple's level, starting at
zero for the root level.
<TT
CLASS="STRUCTFIELD"
>returnData</TT
> is <TT
CLASS="LITERAL"
>true</TT
> if reconstructed data is
required for this query; this will only be so if the
<CODE
CLASS="FUNCTION"
>config</CODE
> function asserted <TT
CLASS="STRUCTFIELD"
>canReturnData</TT
>.
<TT
CLASS="STRUCTFIELD"
>leafDatum</TT
> is the key value stored in the current
leaf tuple.
</P
><P
> The function must return <TT
CLASS="LITERAL"
>true</TT
> if the leaf tuple matches the
query, or <TT
CLASS="LITERAL"
>false</TT
> if not. In the <TT
CLASS="LITERAL"
>true</TT
> case,
if <TT
CLASS="STRUCTFIELD"
>returnData</TT
> is <TT
CLASS="LITERAL"
>true</TT
> then
<TT
CLASS="STRUCTFIELD"
>leafValue</TT
> must be set to the value originally supplied
to be indexed for this leaf tuple. Also,
<TT
CLASS="STRUCTFIELD"
>recheck</TT
> may be set to <TT
CLASS="LITERAL"
>true</TT
> if the match
is uncertain and so the operator(s) must be re-applied to the actual
heap tuple to verify the match.
</P
></DD
></DL
></DIV
><P
> All the SP-GiST support methods are normally called in a short-lived
memory context; that is, <TT
CLASS="VARNAME"
>CurrentMemoryContext</TT
> 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
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