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diff --git a/doc/src/sgml/html/brin-extensibility.html b/doc/src/sgml/html/brin-extensibility.html new file mode 100644 index 0000000..95c7166 --- /dev/null +++ b/doc/src/sgml/html/brin-extensibility.html @@ -0,0 +1,137 @@ +<?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>67.3. 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="brin-builtin-opclasses.html" title="67.2. Built-in Operator Classes" /><link rel="next" href="hash-index.html" title="Chapter 68. Hash Indexes" /></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">67.3. Extensibility</th></tr><tr><td width="10%" align="left"><a accesskey="p" href="brin-builtin-opclasses.html" title="67.2. Built-in Operator Classes">Prev</a> </td><td width="10%" align="left"><a accesskey="u" href="brin.html" title="Chapter 67. BRIN Indexes">Up</a></td><th width="60%" align="center">Chapter 67. BRIN 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="hash-index.html" title="Chapter 68. Hash Indexes">Next</a></td></tr></table><hr></hr></div><div class="sect1" id="BRIN-EXTENSIBILITY"><div class="titlepage"><div><div><h2 class="title" style="clear: both">67.3. Extensibility</h2></div></div></div><p> + The <acronym class="acronym">BRIN</acronym> interface has a high level of abstraction, + requiring the access method implementer only to implement the semantics + of the data type being accessed. The <acronym class="acronym">BRIN</acronym> layer + itself takes care of concurrency, logging and searching the index structure. + </p><p> + All it takes to get a <acronym class="acronym">BRIN</acronym> access method working is to + implement a few user-defined methods, which define the behavior of + summary values stored in the index and the way they interact with + scan keys. + In short, <acronym class="acronym">BRIN</acronym> combines + extensibility with generality, code reuse, and a clean interface. + </p><p> + There are four methods that an operator class for <acronym class="acronym">BRIN</acronym> + must provide: + + </p><div class="variablelist"><dl class="variablelist"><dt><span class="term"><code class="function">BrinOpcInfo *opcInfo(Oid type_oid)</code></span></dt><dd><p> + Returns internal information about the indexed columns' summary data. + The return value must point to a palloc'd <code class="structname">BrinOpcInfo</code>, + which has this definition: +</p><pre class="programlisting"> +typedef struct BrinOpcInfo +{ + /* Number of columns stored in an index column of this opclass */ + uint16 oi_nstored; + + /* Opaque pointer for the opclass' private use */ + void *oi_opaque; + + /* Type cache entries of the stored columns */ + TypeCacheEntry *oi_typcache[FLEXIBLE_ARRAY_MEMBER]; +} BrinOpcInfo; +</pre><p> + <code class="structname">BrinOpcInfo</code>.<code class="structfield">oi_opaque</code> can be used by the + operator class routines to pass information between support functions + during an index scan. + </p></dd><dt><span class="term"><code class="function">bool consistent(BrinDesc *bdesc, BrinValues *column, + ScanKey key)</code></span></dt><dd><p> + Returns whether the ScanKey is consistent with the given indexed + values for a range. + The attribute number to use is passed as part of the scan key. + </p></dd><dt><span class="term"><code class="function">bool addValue(BrinDesc *bdesc, BrinValues *column, + Datum newval, bool isnull)</code></span></dt><dd><p> + Given an index tuple and an indexed value, modifies the indicated + attribute of the tuple so that it additionally represents the new value. + If any modification was done to the tuple, <code class="literal">true</code> is + returned. + </p></dd><dt><span class="term"><code class="function">bool unionTuples(BrinDesc *bdesc, BrinValues *a, + BrinValues *b)</code></span></dt><dd><p> + Consolidates two index tuples. Given two index tuples, modifies the + indicated attribute of the first of them so that it represents both tuples. + The second tuple is not modified. + </p></dd></dl></div><p> + + An operator class for <acronym class="acronym">BRIN</acronym> can optionally specify the + following method: + + </p><div class="variablelist"><dl class="variablelist"><dt><span class="term"><code class="function">void options(local_relopts *relopts)</code></span></dt><dd><p> + Defines a set of user-visible parameters that control operator class + behavior. + </p><p> + The <code class="function">options</code> 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 both key extraction of indexed values and representation of the + key in <acronym class="acronym">BRIN</acronym> are flexible, they may depend on + user-specified parameters. + </p></dd></dl></div><p> + + The core distribution includes support for two types of operator classes: + minmax and inclusion. Operator class definitions using them are shipped for + in-core data types as appropriate. Additional operator classes can be + defined by the user for other data types using equivalent definitions, + without having to write any source code; appropriate catalog entries being + declared is enough. Note that assumptions about the semantics of operator + strategies are embedded in the support functions' source code. + </p><p> + Operator classes that implement completely different semantics are also + possible, provided implementations of the four main support functions + described above are written. Note that backwards compatibility across major + releases is not guaranteed: for example, additional support functions might + be required in later releases. + </p><p> + To write an operator class for a data type that implements a totally + ordered set, it is possible to use the minmax support functions + alongside the corresponding operators, as shown in + <a class="xref" href="brin-extensibility.html#BRIN-EXTENSIBILITY-MINMAX-TABLE" title="Table 67.2. Function and Support Numbers for Minmax Operator Classes">Table 67.2</a>. + All operator class members (functions and operators) are mandatory. + </p><div class="table" id="BRIN-EXTENSIBILITY-MINMAX-TABLE"><p class="title"><strong>Table 67.2. Function and Support Numbers for Minmax Operator Classes</strong></p><div class="table-contents"><table class="table" summary="Function and Support Numbers for Minmax Operator Classes" border="1"><colgroup><col class="col1" /><col class="col2" /></colgroup><thead><tr><th>Operator class member</th><th>Object</th></tr></thead><tbody><tr><td>Support Function 1</td><td>internal function <code class="function">brin_minmax_opcinfo()</code></td></tr><tr><td>Support Function 2</td><td>internal function <code class="function">brin_minmax_add_value()</code></td></tr><tr><td>Support Function 3</td><td>internal function <code class="function">brin_minmax_consistent()</code></td></tr><tr><td>Support Function 4</td><td>internal function <code class="function">brin_minmax_union()</code></td></tr><tr><td>Operator Strategy 1</td><td>operator less-than</td></tr><tr><td>Operator Strategy 2</td><td>operator less-than-or-equal-to</td></tr><tr><td>Operator Strategy 3</td><td>operator equal-to</td></tr><tr><td>Operator Strategy 4</td><td>operator greater-than-or-equal-to</td></tr><tr><td>Operator Strategy 5</td><td>operator greater-than</td></tr></tbody></table></div></div><br class="table-break" /><p> + To write an operator class for a complex data type which has values + included within another type, it's possible to use the inclusion support + functions alongside the corresponding operators, as shown + in <a class="xref" href="brin-extensibility.html#BRIN-EXTENSIBILITY-INCLUSION-TABLE" title="Table 67.3. Function and Support Numbers for Inclusion Operator Classes">Table 67.3</a>. It requires + only a single additional function, which can be written in any language. + More functions can be defined for additional functionality. All operators + are optional. Some operators require other operators, as shown as + dependencies on the table. + </p><div class="table" id="BRIN-EXTENSIBILITY-INCLUSION-TABLE"><p class="title"><strong>Table 67.3. Function and Support Numbers for Inclusion Operator Classes</strong></p><div class="table-contents"><table class="table" summary="Function and Support Numbers for Inclusion Operator Classes" border="1"><colgroup><col class="col1" /><col class="col2" /><col class="col3" /></colgroup><thead><tr><th>Operator class member</th><th>Object</th><th>Dependency</th></tr></thead><tbody><tr><td>Support Function 1</td><td>internal function <code class="function">brin_inclusion_opcinfo()</code></td><td> </td></tr><tr><td>Support Function 2</td><td>internal function <code class="function">brin_inclusion_add_value()</code></td><td> </td></tr><tr><td>Support Function 3</td><td>internal function <code class="function">brin_inclusion_consistent()</code></td><td> </td></tr><tr><td>Support Function 4</td><td>internal function <code class="function">brin_inclusion_union()</code></td><td> </td></tr><tr><td>Support Function 11</td><td>function to merge two elements</td><td> </td></tr><tr><td>Support Function 12</td><td>optional function to check whether two elements are mergeable</td><td> </td></tr><tr><td>Support Function 13</td><td>optional function to check if an element is contained within another</td><td> </td></tr><tr><td>Support Function 14</td><td>optional function to check whether an element is empty</td><td> </td></tr><tr><td>Operator Strategy 1</td><td>operator left-of</td><td>Operator Strategy 4</td></tr><tr><td>Operator Strategy 2</td><td>operator does-not-extend-to-the-right-of</td><td>Operator Strategy 5</td></tr><tr><td>Operator Strategy 3</td><td>operator overlaps</td><td> </td></tr><tr><td>Operator Strategy 4</td><td>operator does-not-extend-to-the-left-of</td><td>Operator Strategy 1</td></tr><tr><td>Operator Strategy 5</td><td>operator right-of</td><td>Operator Strategy 2</td></tr><tr><td>Operator Strategy 6, 18</td><td>operator same-as-or-equal-to</td><td>Operator Strategy 7</td></tr><tr><td>Operator Strategy 7, 13, 16, 24, 25</td><td>operator contains-or-equal-to</td><td> </td></tr><tr><td>Operator Strategy 8, 14, 26, 27</td><td>operator is-contained-by-or-equal-to</td><td>Operator Strategy 3</td></tr><tr><td>Operator Strategy 9</td><td>operator does-not-extend-above</td><td>Operator Strategy 11</td></tr><tr><td>Operator Strategy 10</td><td>operator is-below</td><td>Operator Strategy 12</td></tr><tr><td>Operator Strategy 11</td><td>operator is-above</td><td>Operator Strategy 9</td></tr><tr><td>Operator Strategy 12</td><td>operator does-not-extend-below</td><td>Operator Strategy 10</td></tr><tr><td>Operator Strategy 20</td><td>operator less-than</td><td>Operator Strategy 5</td></tr><tr><td>Operator Strategy 21</td><td>operator less-than-or-equal-to</td><td>Operator Strategy 5</td></tr><tr><td>Operator Strategy 22</td><td>operator greater-than</td><td>Operator Strategy 1</td></tr><tr><td>Operator Strategy 23</td><td>operator greater-than-or-equal-to</td><td>Operator Strategy 1</td></tr></tbody></table></div></div><br class="table-break" /><p> + Support function numbers 1 through 10 are reserved for the BRIN internal + functions, so the SQL level functions start with number 11. Support + function number 11 is the main function required to build the index. + It should accept two arguments with the same data type as the operator class, + and return the union of them. The inclusion operator class can store union + values with different data types if it is defined with the + <code class="literal">STORAGE</code> parameter. The return value of the union + function should match the <code class="literal">STORAGE</code> data type. + </p><p> + Support function numbers 12 and 14 are provided to support + irregularities of built-in data types. Function number 12 + is used to support network addresses from different families which + are not mergeable. Function number 14 is used to support + empty ranges. Function number 13 is an optional but + recommended one, which allows the new value to be checked before + it is passed to the union function. As the BRIN framework can shortcut + some operations when the union is not changed, using this + function can improve index performance. + </p><p> + Both minmax and inclusion operator classes support cross-data-type + operators, though with these the dependencies become more complicated. + The minmax operator class requires a full set of operators to be + defined with both arguments having the same data type. It allows + additional data types to be supported by defining extra sets + of operators. Inclusion operator class operator strategies are dependent + on another operator strategy as shown in + <a class="xref" href="brin-extensibility.html#BRIN-EXTENSIBILITY-INCLUSION-TABLE" title="Table 67.3. Function and Support Numbers for Inclusion Operator Classes">Table 67.3</a>, or the same + operator strategy as themselves. They require the dependency + operator to be defined with the <code class="literal">STORAGE</code> data type as the + left-hand-side argument and the other supported data type to be the + right-hand-side argument of the supported operator. See + <code class="literal">float4_minmax_ops</code> as an example of minmax, and + <code class="literal">box_inclusion_ops</code> as an example of inclusion. + </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="brin-builtin-opclasses.html" title="67.2. Built-in Operator Classes">Prev</a> </td><td width="20%" align="center"><a accesskey="u" href="brin.html" title="Chapter 67. BRIN Indexes">Up</a></td><td width="40%" align="right"> <a accesskey="n" href="hash-index.html" title="Chapter 68. Hash Indexes">Next</a></td></tr><tr><td width="40%" align="left" valign="top">67.2. 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