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Reviewed-by: Goncharov, Artem <artem.goncharov@t-systems.com> Co-authored-by: gtema <artem.goncharov@gmail.com> Co-committed-by: gtema <artem.goncharov@gmail.com>
58 lines
5.8 KiB
HTML
58 lines
5.8 KiB
HTML
<a name="css_04_0003"></a><a name="css_04_0003"></a>
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<h1 class="topictitle1">Basic Concepts</h1>
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<div id="body8662426"><div class="section" id="css_04_0003__en-us_topic_0103614115_section1830421944212"><h4 class="sectiontitle">Cluster</h4><p id="css_04_0003__en-us_topic_0103614115_p191791321134214"><span id="css_04_0003__text945015352611">CSS</span> provides functions on a per cluster basis. A cluster represents an independent search service that contains multiple nodes.</p>
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</div>
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<div class="section" id="css_04_0003__en-us_topic_0103614115_section19166022134218"><h4 class="sectiontitle">Index</h4><p id="css_04_0003__en-us_topic_0103614115_p1388689508">Index is similar to "database" in the relational database (RDB) and stores Elasticsearch data. It refers to a logical space that consists of one or more shards.</p>
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<div class="tablenoborder"><table cellpadding="4" cellspacing="0" summary="" id="css_04_0003__en-us_topic_0103614115_table748644118216" frame="border" border="1" rules="all"><caption><b>Table 1 </b>Mapping between Elasticsearch and RDB</caption><tbody><tr id="css_04_0003__en-us_topic_0103614115_row1448718416214"><th class="firstcol" valign="top" width="22.772277227722775%" id="mcps1.3.2.3.2.7.1.1"><p id="css_04_0003__en-us_topic_0103614115_p84877416219">Elasticsearch</p>
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</th>
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<td class="cellrowborder" valign="top" width="14.85148514851485%" headers="mcps1.3.2.3.2.7.1.1 "><p id="css_04_0003__en-us_topic_0103614115_p2048764117216">Index</p>
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</td>
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<td class="cellrowborder" valign="top" width="16.831683168316832%" headers="mcps1.3.2.3.2.7.1.1 "><p id="css_04_0003__en-us_topic_0103614115_p15487184192119">Type</p>
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</td>
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<td class="cellrowborder" valign="top" width="16.831683168316832%" headers="mcps1.3.2.3.2.7.1.1 "><p id="css_04_0003__en-us_topic_0103614115_p6487184115215">Document</p>
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</td>
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<td class="cellrowborder" valign="top" width="12.871287128712872%" headers="mcps1.3.2.3.2.7.1.1 "><p id="css_04_0003__en-us_topic_0103614115_p1948719411216">Field</p>
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</td>
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<td class="cellrowborder" valign="top" width="15.841584158415841%" headers="mcps1.3.2.3.2.7.1.1 "><p id="css_04_0003__en-us_topic_0103614115_p5180916821">Mapping</p>
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</td>
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</tr>
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<tr id="css_04_0003__en-us_topic_0103614115_row109591755537"><th class="firstcol" valign="top" width="22.772277227722775%" id="mcps1.3.2.3.2.7.2.1"><p id="css_04_0003__en-us_topic_0103614115_p7874502418">RDB</p>
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</th>
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<td class="cellrowborder" valign="top" width="14.85148514851485%" headers="mcps1.3.2.3.2.7.2.1 "><p id="css_04_0003__en-us_topic_0103614115_p108747011416">Database</p>
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</td>
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<td class="cellrowborder" valign="top" width="16.831683168316832%" headers="mcps1.3.2.3.2.7.2.1 "><p id="css_04_0003__en-us_topic_0103614115_p198746014410">Table</p>
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</td>
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<td class="cellrowborder" valign="top" width="16.831683168316832%" headers="mcps1.3.2.3.2.7.2.1 "><p id="css_04_0003__en-us_topic_0103614115_p128741601746">Row</p>
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</td>
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<td class="cellrowborder" valign="top" width="12.871287128712872%" headers="mcps1.3.2.3.2.7.2.1 "><p id="css_04_0003__en-us_topic_0103614115_p11874120441">Column</p>
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</td>
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<td class="cellrowborder" valign="top" width="15.841584158415841%" headers="mcps1.3.2.3.2.7.2.1 "><p id="css_04_0003__en-us_topic_0103614115_p0874401749">Schema</p>
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</td>
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</tr>
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</tbody>
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</table>
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</div>
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</div>
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<div class="section" id="css_04_0003__en-us_topic_0103614115_section78422819503"><h4 class="sectiontitle">Shard</h4><p id="css_04_0003__en-us_topic_0103614115_p1359584214432">An index can potentially store a large amount of data that exceeds the hardware limits of a single node. To solve this problem, Elasticsearch subdivides your index into multiple pieces called shards. When you create an index, you can simply define the number of shards that you want. Each shard is in itself a fully-functional and independent "index" that can be hosted on any node in the cluster.</p>
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<p id="css_04_0003__en-us_topic_0103614115_p10203313115011">You need to specify the number of shards before creating an index and cannot change the number of shards after the index is created.</p>
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</div>
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<div class="section" id="css_04_0003__en-us_topic_0103614115_section1728813145500"><h4 class="sectiontitle">Replica</h4><p id="css_04_0003__en-us_topic_0103614115_p824420163507">A replica is a copy of the actual storage index in a shard. It can be understood as a backup of the shard. Replicas help prevent single point of failures (SPOFs). You can increase or decrease the number of replicas based on your service requirements.</p>
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</div>
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<div class="section" id="css_04_0003__en-us_topic_0103614115_section95801224500"><h4 class="sectiontitle">Document</h4><p id="css_04_0003__en-us_topic_0103614115_p16549143318507">An entity for Elasticsearch storage. Equivalent to a row in the RDB, the document is the basic unit that can be indexed.</p>
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</div>
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<div class="section" id="css_04_0003__en-us_topic_0103614115_section05836341509"><h4 class="sectiontitle">Type</h4><p id="css_04_0003__en-us_topic_0103614115_p1919417361508">Similar to a table in the RDB, type is used to distinguish between different data. One index can contain multiple document types. A document must be indexed to a document type inside an index.</p>
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</div>
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<div class="section" id="css_04_0003__en-us_topic_0103614115_section6795201915110"><h4 class="sectiontitle">Mapping</h4><p id="css_04_0003__en-us_topic_0103614115_p186618368513">A mapping is used to restrict the type of a field and is automatically created based on data. It is similar to a schema in the database.</p>
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</div>
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<div class="section" id="css_04_0003__en-us_topic_0103614115_section155732145251"><h4 class="sectiontitle">Field</h4><p id="css_04_0003__en-us_topic_0103614115_p1962702532513">Minimum unit of a document. A field is similar to a column in a database.</p>
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</div>
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</div>
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<div>
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<div class="familylinks">
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<div class="parentlink"><strong>Parent topic:</strong> <a href="css_01_0001.html">Overview</a></div>
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</div>
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</div>
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