<field name="id" type="string" indexed="true" stored="true" required="true" multiValued="false" />
常用的公共属性有：
name：标识。
type：fieldType定义的类型。
indexed=true|false：是否被用来建立索引（关系到搜索和排序）
stored=true|false：是否储存
compressed=true|false，是否使用gzip压缩（只有TextField和StrField可以压缩）
compressThreshold=压缩阀值
multiValued=true|false 是否包含多个值,即一个名字可以被多个document所用。
omitNorms=true|false这是个高级选项。设置为true，省略与这一field相关的规范（这将禁用长度规范化和索引时间权重( index-time boosting for the field)，并节省一些内存）。仅仅用在全文本field。
omitNorms在建立索引时会存储相关的影响boost打分的长度因子，因此对于不需要打分排序考虑的，omitNorm设置成true。
termVectors=false|true 如果设置为true，则包含了所有的term vector 信息。通常用的属性有：
termPositions=”true”：存储 term vector中的地址信息，会消耗存储开销。
termOffsets：存储 term vector 的偏移量，会消耗存储开销。
更多有关信息请参考：http://wiki.apache.org/solr/TermVectorComponent
omitTermFreqAndPositions=true|false 如果设置，省略掉freq和term vector中的地址信息
omitPositions=true|false如果设置，省略掉term vector中的地址信息
default：如果没有属性需要修改，就可以用这个标识下。
英文原文：
Common options that fields can have are...
default
The default value for this field if none is provided while adding documents
indexed=true|false
True if this field should be "indexed". If (and only if) a field is indexed, then it is searchable, sortable, and facetable.
stored=true|false
True if the value of the field should be retrievable during a search, or if you're using highlighting or MoreLikeThis.
compressed=true|false
True if this field should be stored using gzip compression. (This will only apply if the field type is compressible; among the standard field types, only TextField and StrField are.)
compressThreshold=<integer>
multiValued=true|false
True if this field may contain multiple values per document, i.e. if it can appear multiple times in a document
omitNorms=true|false
This is arguably an advanced option.
Set to true to omit the norms associated with this field (this disables length normalization and index-time boosting for the field, and saves some memory). Only full-text fields or fields that need an index-time boost need norms.
termVectors=false|true <?> Solr 1.1
If set, include full term vector info.
If enabled, often also used with termPositions="true" and termOffsets="true".
To use interactively, requires TermVectorComponent
Corresponds to TV button in Luke, and V field attribute.
omitTermFreqAndPositions=true|false <!> Solr1.4
If set, omit term freq, positions and payloads from postings for this field. This can be a performance boost for fields that don't require that information and reduces storage space required for the index. Queries that rely on position that are issued on a field with this option fail with an exception. Prior to <!> Solr4.0 the queries would silently fail to find documents.
omitPositions=true|false <!> Solr3.4
If set, omits positions, but keeps term frequencies