为什么要有索引
gremlin 其实是一个逐级过滤的运行机制，比如下面的一个简单的gremlin查询语句：
g.V().hasLabel("label").has("prop","value")
运行原理就是：
- 找出所有的顶点V
- 然后过滤出label为label的数据
- 然后过滤出prop=value的数据
当数据量很大时，这个代价非常大，因此需要做查询优化。
hugegraph 的优化方案是，HugeGraphStepStrategy 中将has条件提取出来，然后走索引优化，减少读取的数据量。
TraversalUtil.extractHasContainer:
public static void extractHasContainer(HugeGraphStep<?, ?> newStep,
Traversal.Admin<?, ?> traversal) {
Step<?, ?> step = newStep;
do {
step = step.getNextStep();
if (step instanceof HasStep) {
HasContainerHolder holder = (HasContainerHolder) step;
for (HasContainer has : holder.getHasContainers()) {
if (!GraphStep.processHasContainerIds(newStep, has)) {
newStep.addHasContainer(has);
}
}
TraversalHelper.copyLabels(step, step.getPreviousStep(), false);
traversal.removeStep(step);
}
} while (step instanceof HasStep || step instanceof NoOpBarrierStep);
}
hugegraph索引介绍
hugegraph 通过IndexLabel 来定义索引类型，描述索引的约束信息。
- indexType: 建立的索引类型，目前支持五种，即 Secondary、Range、Search、Shard 和 Unique。
-
Secondary 支持精确匹配的二级索引，允许建立联合索引，联合索引支持索引前缀搜索
-
单个属性，支持相等查询，比如：person顶点的city属性的二级索引，可以用
g.V().has("city", "北京")查询"city属性值是北京"的全部顶点 -
联合索引，支持前缀查询和相等查询，比如：person顶点的city和street属性的联合索引，可以用
g.V().has ("city", "北京").has('street', '中关村街道')查询"city属性值是北京且street属性值是中关村"的全部顶点，或者g.V() .has("city", "北京")查询"city属性值是北京"的全部顶点secondary index的查询都是基于"是"或者"相等"的查询条件，不支持"部分匹配"
-
-
Range 支持数值类型的范围查询
- 必须是单个数字或者日期属性，比如：person顶点的age属性的范围索引，可以用
g.V().has("age", P.gt(18))查询"age属性值大于18"的顶点。除了P.gt()以外，还支持P.gte(),P.lte(),P.lt(),P.eq(),P.between(),P.inside()和P.outside()等
- 必须是单个数字或者日期属性，比如：person顶点的age属性的范围索引，可以用
-
Search 支持全文检索的索引
-
必须是单个文本属性，比如：person顶点的address属性的全文索引，可以用
g.V().has("address", Text .contains('大厦')查询"address属性中包含大厦"的全部顶点search index的查询是基于"是"或者"包含"的查询条件
-
-
Shard 支持前缀匹配 + 数字范围查询的索引
-
N个属性的分片索引，支持前缀相等情况下的范围查询，比如：person顶点的city和age属性的分片索引，可以用
g.V().has ("city", "北京").has("age", P.between(18, 30))查询"city属性是北京且年龄大于等于18小于30"的全部顶点 -
shard index N个属性全是文本属性时，等价于secondary index
-
shard index只有单个数字或者日期属性时，等价于range index
shard index可以有任意数字或者日期属性，但是查询时最多只能提供一个范围查找条件，且该范围查找条件的属性的前缀属性都是相等查询条件
-
-
Unique 支持属性值唯一性约束，即可以限定属性的值不重复，允许联合索引，但不支持查询
- 单个或者多个属性的唯一性索引，不可用来查询，只可对属性的值进行限定，当出现重复值时将报错
-
摘录自 https://hugegraph.github.io/hugegraph-doc/clients/hugegraph-client.html
Secondary 和 Range是最常用的索引。
索引存储原理
我们通过源代码来分析索引存储过程。 核心代码在GraphIndexTransaction.updateIndex函数里：
/**
* Update index(user properties) of vertex or edge
* @param ilId the id of index label
* @param element the properties owner
* @param removed remove or add index
*/
protected void updateIndex(Id ilId, HugeElement element, boolean removed) {
SchemaTransaction schema = this.params().schemaTransaction();
IndexLabel indexLabel = schema.getIndexLabel(ilId);
E.checkArgument(indexLabel != null,
"Not exist index label with id '%s'", ilId);
// Collect property values of index fields
List<Object> allPropValues = new ArrayList<>();
int fieldsNum = indexLabel.indexFields().size();
int firstNullField = fieldsNum;
for (Id fieldId : indexLabel.indexFields()) {
HugeProperty<Object> property = element.getProperty(fieldId);
if (property == null) {
E.checkState(hasNullableProp(element, fieldId),
"Non-null property '%s' is null for '%s'",
this.graph().propertyKey(fieldId) , element);
if (firstNullField == fieldsNum) {
firstNullField = allPropValues.size();
}
allPropValues.add(INDEX_SYM_NULL);
} else {
E.checkArgument(!INDEX_SYM_NULL.equals(property.value()),
"Illegal value of index property: '%s'",
INDEX_SYM_NULL);
allPropValues.add(property.value());
}
}
if (firstNullField == 0 && !indexLabel.indexType().isUnique()) {
// The property value of first index field is null
return;
}
// Not build index for record with nullable field (except unique index)
List<Object> propValues = allPropValues.subList(0, firstNullField);
// Expired time
long expiredTime = element.expiredTime();
// Update index for each index type
switch (indexLabel.indexType()) {
case RANGE_INT:
case RANGE_FLOAT:
case RANGE_LONG:
case RANGE_DOUBLE:
E.checkState(propValues.size() == 1,
"Expect only one property in range index");
Object value = NumericUtil.convertToNumber(propValues.get(0));
this.updateIndex(indexLabel, value, element.id(),
expiredTime, removed);
break;
case SEARCH:
E.checkState(propValues.size() == 1,
"Expect only one property in search index");
value = propValues.get(0);
Set<String> words = this.segmentWords(value.toString());
for (String word : words) {
this.updateIndex(indexLabel, word, element.id(),
expiredTime, removed);
}
break;
case SECONDARY:
// Secondary index maybe include multi prefix index
for (int i = 0, n = propValues.size(); i < n; i++) {
List<Object> prefixValues = propValues.subList(0, i + 1);
// prefixValues is list or set , should create index for
// each item
if(prefixValues.get(0) instanceof Collection) {
for (Object propValue :
(Collection<Object>) prefixValues.get(0)) {
value = escapeIndexValueIfNeeded(propValue.toString());
this.updateIndex(indexLabel, value, element.id(),
expiredTime, removed);
}
}else {
value = ConditionQuery.concatValues(prefixValues);
value = escapeIndexValueIfNeeded((String) value);
this.updateIndex(indexLabel, value, element.id(),
expiredTime, removed);
}
}
break;
case SHARD:
value = ConditionQuery.concatValues(propValues);
value = escapeIndexValueIfNeeded((String) value);
this.updateIndex(indexLabel, value, element.id(),
expiredTime, removed);
break;
case UNIQUE:
value = ConditionQuery.concatValues(allPropValues);
assert !value.equals("");
Id id = element.id();
// TODO: add lock for updating unique index
if (!removed && this.existUniqueValue(indexLabel, value, id)) {
throw new IllegalArgumentException(String.format(
"Unique constraint %s conflict is found for %s",
indexLabel, element));
}
this.updateIndex(indexLabel, value, element.id(),
expiredTime, removed);
break;
default:
throw new AssertionError(String.format(
"Unknown index type '%s'", indexLabel.indexType()));
}
}
- 参数是索引id，数据HugeElement
- 先schema.getIndexLabel(ilId)，根据索引id获取到indexlabel
- 然后根据indexlabel中的字段获取element中的属性值
- 然后根据switch索引类型，来处理索引。
当用户的查询语义是：某属性值大于、小于、大于等于、小于等于、等于某个界限，或者属性值属于某个区间时，适合使用范围索引。比如：“年龄”、“价格”、“得分”等取值比较连续的属性。
范围索引处理方式如下：
- 先检查属性值个数是否为1，范围索引不支持组合索引。
- 然后updateIndex，保存索引
E.checkState(propValues.size() == 1,
"Expect only one property in range index");
Object value = NumericUtil.convertToNumber(propValues.get(0));
this.updateIndex(indexLabel, value, element.id(),
expiredTime, removed);
updateIndex 代码：
private void updateIndex(IndexLabel indexLabel, Object propValue,
Id elementId, long expiredTime, boolean removed) {
HugeIndex index = new HugeIndex(this.graph(), indexLabel);
index.fieldValues(propValue);
index.elementIds(elementId, expiredTime);
if (removed) {
this.doEliminate(this.serializer.writeIndex(index));
} else {
this.doAppend(this.serializer.writeIndex(index));
}
}
- 构造索引，根据removed来决定是append还是删除。
- 通过GraphSerializer序列化索引
这里我们来探索Serializer是如何做的，比如Binary:
Id id = index.id();
HugeType type = index.type();
byte[] value = null;
if (!type.isNumericIndex() && indexIdLengthExceedLimit(id)) {
id = index.hashId();
// Save field-values as column value if the key is a hash string
value = StringEncoding.encode(index.fieldValues().toString());
}
entry = newBackendEntry(type, id);
entry.column(this.formatIndexName(index), value);
entry.subId(index.elementId());
if (index.hasTtl()) {
entry.ttl(index.ttl());
}
- 生成一个BackendEntry，id为索引id
- column name 通过formatIndexName生成， value 一般为null
- subId为elementid
索引的id：
public static Id formatIndexId(HugeType type, Id indexLabelId,
Object fieldValues) {
if (type.isStringIndex()) {
String value = "";
if (fieldValues instanceof Id) {
value = IdGenerator.asStoredString((Id) fieldValues);
} else if (fieldValues != null) {
value = fieldValues.toString();
}
/*
* Modify order between index label and field-values to put the
* index label in front(hugegraph-1317)
*/
String strIndexLabelId = IdGenerator.asStoredString(indexLabelId);
return SplicingIdGenerator.splicing(strIndexLabelId, value);
} else {
assert type.isRangeIndex();
int length = type.isRange4Index() ? 4 : 8;
BytesBuffer buffer = BytesBuffer.allocate(4 + length);
buffer.writeInt(SchemaElement.schemaId(indexLabelId));
if (fieldValues != null) {
E.checkState(fieldValues instanceof Number,
"Field value of range index must be number:" +
" %s", fieldValues.getClass().getSimpleName());
byte[] bytes = number2bytes((Number) fieldValues);
buffer.write(bytes);
}
return buffer.asId();
}
}
- 如果是rangeindex，id为 SchemaElement.schemaId(indexLabelId) + fieldValues
- 如果是字符串索引，id为 indexLabelId:fieldValues 拼接为字符串 （SplicingIdGenerator.splicing(）
protected byte[] formatIndexName(HugeIndex index) {
BytesBuffer buffer;
Id elemId = index.elementId();
if (!this.indexWithIdPrefix) {
int idLen = 1 + elemId.length();
buffer = BytesBuffer.allocate(idLen);
} else {
Id indexId = index.id();
HugeType type = index.type();
if (!type.isNumericIndex() && indexIdLengthExceedLimit(indexId)) {
indexId = index.hashId();
}
int idLen = 1 + elemId.length() + 1 + indexId.length();
buffer = BytesBuffer.allocate(idLen);
// Write index-id
buffer.writeIndexId(indexId, type);
}
// Write element-id
buffer.writeId(elemId);
// Write expired time if needed
if (index.hasTtl()) {
buffer.writeVLong(index.expiredTime());
}
return buffer.bytes();
}
formatIndexName 决定了column name：
- 先写入indexId，也就是上面（formatIndexId）生成的index id
- 再写入elemId
最后写入存储后端时，
@Override
public void insert(Session session, BackendEntry entry) {
assert !entry.columns().isEmpty();
for (BackendColumn col : entry.columns()) {
assert entry.belongToMe(col) : entry;
session.put(this.table(), col.name, col.value);
}
}
对于range 索引，key的前缀是Int的indexLabelId，中间是索引值的bytes，后缀是elementid，因此range索引天然是有序的。
存储结构：
index_label_id | field_values | element_ids
对于二级索引，也是：
indexLabelId | fieldValues | element_ids
field_values: 属性的值，可以是单个属性，也可以是多个属性拼接而成index_label_id: 索引标签的Idelement_ids: 顶点或边的Id
索引查询过程分析
查询要从GraphTransaction的query开始分析，针对ConditionQuery条件查询，会调用optimizeQueries优化查询。
public QueryResults<BackendEntry> query(Query query) {
if (!(query instanceof ConditionQuery)) {
LOG.debug("Query{final:{}}", query);
return super.query(query);
}
QueryList<BackendEntry> queries = this.optimizeQueries(query,
super::query);
LOG.debug("{}", queries);
return queries.empty() ? QueryResults.empty() :
queries.fetch(this.pageSize);
}
optimizeQueries 会将condtion query flatten展开（比如in查询，展开成多个查询），然后针对每个cq做查询。
针对每个cq，会调用indexQuery走索引查询。
protected <R> QueryList<R> optimizeQueries(Query query,
QueryResults.Fetcher<R> fetcher) {
QueryList<R> queries = new QueryList<>(query, fetcher);
for (ConditionQuery cq: ConditionQueryFlatten.flatten(
(ConditionQuery) query)) {
// Optimize by sysprop
Query q = this.optimizeQuery(cq);
/*
* NOTE: There are two possibilities for this query:
* 1.sysprop-query, which would not be empty.
* 2.index-query result(ids after optimization), which may be empty.
*/
if (q == null) {
queries.add(this.indexQuery(cq), this.batchSize);
} else if (!q.empty()) {
queries.add(q);
}
}
return queries;
}
索引查询，核心代码在 GraphIndexTransaction.queryIndex
@Watched(prefix = "index")
public IdHolderList queryIndex(ConditionQuery query) {
// Index query must have been flattened in Graph tx
query.checkFlattened();
// NOTE: Currently we can't support filter changes in memory
if (this.hasUpdate()) {
throw new HugeException("Can't do index query when " +
"there are changes in transaction");
}
// Can't query by index and by non-label sysprop at the same time
List<Condition> conds = query.syspropConditions();
if (conds.size() > 1 ||
(conds.size() == 1 && !query.containsCondition(HugeKeys.LABEL))) {
throw new HugeException("Can't do index query with %s and %s",
conds, query.userpropConditions());
}
// Query by index
query.optimized(OptimizedType.INDEX);
if (query.allSysprop() && conds.size() == 1 &&
query.containsCondition(HugeKeys.LABEL)) {
// Query only by label
return this.queryByLabel(query);
} else {
// Query by userprops (or userprops + label)
return this.queryByUserprop(query);
}
}
会先做一些检查，然后判断是否有属性条件，如果没有则直接查询对应label，否则走queryByUserprop，根据属性值查询结果。
@Watched(prefix = "index")
private IdHolderList queryByUserprop(ConditionQuery query) {
// Get user applied label or collect all qualified labels with
// related index labels
Set<MatchedIndex> indexes = this.collectMatchedIndexes(query);
if (indexes.isEmpty()) {
Id label = query.condition(HugeKeys.LABEL);
throw noIndexException(this.graph(), query, label);
}
// Value type of Condition not matched
boolean paging = query.paging();
if (!validQueryConditionValues(this.graph(), query)) {
return IdHolderList.empty(paging);
}
// Do index query
IdHolderList holders = new IdHolderList(paging);
for (MatchedIndex index : indexes) {
for (IndexLabel il : index.indexLabels()) {
validateIndexLabel(il);
}
if (paging && index.indexLabels().size() > 1) {
throw new NotSupportException("joint index query in paging");
}
if (index.containsSearchIndex()) {
// Do search-index query
holders.addAll(this.doSearchIndex(query, index));
} else {
// Do secondary-index, range-index or shard-index query
IndexQueries queries = index.constructIndexQueries(query);
assert !paging || queries.size() <= 1;
IdHolder holder = this.doSingleOrJointIndex(queries);
holders.add(holder);
}
/*
* NOTE: need to skip the offset if offset > 0, but can't handle
* it here because the query may a sub-query after flatten,
* so the offset will be handle in QueryList.IndexQuery
*
* TODO: finish early here if records exceeds required limit with
* FixedIdHolder.
*/
}
return holders;
}
queryByUserprop 会先查询出匹配的索引(collectMatchedIndexes)，如果没匹配到索引，就会报错。
如果匹配到多个索引，依次查询，如果是search索引，走doSearchIndex，反之先constructIndexQueries，然后doSingleOrJointIndex。
搜索索引
搜索索引，之所以特殊处理，因为要分词：
@Watched(prefix = "index")
private IdHolderList doSearchIndex(ConditionQuery query,
MatchedIndex index) {
query = this.constructSearchQuery(query, index);
// Sorted by matched count
IdHolderList holders = new SortByCountIdHolderList(query.paging());
List<ConditionQuery> flatten = ConditionQueryFlatten.flatten(query);
for (ConditionQuery q : flatten) {
if (!q.noLimit() && flatten.size() > 1) {
// Increase limit for union operation
increaseLimit(q);
}
IndexQueries queries = index.constructIndexQueries(q);
assert !query.paging() || queries.size() <= 1;
IdHolder holder = this.doSingleOrJointIndex(queries);
// NOTE: ids will be merged into one IdHolder if not in paging
holders.add(holder);
}
return holders;
}
- 先构造查询，然后组合结果
- 重点是如何构造查询的
private ConditionQuery constructSearchQuery(ConditionQuery query,
MatchedIndex index) {
ConditionQuery originQuery = query;
Set<Id> indexFields = new HashSet<>();
// Convert has(key, text) to has(key, textContainsAny(word1, word2))
for (IndexLabel il : index.indexLabels()) {
if (il.indexType() != IndexType.SEARCH) {
continue;
}
Id indexField = il.indexField();
String fieldValue = (String) query.userpropValue(indexField);
Set<String> words = this.segmentWords(fieldValue);
indexFields.add(indexField);
query = query.copy();
query.unsetCondition(indexField);
query.query(Condition.textContainsAny(indexField, words));
}
// Register results filter to compare property value and search text
query.registerResultsFilter(elem -> {
for (Condition cond : originQuery.conditions()) {
Object key = cond.isRelation() ? ((Relation) cond).key() : null;
if (key instanceof Id && indexFields.contains(key)) {
// This is an index field of search index
Id field = (Id) key;
assert elem != null;
HugeProperty<?> property = elem.getProperty(field);
String propValue = propertyValueToString(property.value());
String fieldValue = (String) originQuery.userpropValue(field);
if (this.matchSearchIndexWords(propValue, fieldValue)) {
continue;
}
return false;
}
if (!cond.test(elem)) {
return false;
}
}
return true;
});
return query;
}
- 先分词
- 然后resetquery，Convert has(key, text) to has(key, textContainsAny(word1, word2))
- 最后，索引查询可能匹配到多个结果，registerResultsFilter 注册一个结果过滤器，对结果做过滤
普通索引
普通索引，也是先构造索引查询：
ublic IndexQueries constructIndexQueries(ConditionQuery query) {
// Condition query => Index Queries
if (this.indexLabels().size() == 1) {
/*
* Query by single index or composite index
*/
IndexLabel il = this.indexLabels().iterator().next();
ConditionQuery indexQuery = constructQuery(query, il);
assert indexQuery != null;
return IndexQueries.of(il, indexQuery);
} else {
/*
* Query by joint indexes
*/
IndexQueries queries = buildJointIndexesQueries(query, this);
assert !queries.isEmpty();
return queries;
}
}
如果只匹配到一个索引，直接走这个索引，最简单的情况，
如果匹配到多个索引，这个时候要走联合查询了（buildJointIndexesQueries）
最后，通过doSingleOrJointIndex来获取结果：
@Watched(prefix = "index")
private IdHolder doSingleOrJointIndex(IndexQueries queries) {
if (queries.size() == 1) {
return this.doSingleOrCompositeIndex(queries);
} else {
return this.doJointIndex(queries);
}
}
如果queries.size > 1，代表要走联合索引。但是一般db一次查询通常直走一个索引，hugegraph也差不多：
@Watched(prefix = "index")
private IdHolder doJointIndex(IndexQueries queries) {
if (queries.oomRisk()) {
LOG.warn("There is OOM risk if the joint operation is based on a " +
"large amount of data, please use single index + filter " +
"instead of joint index: {}", queries.rootQuery());
}
// All queries are joined with AND
Set<Id> intersectIds = null;
boolean filtering = false;
IdHolder resultHolder = null;
for (Map.Entry<IndexLabel, ConditionQuery> e : queries.entrySet()) {
IndexLabel indexLabel = e.getKey();
ConditionQuery query = e.getValue();
assert !query.paging();
if (!query.noLimit() && queries.size() > 1) {
// Unset limit for intersection operation
query.limit(Query.NO_LIMIT);
}
/*
* Try to query by joint indexes:
* 1 If there is any index exceeded the threshold, transform into
* partial index query, then filter after back-table.
* 1.1 Return the holder of the first index that not exceeded the
* threshold if there exists one index, this holder will be used
* as the only query condition.
* 1.2 Return the holder of the first index if all indexes exceeded
* the threshold.
* 2 Else intersect holders for all indexes, and return intersection
* ids of all indexes.
*/
IdHolder holder = this.doIndexQuery(indexLabel, query);
if (resultHolder == null) {
resultHolder = holder;
}
assert this.indexIntersectThresh > 0; // default value is 1000
Set<Id> ids = ((BatchIdHolder) holder).peekNext(
this.indexIntersectThresh).ids();
if (ids.size() >= this.indexIntersectThresh) {
// Transform into filtering
filtering = true;
query.optimized(OptimizedType.INDEX_FILTER);
} else if (filtering) {
assert ids.size() < this.indexIntersectThresh;
resultHolder = holder;
break;
} else {
if (intersectIds == null) {
intersectIds = ids;
} else {
CollectionUtil.intersectWithModify(intersectIds, ids);
}
if (intersectIds.isEmpty()) {
break;
}
}
}
if (filtering) {
return resultHolder;
} else {
assert intersectIds != null;
return new FixedIdHolder(queries.asJointQuery(), intersectIds);
}
}
- 依次读取，先读取indexIntersectThresh 个数的匹配索引id，indexIntersectThresh用来控制1次读取索引id的个数，这个默认是1000,
- 如果地个数》=indexIntersectThresh，这个时候hugegraph认为匹配结果数太多了，不能直接走索引查询到结果，需要走过滤（OptimizedType.INDEX_FILTER），也就是读取可能的候选结果，然后通过查询条件过滤结果。
- 如果有一个索引较小，resultHolder缓存较小索引的
- 如果几个索引都小于indexIntersectThresh，这是最理想情况，直接取ids的交集（CollectionUtil.intersectWithModify）
读取到id后，就是根据id读取结果，过滤结果了。
如何通过索引读取到匹配的id？
关键代码在AbstractTransaction：
@Watched(prefix = "tx")
public QueryResults<BackendEntry> query(Query query) {
LOG.debug("Transaction query: {}", query);
/*
* NOTE: it's dangerous if an IdQuery/ConditionQuery is empty
* check if the query is empty and its class is not the Query itself
*/
if (query.empty() && !query.getClass().equals(Query.class)) {
throw new BackendException("Query without any id or condition");
}
Query squery = this.serializer.writeQuery(query);
// Do rate limit if needed
RateLimiter rateLimiter = this.graph.readRateLimiter();
if (rateLimiter != null && query.resultType().isGraph()) {
double time = rateLimiter.acquire(1);
if (time > 0) {
LOG.debug("Waited for {}s to query", time);
}
BackendEntryIterator.checkInterrupted();
}
this.beforeRead();
try {
return new QueryResults<>(this.store.query(squery), query);
} finally {
this.afterRead(); // TODO: not complete the iteration currently
}
}
逐级往下，核心代码在writeQueryCondition：
@Override
protected Query writeQueryCondition(Query query) {
HugeType type = query.resultType();
if (!type.isIndex()) {
return query;
}
ConditionQuery cq = (ConditionQuery) query;
if (type.isNumericIndex()) {
// Convert range-index/shard-index query to id range query
return this.writeRangeIndexQuery(cq);
} else {
assert type.isSearchIndex() || type.isSecondaryIndex() ||
type.isUniqueIndex();
// Convert secondary-index or search-index query to id query
return this.writeStringIndexQuery(cq);
}
}
如果是rangeindex 索引，会转换为scan indexlabelid:start - indexlabelid:end 的查询
private Query writeRangeIndexQuery(ConditionQuery query) {
Id index = query.condition(HugeKeys.INDEX_LABEL_ID);
E.checkArgument(index != null, "Please specify the index label");
List<Condition> fields = query.syspropConditions(HugeKeys.FIELD_VALUES);
E.checkArgument(!fields.isEmpty(),
"Please specify the index field values");
HugeType type = query.resultType();
Id start = null;
if (query.paging() && !query.page().isEmpty()) {
byte[] position = PageState.fromString(query.page()).position();
start = new BinaryId(position, null);
}
RangeConditions range = new RangeConditions(fields);
if (range.keyEq() != null) {
Id id = formatIndexId(type, index, range.keyEq(), true);
if (start == null) {
return new IdPrefixQuery(query, id);
}
E.checkArgument(Bytes.compare(start.asBytes(), id.asBytes()) >= 0,
"Invalid page out of lower bound");
return new IdPrefixQuery(query, start, id);
}
Object keyMin = range.keyMin();
Object keyMax = range.keyMax();
boolean keyMinEq = range.keyMinEq();
boolean keyMaxEq = range.keyMaxEq();
if (keyMin == null) {
E.checkArgument(keyMax != null,
"Please specify at least one condition");
// Set keyMin to min value
keyMin = NumericUtil.minValueOf(keyMax.getClass());
keyMinEq = true;
}
Id min = formatIndexId(type, index, keyMin, false);
if (!keyMinEq) {
/*
* Increase 1 to keyMin, index GT query is a scan with GT prefix,
* inclusiveStart=false will also match index started with keyMin
*/
increaseOne(min.asBytes());
keyMinEq = true;
}
if (start == null) {
start = min;
} else {
E.checkArgument(Bytes.compare(start.asBytes(), min.asBytes()) >= 0,
"Invalid page out of lower bound");
}
if (keyMax == null) {
keyMax = NumericUtil.maxValueOf(keyMin.getClass());
keyMaxEq = true;
}
Id max = formatIndexId(type, index, keyMax, false);
if (keyMaxEq) {
keyMaxEq = false;
increaseOne(max.asBytes());
}
return new IdRangeQuery(query, start, keyMinEq, max, keyMaxEq);
}
如果是其他索引，则转换为前缀匹配查询:
private Query writeStringIndexQuery(ConditionQuery query) {
E.checkArgument(query.allSysprop() &&
query.conditions().size() == 2,
"There should be two conditions: " +
"INDEX_LABEL_ID and FIELD_VALUES" +
"in secondary index query");
Id index = query.condition(HugeKeys.INDEX_LABEL_ID);
Object key = query.condition(HugeKeys.FIELD_VALUES);
E.checkArgument(index != null, "Please specify the index label");
E.checkArgument(key != null, "Please specify the index key");
Id prefix = formatIndexId(query.resultType(), index, key, true);
return prefixQuery(query, prefix);
}
查询到rocksdb后端的时候：
protected BackendColumnIterator queryBy(Session session, Query query) {
// Query all
if (query.empty()) {
return this.queryAll(session, query);
}
// Query by prefix
if (query instanceof IdPrefixQuery) {
IdPrefixQuery pq = (IdPrefixQuery) query;
return this.queryByPrefix(session, pq);
}
// Query by range
if (query instanceof IdRangeQuery) {
IdRangeQuery rq = (IdRangeQuery) query;
return this.queryByRange(session, rq);
}
// Query by id
if (query.conditions().isEmpty()) {
assert !query.ids().isEmpty();
// NOTE: this will lead to lazy create rocksdb iterator
return new BackendColumnIteratorWrapper(new FlatMapperIterator<>(
query.ids().iterator(), id -> this.queryById(session, id)
));
}
// Query by condition (or condition + id)
ConditionQuery cq = (ConditionQuery) query;
return this.queryByCond(session, cq);
}
前缀查询：
protected BackendColumnIterator queryByPrefix(Session session,
IdPrefixQuery query) {
int type = query.inclusiveStart() ?
Session.SCAN_GTE_BEGIN : Session.SCAN_GT_BEGIN;
type |= Session.SCAN_PREFIX_END;
return session.scan(this.table(), query.start().asBytes(),
query.prefix().asBytes(), type);
}
range查询：
protected BackendColumnIterator queryByRange(Session session,
IdRangeQuery query) {
byte[] start = query.start().asBytes();
byte[] end = query.end() == null ? null : query.end().asBytes();
int type = query.inclusiveStart() ?
Session.SCAN_GTE_BEGIN : Session.SCAN_GT_BEGIN;
if (end != null) {
type |= query.inclusiveEnd() ?
Session.SCAN_LTE_END : Session.SCAN_LT_END;
}
return session.scan(this.table(), start, end, type);
}
查询后，在BinarySerializer中，通过readIndex还原为index：
@Override
public HugeIndex readIndex(HugeGraph graph, ConditionQuery query,
BackendEntry bytesEntry) {
if (bytesEntry == null) {
return null;
}
BinaryBackendEntry entry = this.convertEntry(bytesEntry);
// NOTE: index id without length prefix
byte[] bytes = entry.id().asBytes();
HugeIndex index = HugeIndex.parseIndexId(graph, entry.type(), bytes);
Object fieldValues = null;
if (!index.type().isRangeIndex()) {
fieldValues = query.condition(HugeKeys.FIELD_VALUES);
if (!index.fieldValues().equals(fieldValues)) {
// Update field-values for hashed or encoded index-id
index.fieldValues(fieldValues);
}
}
this.parseIndexName(graph, query, entry, index, fieldValues);
return index;
}
parseIndexId 和parseIndexName 是存储的decode操作，代码类似，一个存，一个读。
索引与全局排序优化
这里提一个问题，要对符合条件的结果做全局排序怎么优化？
比如，我们需要按更新时间(update_time）排序，当没有其他条件时，可以将排序转换为update_time>0 的查询，因为range索引默认是有序的，从小到大（详见上面的存储结构分析）。
如果要倒序怎么办？
- 业务简单时，可以冗余一个字段，比如update_time_desc，取一个固定值-update_time, 这样最新的的数据在前面。
但是，这种查询，在有其他条件时就无效了，详见doJointIndex，这种情况如何优化了？
我们下期再聊。
感谢您的认真阅读。
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