Mongodb Compound Index Unique







This is a (presumably) simple use case: A window displays a single document from a collection with a compound index. The shard-key must be part of an index and it must be the first field in that index. MongoDB lets users specify between indexes and that prevents applications from duplicating values into inserted fields and a number of other issues that can possibly arise. Welcome to the fourth chapter of the MongoDB tutorial (part of the MongoDB Developer and Administrator Course). It is a simple example of crud operation in laravel 5. It uses a unique, compound index on the chunks collection using the files_id and n fields. Hashed indexes do not support arrays. Users can specify secondary indexes on any field, compound indexes, geospatial, text, sparse, TTL, and others. A value of 1 indicates an ascending sort order. This index prevents clients from inserting two documents having the same _id value. Composite SQL Server Index. According to MongoDB docs on Compound Indexes. If there are no values assigned to the index, MongoDB creates an _id field with an ObjectId value. See the MongoDB manual for a more detailed explanation of sharding. • MongoDB Indexes • Index Types - 1 • Index Types - 2 The order of fields listed in a compound index has significance. If we try to do this, MongoDB will tell that it can’t index parallel arrays and the reason is that there’s an explosion of index points that create it because it has to create index points for the cartesian product of the items in the array and it doesn’t permit that. To create such an index, use the unique option. Ops Manager maintains the availability of the cluster by taking one node out of the cluster at a time, starting with the primary, building its index, and adding it back to the cluster. My database reach 15Go of data and 20GO of indexes. MongoDB supports a user-defined index on multiple fields as well. One of the most powerful features of MongoDB is its rich indexing functionality. There can be no unique index unless the shard-key is part of it and is then the first field. This is a (presumably) simple use case: A window displays a single document from a collection with a compound index. Handler_read_first and handler_read_last may shed some more light onto what kind of index scans those are - if we are talking about full index scan (forward or backward), those two counters will be updated. MongoDB creates a unique index on the _id field during the creation of a collection. Key info about MongoDB’s indexes • A collection may have at most 64 indexes. If a compound index is specified as unique, the combination of values must be unique. MongoDB provides full index support, including secondary, compound, and geospatial indexes. The index of the _id field contains the Unique property. For more information about slow queries, see Performance Advisor. In many ways, you can think of the shard key a cluster-wide index. 2, for featureCompatibilityVersion (fCV) of 4. Normally we work with indexes directly in the mongo shell. 4, for multikey indexes created using MongoDB 3. Data that's added to the container and the throughput that you provision on the container are automatically (horizontally) partitioned across a set of logical partitions. com See also the IRC channel -- freenode. The sparse index property can be combined with the unique index property to skip Docs with duplicate values for a field but ignore those without an indexed key. The order of fields listed in a compound index has significance. Compound Index. Bear in mind that indexes are stored separately in RAM from the data they index and aren’t clustered. When access control, i. of slower wri te operation, disk and memory usage. Multikey Index. But MongoDB does not enforce consistency in this case. Supported indexing strategies such as compound, unique, array, partial, TTL, geospatial, sparse, hash, wildcard and text ensure optimal performance for multiple query patterns, data types, and application requirements. To create an index, you just specify the field that should be indexed, and specify if you want the index to be ascending (1) or descending (-1). You should go with option 1. You can leave the default index structure in place or define one of your own. I am using the C++ driver but using the shell here for illustration. To index a field that holds an array value, MongoDB creates an index key for each element in the array. wire protocol support for MongoDB API api-for-mongo-treats-multikey-unique-indexes. To post to this group, send email to [email protected] remove and add an instance from a mongodb replica set; add an arbiter in a mongodb replica set; Mongodb mongod start and stop; Mongodb sparse index; Mongodb unique index; Mongodb compound index; Mongodb index on single field; move collection between databases in mongodb; More ←. to make old cells younger and extend their life-cycle. Better support for compound indexes The 2d index can only be used in a compound index if 1. x supports ACID transactions and makes the technology an asset for enterprises across the IT and fintech sectors. This is because MongoDB creates a unique index on the _id field during the creation of a collection. Starting in MongoDB 3. com/4211/creating-unique-key-index-mongodb/ We have learnt how to create a key/index so far - today lets learn how to create unique key/inde. In the previous article, we discussed the advanced index concept MongoDB. Reads done without specifying the shard-key will lead to requests to all the different shards. If there is already data in the database which is not unique one has to ensure its uniqueness before one is able to create the unique-index. Please note that we cannot drop this Index, as it's the default. xml slides. For example, to create a unique index on groupNumber, lastname, and firstname fields of the members collection, use the following operation in the. 6 CRUD Tutorial With Example From Scratch. MongoDB indexes only the first occurrence of a. These multikey indexes support efficient queries against array fields. Introducing MongoDB Text Search. 6, MongoDB has support for full text indexes to enable faster text pattern searches. MongoDB supports aggregation pipeline which helps us to build complex aggregations to optimize the database. To run on 32-bits systems, you should have at least 4GB of memory. A compound key is a composite key for which each attribute that makes up the key is a simple key in its own right. }} I need a general way to traverse the index from a point on the index. The _id index prevents clients from inserting two documents with the same value for the _id field. While still combined together as L-Carnosine it has the unique ability to rejuvenate cells i. I believe these indexes solve a problem for users who are temporarily forced to use MongoDB with data structured as it was from a legacy key-value store. MongoDB Indexing Part 2 Multi Term Query, Drop Index, Nested Fields, Indexing on an array, Unique Index, Compound indexes, Covering Index, Dead Weight Index, Background built Index, 2 Oct 2016. Also, $or. Making MongoDB working does not mean that understanding the details of MongoDB. By default, the new index uses dynamic field mappings, which allows Full Text Search to dynamically assign data types to fields. However it's less great that the empty array is given a special 'undefined' value. If I make an index with "anonymous" first, Mongo can jump straight to the section of the index with signed comments, then do a range-scan from timestamp 2 to 4. (8 replies) Hi, I'm new in using Mongo with big data and indexes. The values for regular index fields indicates sort order: 1 for ascending, or -1 for descending sort order. In version 2. But under the hood the mongo-tenant creates an indexed field (tenantId by default) and includes this in all defined unique indexes. unique - Optonal boolean type parameter, Specify true to create a unique index. For example, this could be a case when index is based on a time/date field. The keys of the JSON document are the fields to be indexed, the values define the index direction (1 for ascending, -1 for descending). ensureIndex( { "user_id": 1 }, { unique: true } ) By default, unique is false on MongoDB indexes. MySQL allows you to create a composite index that consists of up to 16 columns. Index in SQL Server 2008 May 27, 2011. MongoDB will use the compound index in all of the situations that it would have used the prefix index. If not specified, the name will be derived from the key pattern. The "replaceDocument" works great when we are dealing with only default "_id" unique index. Having extensive indexing functionality makes it easier for developers to build apps that provide rich functionality and low latency. is the name of a variable that forms the index or the name you choose for a composite index. In version 2. MongoDB creates a unique index on the _id field during the creation of a collection. The sparse index property can be combined with the unique index property to skip Docs with duplicate values for a field but ignore those without an indexed key. For example, to create a unique index on groupNumber, lastname, and firstname fields of the members collection, use the following operation in the. Creates a unique index so that the collection will not accept insertion of documents where the index key or keys match an existing value in the index. Compound Indexes are created on two or more columns. A unique index does not allow duplicate value in the field. find( {} ). The syntax to disable the Primary Key using the ALTER INDEX statement in SQL Server (Transact-SQL) is following. We will cover how to manage related data with embedding and referencing, we'll touch on. Compounding unique indexes with less selective fields can not further increase that maximum. "unique" Specify TRUE to create a unique index. The _Id() field is stored with each of the document (row) in a Collection (table). We then met special index types such as the TTL, unique, and sparse index. { a: 1, b: 1 } and { a: 1 }), if neither index has a sparse or unique constraint, then you can remove the index on the prefix (e. MongoDB supports generic secondary indexes and provides unique, compound, geospatial, and full-text indexing capabilities as well. For instance, if a compound index consists of {"education": 1, "password": -1 }, the index sorts first by education and then, within each education value, sort by password. The order of fields listed in a compound index has significance. To run on 32-bits systems, you should have at least 4GB of memory. In terms of performance the difference will be small at best. Index name of the index to be created either as plain value or as template expression. It helps in the process of no duplication in tables. In general, MongoDB encourages embedding of data instead of relations, because this allow to get all relevant data with a single query. During this we face three major difficulties: This package strives to facilitate at these points by wrapping official mongodb package. Using MongoDB full-text search, you can define a text index on any field in the document whose value is a string or an array of strings. Better support for compound indexes The 2d index can only be used in a compound index if 1. Highlights Strengthens national footprint as the fastest-growing co-living company with 700+ buildings, 40,000+ beds OYO LIFE is present in 9 cities - Delhi, Noida, Gurgao. [mongodb-user] collection. Adding more indexes just slows down find (), update () and remove () queries. This chapter will explain how to create and manage different types of indexes in MongoDB to execute queries faster. If you create an index which contains all the fields you would query and all the fields that will be returned by that query, MongoDB will never need to read the data because it’s all contained within the index. When you apply a unique index to an embedded document, MongoDB treats it as unique in the collection. For instance, if a compound index consists of {"education": 1, "password": -1 }, the index sorts first by education and then, within each education value, sort by password. We are trying to do "upsert" to documents in MongoDB which have a unique index (both single column and composite index). You can also enforce a unique constraint on compound indexes. Introduction It’s like a catalogue of a book. For example, to create a unique index on groupNumber, lastname, and firstname fields of the members collection, use the following operation in the. For compound indexes order matters as we match from left to right. Try to write queries that use 1 (compounded) index per query. We want to creat a compound index in a sharded collection with a hashed sharding key. This is a (presumably) simple use case: A window displays a single document from a collection with a compound index. A prefix of a _____ index is a subset that consists of one or more keys at the start of the index key pattern. MongoDB lets users specify between indexes and that prevents applications from duplicating values into inserted fields and a number of other issues that can possibly arise. For example, a compound index defined as {firstName:1, age:-1} will sort data by firstName first and then each firstName with age. a) unique b) primary MongoDB will use the compound. will the index creation succeed or fail. Note: We are hosting a webinar on July 12, 2017, where I will talk about MongoDB indexes and how to choose a good indexing plan. A unique index can also be a compound embedded field or embedded document index. The default value is FALSE. Compound Indexes. The MongoDB Java Driver provides the Indexes class that includes static factory methods to create index specification documents for the various MongoDB Index key types. Default _ID Each MongoDB collection contains a builtin index on the _id field of the collection. Indexes can be defined for any key or array within the document, as secondary indexes MongoDB indexing will be familiar to DBAs - B-Tree Indexes, Secondary Indexes As with a relational DB, indexes are the single biggest tunable performance factor - Define indexes by identifying common queries - Use MongoDB explain to ensure index coverage - Use. In the previous post we looked at compound indexes in MongoDb. More information about sorting compound indexes can be found in the MongoDB docs. index: array of documents: Each array element is a document that specifies a key in the index and its sort order, ascending or descending. Compound indexes are specified by a comma-separated list of paths. They do not need to have the same set of fields or structure, and common fields in a col. Default _id Index¶ MongoDB creates a unique index on the _id field during the creation of a collection. Handler_read_next and handler_read_prev - those two counters are updated whenever MySQL does an index scan - forward or backward. If you use the unique constraint on a compound index then MongoDB will enforce uniqueness on the combination of values, rather than the individual value for any or all values of the key. Your other options do not avoid this problem, they just shift it from the _id index to the secondary unique index - but now you have two indexes, once that's right-balanced and the other one that's random access. During this we face three major difficulties: This package strives to facilitate at these points by wrapping official mongodb package. For: instance, if a compound index consists of ``{ userid: 1, score: -1 }``,. UNIQUE constraints are also indexed by default, but the default index for a UNIQUE constraint is a non. Normally we work with indexes directly in the mongo shell. For sharded collections, as per MongoDB behavior, creating a unique index requires providing the shard (partition) key. MongoDB concepts. MOngoDB GridFS uses indexes on each of the chunks and files collections for efficiency. A shard key consists of one or more indexed fields that exist in every document within a collection. A value of 1 indicates an ascending sort order. You might wanna check the following post also: How to apply constraints in MongoDB?. Compound Indexes are created on two or more columns. Besides a regular one field index, you can also create the following indexes in. Index options for MongoDB include: Compound Indexes Geospatial Indexes Text Search Indexes Unique Indexes Array Indexes TTL Indexes Sparse Indexes Hash Indexes MongoDB also supports index intersection, allowing the use of multiple indexes to fulfill a query. For usage on nested or embedded structures the provided name will be prefixed with the path leading to the entity. How to show indexes and drop index in Mongodb lets learn about MongoDB - Advanced Indexing options Indexing with MongoDB is done using. Normally we work with indexes directly in the mongo shell. A composite index is an index on multiple columns. When access control, i. compound indexes. Specify true to create a unique index. This blog explores the different types of indexes and reviews some things you should consider when setting up one. Creating Indexes in MongoDB. Compounding unique indexes with less selective fields can not further increase that maximum. One way to get around this is by using a compound track-by expression that results in a set-wide unique value. name (string) – Specify the name of the index. Building indexes this way reduces the performance impact of building indexes on replica sets and sharded clusters. To take advantage of the optimizations provided by Cosmos DB indexing techniques, we recommend creating multiple individual indexes instead of a single (non-unique) compound index. To maintain cluster availability, Atlas removes one node from the cluster at a time starting with a secondary. When no suitable index is available, MongoDB is forced to do without. Basically mongo's unique indexes can't be used on polymorphic. Ask Question Asked 6 years, Browse other questions tagged c#. This operation drops all indexes, including the _id index, and then rebuilds all indexes. Compound Index. cache (Boolean) – Specify false to prevent caching of this db. remove and add an instance from a mongodb replica set; add an arbiter in a mongodb replica set; Mongodb mongod start and stop; Mongodb sparse index; Mongodb unique index; Mongodb compound index; Mongodb index on single field; move collection between databases in mongodb; More ←. My database reach 15Go of data and 20GO of indexes. is a list of variables to use in making a composite index. friend_id by friends_id but i'm experiencing the same issue !!!! 2011/10/20 Robert Stam -- You received this message because you are subscribed to the Google Groups "mongodb-user" group. When you apply a unique index to an embedded document, MongoDB treats it as unique in the collection. In version 2. Create a compound index on the studentId and class fields of the students collection. Hashed indexes cannot be compound indexes. Text indexes can include any field whose value is a string or an array of string elements. Read more about quizzes below. A composite Index is an Index on two or more columns of a table. MongoDB creates base indexes, composite indexes, unique indexes, and optimizations First, the index MongoDB provides a variety of index support, index information is stored in system. Users can specify secondary indexes on any field, compound indexes, geospatial, text, sparse, TTL, and others. MongoDB supports 2d indexes that store points on a two-dimensional plane. Packed with many features that have become essential for many different types of software professional and incredibly easy to use, this cookbook contains more than 100 recipes to address the everyday. In the previous post we looked at compound indexes in MongoDb. Index options for MongoDB include: Compound Indexes Geospatial Indexes Text Search Indexes Unique Indexes Array Indexes TTL Indexes Sparse Indexes Hash Indexes MongoDB also supports index intersection, allowing the use of multiple indexes to fulfill a query. With one exception. For sharded collections, as per MongoDB behavior, creating a unique index requires providing the shard (partition) key. Users can specify secondary indexes on any field, compound indexes, geospatial, text, sparse, TTL, and others. mongodb-user+ [email protected] The default value is FALSE. In the previous article, we discussed about the basic index concept in MongoDb. 对于编制了索引的字段,唯一索引用于确保没有两个或两个以上的文档包含同一值。. The dictionary is guaranteed to contain at least a single key, "key" which is a list of (key, direction) pairs specifying the index (as passed to create_index()). MongoDB sorts results based on the field order in the index. In case you want to rebuild your Index MongoDB provide the reIndex() method to do so. If you use the unique constraint on a compound index (page 11), then MongoDB will enforce uniqueness on the. On the other hand, there might be a gain, however slight, from Mongo being able to toss out non-matching documents (i. In this part, we will start to put documents into action by discussing schema design. Unique indexes: When MongoDB has specifies that index is unique, it rejects inserts of new documents with an existing value for the field for which the unique index has been created. For this MongoDB has a compound index. If unspecified, MongoDB generates an index name by concatenating the names of the indexed fields and the sort order. mycollection. A composite Index is an Index on two or more columns of a table. MOngoDB GridFS uses indexes on each of the chunks and files collections for efficiency. {name: 'foo'} Specify a custom name for this index. MongoDB allows to index any type of field in a document. When defining a composite index, you specify:. ensureIndex ( { main_ingredient : 1 } ) //. Consider the Index Concepts page for more information on indexes and compound indexes. This is a (presumably) simple use case: A window displays a single document from a collection with a compound index. Two Greek words, bios (life) and logos (discourse), explain the. Indexing - MongoDB provides secondary indexes, which are implemented as B-trees and also provides unique, compound, full-text indexing capabilities as well. Using unique key property of mongoose schema we can avoid column level duplicate value. commands, MongoDB shell, 24 comments in blog (example), 174–75 compatibility of MongoDB, 9 complex data structures, 6 composite indexes, 13 compound indexing, 79, 234 compound keys, 43 compound primary keys, 10 cond parameter (group), 57 conditional operators, 57–65 with PHP driver, 111–18 with PyMongo, 148–53, 155. These indexes are separate from default "_id" index. Mongodb add index keyword after analyzing the system lists the list of keywords related and the list of websites with related content, in addition you can see which keywords most interested customers on the this website. A little explanation of Compound Indexes. To take advantage of the optimizations provided by Cosmos DB indexing techniques, we recommend creating multiple individual indexes instead of a single (non-unique) compound index. For the index part we will talk about the different types used in MongoDB comparing them with the indexes used in a relational database. One of the most powerful features of MongoDB is its rich indexing functionality. a) The unique constraint on indexes ensures that only one document can have a value for a field in a collection b) MongoDB support creating new unique indexes in sharded collections c) If you use a compound shard key, you cannot enforce uniqueness on the combination of component keys in the shard key. This option applies only to ascending/descending indexes. Now, in MongoDB, indexes are b-trees and they have an ordering, and that. MongoDB supports 2d indexes that store points on a two-dimensional plane. With the above mapping a MongoDB index will be automatically created for you. 对于编制了索引的字段,唯一索引用于确保没有两个或两个以上的文档包含同一值。. Each collection can only have one shard key. MongoDB enforces uniqueness on the entire key combination, and not individual components of the shard key. To maintain cluster availability, Atlas removes one node from the cluster at a time starting with a secondary. Index는 MongoDB에서 데이터 쿼리를 더욱 효율적으로 할 수 있게 해줍니다. createIndex( { "name": 1 }, { unique: true } ) This will create a unique index on a book's name. For instance, if a compound index consists of {"education": 1, "password": -1 }, the index sorts first by education and then, within each education value, sort by password. If you have a collection that has both a compound index and an index on its prefix (e. unique: It creates a unique index so that the collection will not accept insertion or update of documents where the index key value matches an existing value in the index. The order of fields listed in a compound index has significance. MongoDB will automatically create the _id field and assign a unique value if the value is not be specified when the document is. The actual index definition in JSON format. Unique indexes: When MongoDB has specifies that index is unique, it rejects inserts of new documents with an existing value for the field for which the unique index has been created. Default _id Index¶ MongoDB creates a unique index on the _id field during the creation of a collection. For example, to create a unique index on groupNumber, lastname, and firstname fields of the members collection, use the following operation in the. We are building the simple app that has image and datepicker as an input type and stores it in a database. You can create a unique index that will enable uniqueness of the index field value. If we try to do this, MongoDB will tell that it can’t index parallel arrays and the reason is that there’s an explosion of index points that create it because it has to create index points for the cartesian product of the items in the array and it doesn’t permit that. Creating Indexes in MongoDB. Ayrıca duplicate dropping (kopyaları yok et) olanağı ile birlikte, tekrar eden değerlerin silinmesi de sağlanabilir. A unique index causes MongoDB to reject all documents that contain a duplicate value for the indexed field To create a unique index, use the unique option to true, like: db. Basically mongo's unique indexes can't be used on polymorphic. The chunks index. multikey index : MongoDB uses multikey indexes to index the content stored in arrays. Handler_read_first and handler_read_last may shed some more light onto what kind of index scans those are - if we are talking about full index scan (forward or backward), those two counters will be updated. MongoDB Indexing Part 2 Multi Term Query, Drop Index, Nested Fields, Indexing on an array, Unique Index, Compound indexes, Covering Index, Dead Weight Index, Background built Index, 2 Oct 2016. Adding more indexes just slows down find(), update() and remove() queries. text static helper method. To unsubscribe from this group and stop receiving emails from it, send an email to [email protected] Note: When MongoDB indexes a field, if a document does not have a value for the field, a NULL value is indexed. Limitations of MongoDB It is prescribed to run MongoDB on 64-bits machines. A unique index can also be a compound embedded field or embedded document index. text static helper method. Index는 MongoDB에서 데이터 쿼리를 더욱 효율적으로 할 수 있게 해줍니다. expireAfterSeconds: Specifies a value, in seconds, to control how long MongoDB retains documents in this collection. During this we face three major difficulties: This package strives to facilitate at these points by wrapping official mongodb package. Single Field - MongoDB supports the creation of user-defined ascending/descending indexes on a single field of a document. This is the default index which will be created by MongoDB when you create a new collection. MongoDB allows up to 31 fields which can be included in the compound index. If you index a field that holds an array value, MongoDB creates separate index entries for every element of the array. For usage on nested or embedded structures the provided name will be prefixed with the path leading to the entity. name (string) – Specify the name of the index. The shard-key must be part of an index and it must be the first field in that index. MongoDB supports compound indexes, where a single index structure. Types of Indexes. In this two-part series, I'm going to explain explain. Every RethinkDB query. In this case, each unique combination of the three values within a given CompanyID is allowed. But under the hood the mongo-tenant creates an indexed field (tenantId by default) and includes this in all defined unique indexes. Array Indexes. Any field can be used for a secondary index, including fields within arrays. 다음 명령은 student_id 및 university 필드에서 고유 인덱스로 분할된 컬렉션 coll (분할 키는 university )을 만듭니다. You can change your ad preferences anytime. You can always discover total index size by looking at the results of the stats command. For example, if a compound index consists of {"name":1,"city":1}), then the index will sort first the name and then the city. authorization, is enabled, MongoDB requires all clients to authenticate themselves in order to determine their access. [mongodb-user] GridFS chunks index cannot be a background index [mongodb-user] MongoDB: sharded systems cannot enforce cluster-wide unique indexes [mongodb-user] Unique index as part of the shard key [mongodb-user] Replica set keeps crashing with duplicate key? [mongodb-user] Compound indexes and prefixes, and the effect of 'unique'. It uses a unique, compound index on the chunks collection using the files_id and n fields. mongodb-user+ [email protected] MongoDB can create an index as unique. For usage on nested or embedded structures the provided name will be prefixed with the path leading to the entity. MongoDB - Indexing and Aggregation Tutorial. This property ensures that only the indexes of Docs with indexed fields are included. The order of the fields listed in a compound index is important. On the other hand, indexes have associated costs that include memory usage, disk usage and slower updates. MongoDB allows up to 31 fields which can be included in the compound index. creating a compound index in c#. One way to get around this is by using a compound track-by expression that results in a set-wide unique value. MongoDB best practices advise up to 1,000 operations in a single transaction. For example, this could be a case when index is based on a time/date field. MongoDB supports a user-defined index on multiple fields as well. MongoLA - Indexing - Free download as PDF File (. Index intersection does not eliminate the need for creating compound indexes. A bigger danger is to forget what is already there, though thankfully it isn't possible to create duplicate indexes in MongoDB. If a compound index is specified as unique, the combination of values must be unique. 다음 명령은 student_id 및 university 필드에서 고유 인덱스로 분할된 컬렉션 coll (분할 키는 university )을 만듭니다. This is using. The order of the fields listed in a compound index is important. The first commercial synthesis of vanillin began with the more readily available natural compound eugenol. Compound Index¶ MongoDB also supports user-defined indexes on multiple fields, i. This is a (presumably) simple use case: A window displays a single document from a collection with a compound index. In Azure Cosmos DB, a container is the fundamental unit of scalability. If unspecified, MongoDB generates an index name by concatenating the. The _Id() field is stored with each of the document (row) in a Collection (table). MongoDB also supports user-defined indexes on multiple fields. The _id index prevents clients from inserting two documents with the same value for the _id field. It also allows you to have many other kind of indexes which include compound indexes, multi-indexes on arrays and geospatial indexes. When using MongoDB with TypeScript we usually want to save our "strongly-typed" entities into database collection and then retrieve them back at some later time. If an index isn't used, it is best to drop it. 이번 강좌는 MongoDB의 Index에 관한 내용입니다. MySQL allows you to create a composite index that consists of up to 16 columns. 注意,不能为_id域和复合索引指定TTL index,同时,MongoDB也不支持将TTL index作用于固定集合(capped collection)。一旦指定了TTL就不能通过createIndex()来修改时长了,也不能为同一个field指定多次TTL,只能是删除后重建。 unique index. creating a compound index in c#. more information on single-field indexes. This significantly reduces the need to fit all data into memory for maximum performance. It helps in the process of no duplication in tables. Data and throughput are partitioned based on the partition key you specify for the Azure Cosmos container. Any field can be used for a secondary index, including fields within arrays. Multicolumn unique indexes guarantee that each combination of values in the index key is unique. Compound Index. Consider other types of backup such as point-in-time and filesystem snapshots which not necessarily require locking. These indexes are separate from default "_id" index. For more information, see Performance Advisor.