Additional performance comparisons available in an updated post . Come see me speak about JSON and XML at SQL Saturday Columbus on July 22 ! Starting with the 2016 release, SQL Server offers native JSON support. Although the implementation is not perfect, . I am still a huge fan Even if a new feature like JSON support is awesome, I am only likely to use it if it is practical and performs better than the alternatives. Today I want to pit JSON against XML and see which is the better format to use in SQL Server. Enter XML, SQL’s Bad Hombre Full disclosure: I don’t love XML and I also don’t love SQL Server’s implementation of it. XML is too wordy (lots of characters wasted on closing tags), it has elements AND attributes (I don’t like having to program for two different scenarios), and depending on what language you are in, sometimes you need schema files and sometimes you don’t. programming SQL Server’s implementation of XML does have some nice features like a dedicated datatype that reduces storage space and validates syntax, but I find the querying of XML to be clumsy. All XML grievances aside, I am still willing to use XML if it outperforms JSON. So let’s run some test queries! Is JSON SQL Server’s New Sheriff in Town? Although performance is the final decider in these comparison tests, I think JSON has a head start over XML purely in terms of usability. SQL Server’s JSON function signatures are easier to remember and cleaner to write on screen. The test data I’m using is vehicle year/make/model data from . Here’s what it looks like once I loaded it into a table called : https://github.com/arthurkao/vehicle-make-model-data dbo.XmlVsJson CREATE TABLE dbo.XmlVsJson(Id INT IDENTITY PRIMARY KEY,XmlData XML,JsonData NVARCHAR(MAX)) ( if you want to play along at home) The full data query is available in this gist Data Size So XML should be larger right? It’s got all of those repetitive closing tags? SELECTDATALENGTH(XmlData)/1024.0/1024.0 AS XmlMB,DATALENGTH(JsonData)/1024.0/1024.0 AS JsonMBFROMdbo.XmlVsJson Turns out the XML is actually smaller! How can this be? This is the magic behind the . SQL doesn’t store XML as a giant string; it stores only the , leading to a reduction in space. SQL Server XML datatype XML InfoSet The JSON on the other hand is stored as regular old nvarchar(max) so its full string contents are written to disk. XML wins in this case. INSERT Performance So XML is physically storing less data when using the XML data type than JSON in the nvarchar(max) data type, does that mean it will insert faster as well? Here’s our query that tries to insert 100 duplicates of the row from our first query: SET STATISTICS TIME ON INSERT INTO dbo.XmlVsJson (XmlData)SELECT XmlData FROM dbo.XmlVsJsonCROSS APPLY(SELECT DISTINCT numberFROM master..spt_valuesWHERE number BETWEEN 1 AND 100)t WHERE Id = 1GO INSERT INTO dbo.XmlVsJson (JsonData)SELECT JsonData FROM dbo.XmlVsJsonCROSS APPLY(SELECT DISTINCT numberFROM master..spt_valuesWHERE number BETWEEN 1 AND 100)t WHERE Id = 1GO And the results? Inserting the 100 XML rows took 613ms on my machine, while inserting the 100 JSON rows took 1305ms… XML wins again! JSON ain’t looking too hot. Wait for it… I’m guessing since the XML data type physically stores less data, it makes sense that it would also write it out to the table faster as well. CRUD Operations — but how does it compare to XML on ? I’m incredibly impressed by SQL Server’s JSON performance when compared to .NET SQL Server Read Let’s select the fragment for our second car from our XML and JSON: SELECT t.XmlData.query('/cars/car[2]')FROM dbo.XmlVsJson tWHERE Id = 1 SELECT JSON_QUERY(t.JsonData, '$.cars[1]')FROM dbo.XmlVsJson tWHERE Id = 1 Result? (at 0ms vs 63ms for XML) when needing to pluck out a fragment from our larger object string. JSON wins What if we want to grab a specific value instead of a fragment? SELECT t.XmlData.value('(/cars/car[2]/model)[1]', 'varchar(100)') FROM dbo.XmlVsJson tWHERE Id = 1 SELECT JSON_VALUE(t.JsonData, '$.cars[1].model')FROM dbo.XmlVsJson tWHERE Id = 1 Once again with 0ms vs 11ms for XML. JSON wins If you look at the execution plans for these last two queries, it’s easy to see that XML has a lot more to do behind the scenes to retrieve the data: XML: JSON: Create We saw above that inserting rows of XML data is faster than inserting rows of JSON, but what if we want to insert new data into the object strings themselves? Here I want to insert the property “mileage” into the first car object: UPDATE t SET XmlData.modify('insert <mileage>100,000</mileage>into (/cars/car[1])[1]')FROM dbo.XmlVsJson tWHERE Id = 1 UPDATE t SET JsonData = JSON_MODIFY(JsonData,'$.cars[0].mileage','100,000')FROM dbo.XmlVsJson tWHERE Id = 1 In addition to the cleaner syntax ( is essentially the same as a ) the JSON insert runs in 22ms compared to the 206ms for XML. JSON_MODIFY() REPLACE() Another JSON win. Update Let’s update the mileage properties we just added to have values of 110,000: UPDATE t SET XmlData.modify('replace value of (/cars/car[1]/mileage/text())[1]with "110,000"')FROM dbo.XmlVsJson tWHERE Id = 1 UPDATE t SET JsonData = JSON_MODIFY(JsonData, '$.cars[0].mileage','110,000')FROM dbo.XmlVsJson tWHERE Id = 1 Result? and was able to perform this update in 54ms vs XML’s 194ms. JSON has the quicker draw Delete Deleting large string data, a DBA’s dream *snicker*. Let’s delete the mileage property, undoing all of that hard work we just did: UPDATE t SET XmlData.modify('delete /cars/car[1]/mileage[1]')FROM dbo.XmlVsJson tWHERE Id = 1 UPDATE t SET JsonData = JSON_MODIFY(JsonData, '$.cars[0].mileage', null)FROM dbo.XmlVsJson tWHERE Id = 1 50ms to 159ms. JSON doesn’t take any time to reload and wins against XML again Read Part 2: Indexes So above we saw that JSON was faster than XML at reading fragments and properties from a single row of serialized data. But our SQL Server’s probably have LOTS of rows of data — how well does indexed data parsing do in our match up? First let’s expand our data — instead of storing all of our car objects in a single field, let’s build a new table that has each car on its own row: (once again, if you are playing along at home) full dataset at GitHub Now that we have our expanded data in our table, let’s add some indexes. The XML datatype in SQL Server has its own types of indexes, while . JSON simply needs a computed column with a regular index applied to it DROP INDEX IF EXISTS PXML_XmlData ON XmlVsJson2CREATE PRIMARY XML INDEX PXML_XmlDataON XmlVsJson2 (XmlData); ALTER TABLE dbo.XmlVsJson2ADD MakeComputed AS JSON_VALUE(JsonData, '$.make')CREATE NONCLUSTERED INDEX IX_JsonData ON dbo.XmlVsJson2 (MakeComputed) (Note: I also tried adding an XML secondary index for even better performance, but I couldn’t get the query engine to use that secondary index on such a basic dataset) If we try to find all rows that match a predicate: SELECT Id, XmlDataFROM dbo.XmlVsJson2 tWHERE t.XmlData.exist('/car/make[.="ACURA"]') = 1 SELECT Id, JsonDataFROM dbo.XmlVsJson2 tWHERE JSON_VALUE(t.JsonData, '$.make') = 'ACURA' XML is able to filter out 96 rows in 200ms and JSON accomplishes the same in 9ms. . A final win for JSON Conclusion If you need to store and manipulate serialized string data in SQL Server, there’s no question: JSON is the format of choice. Although JSON’s storage size is a little larger than its XML predecessor, SQL Server’s JSON functions outperform XML in speed in nearly all cases. Is there enough performance difference to rewrite all of your old XML code to JSON? Probably not, but every case is different. One thing is clear: new development should consider taking advantage of SQL Server’s new JSON functions. 💚 Enjoyed this post? Please recommend it by giving it a green heart below. Do you still plan on using XML instead of JSON for new development in SQL Server 2016+? I’d be curious to know why in the comments below.
