1.8 Release Notes

MongoDB 1.8 is a drop-in replacement for 1.6, except:

replica set nodes should be upgraded in a particular order.

The options to the Map/Reduce command have changed in 1.8, causing incompatibility with previous releases. If you use MapReduce, please see Map Reduce Output Options page. If using map/reduce, this likely also means you need a recent version of your client driver.

To upgrade, shutdown the old mongod and the restart with the new binaries. See Upgrading to 1.8.x for more details.

What's New

Journaling

MongoDB now supports write-ahead journaling to facilitate fast crash recovery and durability in the storage engine. With journaling enabled, a mongod can be quickly restarted following a crash without needing to repair the collections.

Journaling Documentation

Sparse and Covered Indexes

Sparse Indexes are indexes that only include documents that contain the fields specified in the index. Documents missing the field will not appear in the index at all. This can significantly reduce index size for attributes that are contained in a subset of documents within a collection.

Covered Indexes enable queries to be answered entirely from the index when the query only requests fields that are contained in the index.

Incremental Map/Reduce Support

Map/Reduce supports new output options that enable incrementally updating existing collections. Previously, a Map/Reduce job could either output to a temporary collection a named permanent collection; which it would overwrite with new data.

You now have several options for the output of your map/reduce jobs

You can merge Map/Reduce output into an existing collection. Output from the Reduce phase will replace existing keys in the output collection if it already exists. Other keys will remain in the collection.
You can now re-reduce your output with the contents of an existing collection. Each key output by the reduce phase will be reduced with the existing document in the output collection.
You can replace the existing output collection with the new results of the Map/Reduce job (equivalent to setting a permanent output collection in previous releases)
You can compute map/reduce inline and return results to the caller without persisting the results of the job. This is similar to the temporary collections generated in previous releases, except results are limited to 8MB.

The new map/reduce options are documented here.

Additional Changes and Enhancements

1.8.1

sharding migrate fix when moving larger chunks
durability fix with background indexing
fixed mongos concurrency issue with many incoming connections

1.8.0

All changes from 1.7.x series.

1.7.6

bug fixes

1.7.5

journaling
extent allocation improvements
improved replica set connectivity for mongos
getLastError improvements for sharding

1.7.4

mongos will route SLAVE_OK queries to secondaries in replica sets
new map/reduce output options
sparse indexes

1.7.3

initial covered index support
distinct can use data from indexes when possible
map/reduce can merge or reduce results into an existing collection
mongod tracks and mongostat displays network usage
sharding stability improvements

1.7.2

$rename operator to allow renaming of attributes in a document
option to db.eval not to block
geo queries with sharding
mongostat --discover option
chunk splitting enhancements
replica sets network enhancements for servers behind a nat

1.7.1

Many sharding performance enhancements
better support for $elemMatch on primitives in embedded arrays
Query optimizer enhancements on range queries
Window service enhancements
Replica set setup improvements
$pull works on primitives in arrays

1.7.0

sharding performance improvements for heavy insert loads
slave delay support for replica sets
getLastErrorDefaults for replica sets
auto completion in the shell
spherical distance for geo search
all fixes from 1.6.1 and 1.6.2

Release Announcement Forum Pages

1.8.1 1.8.0

1.7.6 1.7.5 1.7.4 1.7.3 1.7.2 1.7.1 1.7.0