This page describes changes and new features introduced in MongoDB Mongosync 1.17.
1.17.0 Release
October 1, 2025
New Features
Metrics Information
Starting in version 1.17, mongosync logs metrics that contain information
about the host's CPU and memory usage as percentages of the total available
CPU and memory. It also logs this information at the debug level.
/progress Network Information
mongosync 1.17 adds the source.pingLatencyMs and destination.pingLatencyMs
fields to the /progress endpoint response.
Automatic Balancer Disabling
Starting in version 1.17, mongosync disables the balancer on source
and destination clusters during initialization if it detects that the
balancers are not disabled.
This only applies during initialization. If mongosync detects that
either balancer is enabled after the migration begins, mongosync fails.
After disabling the balancer, mongosync waits for 15 minutes to ensure that
in-progress chunk migrations complete before continuing with the migration.
If the migration is not reversible and mongosync disables the source or destination
balancer during initialization, after a successful commit mongosync re-enables
the balancer(s) it disabled. If the migration is reversible, mongosync does not re-enable
any balancers to avoid making users wait 15 minutes.
IMPORTANT: If mongosync disables the balancer for either cluster
and then fails before commit, you must re-enable the balancer(s) manually
by using the balancerStart database command if you do not plan
to run mongosync again.
Performance Improvements
Build Indexes After Collection Copy
mongosync 1.17 builds indexes after collection copy by default, which results
in a faster migration for indexed databases. For more information, see the
/start endpoint request parameters.
Fixed Issues
mongosynccreates 90 chunks per destination shard by default instead of 2 chunks.Fixes a bug where the embedded verifier might incorrectly compute internal IDs for sharded collections with shard keys that include multiple periods (
.).Removes the embedded verifier's 6-hour timeout for initial hashing. This reduces timeout errors for large collections or slow clusters.
Fixes a rare bug where the verifier did not correctly process a collection rename event if using namespace filtering, leading to repeated failures that prevented the commit process from completing.
Other Changes
mongosyncnow compresses log files when it rotates them. Starting in version 1.17, all files besides the current log file are compressed usinggzip.mongosyncfails if there is a balancing window configured on the source or destination cluster.Release artifacts, such as tarballs and zipfiles, now include a file with a SARIF report in JSON format. This report contains the results of the static analysis tool that
mongosyncruns to look for security issues.mongosyncchecks for incorrect writes to the source cluster during commit. If any writes to the source cluster are detected, the migration fails.The embedded verifier enables network compression by default.
The /progress endpoint now reports
canCommit: falseuntil the verifier is in an appropriate state for commit.
Live Upgrades
Live upgrades to 1.17 are not supported.
Minimum Supported Version
For information on minimum supported versions, see MongoDB Server Version Compatibility.
For best performance, upgrade your source and destination clusters to the most recent MongoDB Server patch release prior to migration. For more information, see Upgrade to the Latest Self-Managed Patch Release of MongoDB.