Skip to content

Rewrote and corrected how tag ranges are handled #1239

New issue

Have a question about this project? Sign up for a free GitHub account to open an issue and contact its maintainers and the community.

Sign up for GitHub

By clicking “Sign up for GitHub”, you agree to our terms of service and privacy statement. We’ll occasionally send you account related emails.

Already on GitHub? Sign in to your account

Closed
wants to merge 1 commit into from
Closed

Rewrote and corrected how tag ranges are handled #1239

Changes from all commits
Commits
Show all changes
1 commit
Select commit
File filter

Filter by extension

Filter by extension
Conversations
Failed to load comments.
Loading
Jump to
Jump to file
Failed to load files.
Loading
Diff view
Diff view
21 changes: 6 additions & 15 deletions source/core/tag-aware-sharding.txt
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -43,14 +43,11 @@ of :term:`shard key` values for a sharded collection. When migrating a
chunk, the balancer will select a destination shard based on the
configured tag ranges.

The balancer migrates chunks in tagged ranges to shards with those
tags, if tagged shards are not balanced. [#specific-tagged-migrations]_

.. note::

Because a single chunk may span different tagged shard key ranges,
the balancer may migrate chunks to tagged shards that contain
values that exceed the upper bound of the selected tag range.
Since the interval between the lower bound and the upper bound of a chunk may
span more than one tag range, the balancer only checks whether the *lower bound*
of the chunk falls within a given tag range, and ignores the upper bound of
the chunk. This ensures that there is always a single well-defined target shard
for any chunk that is about to be migrated.

.. example::

Expand All @@ -65,7 +62,7 @@ tags, if tagged shards are not balanced. [#specific-tagged-migrations]_

In this cluster, the balancer will migrate a chunk with shard key
values ranging between ``150`` and ``220`` to a shard tagged
``NYC``, since ``150`` is closer to ``200`` than ``300``.
``NYC``, since ``150`` falls within the range ``100..200``.

After configuring tags on the shards and ranges of the shard key, the
cluster may take some time to reach the proper distribution of data,
Expand All @@ -74,12 +71,6 @@ distribution of data in the cluster. Once configured, the balancer
will respect tag ranges during future :ref:`balancing rounds
<sharding-internals-balancing>`.

.. [#specific-tagged-migrations] To migrate chunks in a tagged
environment, the balancer selects a target shard with a tag range
that has an *upper* bound that is *greater than* the migrating
chunk's *lower* bound. If a shard with a matching tagged range
exists, the balancer will migrate the chunk to that shard.

.. seealso::

:doc:`/tutorial/administer-shard-tags`