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---
title: Overview
weight: 100
---
Documentation Rewrite (#982) * docs: create structure of docs overhaul This commit removes all old docs and lays out the table of contents and framework for how the new documentation will be intended to be read. * docs: add design docs back in * docs: add community documentation * docs: add LogQL docs * docs: port existing operations documentation * docs: add new placeholder file for promtail configuration docs * docs: add TOC for operations/storage * docs: add Loki API documentation * docs: port troubleshooting document * docs: add docker-driver documentation * docs: link to configuration from main docker-driver document * docs: update API for new paths * docs: fix broken links in api.md and remove json marker from examples * docs: incorporate api changes from #1009 * docs: port promtail documentation * docs: add TOC to promtail configuration reference * docs: fix promtail spelling errors * docs: add loki configuration reference * docs: add TOC to configuration * docs: add loki configuration example * docs: add Loki overview with brief explanation about each component * docs: add comparisons document * docs: add info on table manager and update storage/README.md * docs: add getting started * docs: incorporate config yaml changes from #755 * docs: fix typo in releases url for promtail * docs: add installation instructions * docs: add more configuration examples * docs: add information on fluentd client fluent-bit has been temporarily removed until the PR for it is merged. * docs: PR review feedback * docs: add architecture document * docs: add missing information from old docs * `localy` typo Co-Authored-By: Ed Welch <ed@oqqer.com> * docs: s/ran/run/g * Typo * Typo * Tyop * Typo * docs: fixed typo * docs: PR feedback * docs: @cyriltovena PR feedback * docs: add more details to promtail url config option * docs: expand promtail's pipelines document with extra detail * docs: remove reference to Stage interface in pipelines.md * docs: fixed some spelling * docs: clarify promtail configuration and scraping * docs: attempt #2 at explaining promtail's usage of machine hostname * docs: spelling fixes * docs: add reference to promtail custom metrics and fix silly typo * docs: cognizant -> aware * docs: typo * docs: typos * docs: add which components expose which API endpoints in microservices mode * docs: change ksonnet installation to tanka * docs: address most @pracucci feedback * docs: fix all spelling errors so reviewers don't have to keep finding them :) * docs: incorporate changes to API endpoints made in #1022 * docs: add missing loki metrics * docs: add missing promtail metrics * docs: @pstribrany feedback * docs: more @pracucci feedback * docs: move metrics into a table * docs: update push path references to /loki/api/v1/push * docs: add detail to further explain limitations of monolithic mode * docs: add alternative names to modes_of_operation diagram * docs: add log ordering requirement * docs: add procedure for updating docs with latest version * docs: separate out stages documentation into one document per stage * docs: list supported stores in storage documentation * docs: add info on duplicate log lines in pipelines * docs: add line_format as key feature to fluentd * docs: hopefully final commit :)
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# Overview of Loki
Grafana Loki is a set of components that can be composed into a fully featured
logging stack.
Unlike other logging systems, Loki is built around the idea of only indexing
labels for logs and leaving the original log message unindexed. This means
that Loki is cheaper to operate and can be orders of magnitude more efficient.
For a more detailed version of this same document, please read
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[Architecture](../architecture/).
Documentation Rewrite (#982) * docs: create structure of docs overhaul This commit removes all old docs and lays out the table of contents and framework for how the new documentation will be intended to be read. * docs: add design docs back in * docs: add community documentation * docs: add LogQL docs * docs: port existing operations documentation * docs: add new placeholder file for promtail configuration docs * docs: add TOC for operations/storage * docs: add Loki API documentation * docs: port troubleshooting document * docs: add docker-driver documentation * docs: link to configuration from main docker-driver document * docs: update API for new paths * docs: fix broken links in api.md and remove json marker from examples * docs: incorporate api changes from #1009 * docs: port promtail documentation * docs: add TOC to promtail configuration reference * docs: fix promtail spelling errors * docs: add loki configuration reference * docs: add TOC to configuration * docs: add loki configuration example * docs: add Loki overview with brief explanation about each component * docs: add comparisons document * docs: add info on table manager and update storage/README.md * docs: add getting started * docs: incorporate config yaml changes from #755 * docs: fix typo in releases url for promtail * docs: add installation instructions * docs: add more configuration examples * docs: add information on fluentd client fluent-bit has been temporarily removed until the PR for it is merged. * docs: PR review feedback * docs: add architecture document * docs: add missing information from old docs * `localy` typo Co-Authored-By: Ed Welch <ed@oqqer.com> * docs: s/ran/run/g * Typo * Typo * Tyop * Typo * docs: fixed typo * docs: PR feedback * docs: @cyriltovena PR feedback * docs: add more details to promtail url config option * docs: expand promtail's pipelines document with extra detail * docs: remove reference to Stage interface in pipelines.md * docs: fixed some spelling * docs: clarify promtail configuration and scraping * docs: attempt #2 at explaining promtail's usage of machine hostname * docs: spelling fixes * docs: add reference to promtail custom metrics and fix silly typo * docs: cognizant -> aware * docs: typo * docs: typos * docs: add which components expose which API endpoints in microservices mode * docs: change ksonnet installation to tanka * docs: address most @pracucci feedback * docs: fix all spelling errors so reviewers don't have to keep finding them :) * docs: incorporate changes to API endpoints made in #1022 * docs: add missing loki metrics * docs: add missing promtail metrics * docs: @pstribrany feedback * docs: more @pracucci feedback * docs: move metrics into a table * docs: update push path references to /loki/api/v1/push * docs: add detail to further explain limitations of monolithic mode * docs: add alternative names to modes_of_operation diagram * docs: add log ordering requirement * docs: add procedure for updating docs with latest version * docs: separate out stages documentation into one document per stage * docs: list supported stores in storage documentation * docs: add info on duplicate log lines in pipelines * docs: add line_format as key feature to fluentd * docs: hopefully final commit :)
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## Multi Tenancy
Loki supports multi-tenancy so that data between tenants is completely
separated. Multi-tenancy is achieved through a tenant ID (which is represented
as an alphanumeric string). When multi-tenancy mode is disabled, all requests
are internally given a tenant ID of "fake".
## Modes of Operation
Loki is optimized for both running locally (or at small scale) and for scaling
horizontally: Loki comes with a _single process mode_ that runs all of the required
microservices in one process. The single process mode is great for testing Loki
or for running it at a small scale. For horizontal scalability, the
microservices of Loki can be broken out into separate processes, allowing them
to scale independently of each other.
## Components
### Distributor
The **distributor** service is responsible for handling logs written by
Sync docs to website (#2378) * update docs location * add workflow * update docs content * update content * cleanup
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[clients](../clients/). It's essentially the "first stop" in the write
Documentation Rewrite (#982) * docs: create structure of docs overhaul This commit removes all old docs and lays out the table of contents and framework for how the new documentation will be intended to be read. * docs: add design docs back in * docs: add community documentation * docs: add LogQL docs * docs: port existing operations documentation * docs: add new placeholder file for promtail configuration docs * docs: add TOC for operations/storage * docs: add Loki API documentation * docs: port troubleshooting document * docs: add docker-driver documentation * docs: link to configuration from main docker-driver document * docs: update API for new paths * docs: fix broken links in api.md and remove json marker from examples * docs: incorporate api changes from #1009 * docs: port promtail documentation * docs: add TOC to promtail configuration reference * docs: fix promtail spelling errors * docs: add loki configuration reference * docs: add TOC to configuration * docs: add loki configuration example * docs: add Loki overview with brief explanation about each component * docs: add comparisons document * docs: add info on table manager and update storage/README.md * docs: add getting started * docs: incorporate config yaml changes from #755 * docs: fix typo in releases url for promtail * docs: add installation instructions * docs: add more configuration examples * docs: add information on fluentd client fluent-bit has been temporarily removed until the PR for it is merged. * docs: PR review feedback * docs: add architecture document * docs: add missing information from old docs * `localy` typo Co-Authored-By: Ed Welch <ed@oqqer.com> * docs: s/ran/run/g * Typo * Typo * Tyop * Typo * docs: fixed typo * docs: PR feedback * docs: @cyriltovena PR feedback * docs: add more details to promtail url config option * docs: expand promtail's pipelines document with extra detail * docs: remove reference to Stage interface in pipelines.md * docs: fixed some spelling * docs: clarify promtail configuration and scraping * docs: attempt #2 at explaining promtail's usage of machine hostname * docs: spelling fixes * docs: add reference to promtail custom metrics and fix silly typo * docs: cognizant -> aware * docs: typo * docs: typos * docs: add which components expose which API endpoints in microservices mode * docs: change ksonnet installation to tanka * docs: address most @pracucci feedback * docs: fix all spelling errors so reviewers don't have to keep finding them :) * docs: incorporate changes to API endpoints made in #1022 * docs: add missing loki metrics * docs: add missing promtail metrics * docs: @pstribrany feedback * docs: more @pracucci feedback * docs: move metrics into a table * docs: update push path references to /loki/api/v1/push * docs: add detail to further explain limitations of monolithic mode * docs: add alternative names to modes_of_operation diagram * docs: add log ordering requirement * docs: add procedure for updating docs with latest version * docs: separate out stages documentation into one document per stage * docs: list supported stores in storage documentation * docs: add info on duplicate log lines in pipelines * docs: add line_format as key feature to fluentd * docs: hopefully final commit :)
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path for log data. Once the distributor receives log data, it splits them into
batches and sends them to multiple [ingesters](#ingester) in parallel.
Distributors communicate with ingesters via [gRPC](https://grpc.io). They are
stateless and can be scaled up and down as needed.
#### Hashing
Distributors use consistent hashing in conjunction with a configurable
replication factor to determine which instances of the ingester service should
receive log data.
The hash is based on a combination of the log's labels and the tenant ID.
A hash ring stored in [Consul](https://www.consul.io) is used to achieve
consistent hashing; all [ingesters](#ingester) register themselves into the
hash ring with a set of tokens they own. Distributors then find the token that
most closely matches the value of the log's hash and will send data to that
token's owner.
#### Quorum consistency
Since all distributors share access to the same hash ring, write requests can be
sent to any distributor.
To ensure consistent query results, Loki uses
[Dynamo-style](https://www.allthingsdistributed.com/files/amazon-dynamo-sosp2007.pdf)
quorum consistency on reads and writes. This means that the distributor will wait
for a positive response of at least one half plus one of the ingesters to send
the sample to before responding to the user.
### Ingester
The **ingester** service is responsible for writing log data to long-term
storage backends (DynamoDB, S3, Cassandra, etc.).
docs: Document timestamp ordering rules (#1521) Co-authored-by: Ed Welch <ed@oqqer.com>
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The ingester validates that ingested log lines are not out of order. When an
ingester receives a log line that doesn't follow the expected order, the line
is rejected and an error is returned to the user. See the section on [Timestamp
ordering](#timestamp-ordering) for more information.
Documentation Rewrite (#982) * docs: create structure of docs overhaul This commit removes all old docs and lays out the table of contents and framework for how the new documentation will be intended to be read. * docs: add design docs back in * docs: add community documentation * docs: add LogQL docs * docs: port existing operations documentation * docs: add new placeholder file for promtail configuration docs * docs: add TOC for operations/storage * docs: add Loki API documentation * docs: port troubleshooting document * docs: add docker-driver documentation * docs: link to configuration from main docker-driver document * docs: update API for new paths * docs: fix broken links in api.md and remove json marker from examples * docs: incorporate api changes from #1009 * docs: port promtail documentation * docs: add TOC to promtail configuration reference * docs: fix promtail spelling errors * docs: add loki configuration reference * docs: add TOC to configuration * docs: add loki configuration example * docs: add Loki overview with brief explanation about each component * docs: add comparisons document * docs: add info on table manager and update storage/README.md * docs: add getting started * docs: incorporate config yaml changes from #755 * docs: fix typo in releases url for promtail * docs: add installation instructions * docs: add more configuration examples * docs: add information on fluentd client fluent-bit has been temporarily removed until the PR for it is merged. * docs: PR review feedback * docs: add architecture document * docs: add missing information from old docs * `localy` typo Co-Authored-By: Ed Welch <ed@oqqer.com> * docs: s/ran/run/g * Typo * Typo * Tyop * Typo * docs: fixed typo * docs: PR feedback * docs: @cyriltovena PR feedback * docs: add more details to promtail url config option * docs: expand promtail's pipelines document with extra detail * docs: remove reference to Stage interface in pipelines.md * docs: fixed some spelling * docs: clarify promtail configuration and scraping * docs: attempt #2 at explaining promtail's usage of machine hostname * docs: spelling fixes * docs: add reference to promtail custom metrics and fix silly typo * docs: cognizant -> aware * docs: typo * docs: typos * docs: add which components expose which API endpoints in microservices mode * docs: change ksonnet installation to tanka * docs: address most @pracucci feedback * docs: fix all spelling errors so reviewers don't have to keep finding them :) * docs: incorporate changes to API endpoints made in #1022 * docs: add missing loki metrics * docs: add missing promtail metrics * docs: @pstribrany feedback * docs: more @pracucci feedback * docs: move metrics into a table * docs: update push path references to /loki/api/v1/push * docs: add detail to further explain limitations of monolithic mode * docs: add alternative names to modes_of_operation diagram * docs: add log ordering requirement * docs: add procedure for updating docs with latest version * docs: separate out stages documentation into one document per stage * docs: list supported stores in storage documentation * docs: add info on duplicate log lines in pipelines * docs: add line_format as key feature to fluentd * docs: hopefully final commit :)
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The ingester validates that ingested log lines are received in
timestamp-ascending order (i.e., each log has a timestamp that occurs at a later
time than the log before it). When the ingester receives a log that does not
follow this order, the log line is rejected and an error is returned.
Logs from each unique set of labels are built up into "chunks" in memory and
then flushed to the backing storage backend.
If an ingester process crashes or exits abruptly, all the data that has not yet
been flushed will be lost. Loki is usually configured to replicate multiple
replicas (usually 3) of each log to mitigate this risk.
docs: Document timestamp ordering rules (#1521) Co-authored-by: Ed Welch <ed@oqqer.com>
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#### Timestamp Ordering
In general, all lines pushed to Loki for a given stream (unique combination of
labels) must have a newer timestamp than the line received before it. There are,
however, two cases for handling logs for the same stream with identical
nanosecond timestamps:
1. If the incoming line exactly matches the previously received line (matching
both the previous timestamp and log text), the incoming line will be treated
as an exact duplicate and ignored.
2. If the incoming line has the same timestamp as the previous line but
different content, the log line is accepted. This means it is possible to
have two different log lines for the same timestamp.
Documentation Rewrite (#982) * docs: create structure of docs overhaul This commit removes all old docs and lays out the table of contents and framework for how the new documentation will be intended to be read. * docs: add design docs back in * docs: add community documentation * docs: add LogQL docs * docs: port existing operations documentation * docs: add new placeholder file for promtail configuration docs * docs: add TOC for operations/storage * docs: add Loki API documentation * docs: port troubleshooting document * docs: add docker-driver documentation * docs: link to configuration from main docker-driver document * docs: update API for new paths * docs: fix broken links in api.md and remove json marker from examples * docs: incorporate api changes from #1009 * docs: port promtail documentation * docs: add TOC to promtail configuration reference * docs: fix promtail spelling errors * docs: add loki configuration reference * docs: add TOC to configuration * docs: add loki configuration example * docs: add Loki overview with brief explanation about each component * docs: add comparisons document * docs: add info on table manager and update storage/README.md * docs: add getting started * docs: incorporate config yaml changes from #755 * docs: fix typo in releases url for promtail * docs: add installation instructions * docs: add more configuration examples * docs: add information on fluentd client fluent-bit has been temporarily removed until the PR for it is merged. * docs: PR review feedback * docs: add architecture document * docs: add missing information from old docs * `localy` typo Co-Authored-By: Ed Welch <ed@oqqer.com> * docs: s/ran/run/g * Typo * Typo * Tyop * Typo * docs: fixed typo * docs: PR feedback * docs: @cyriltovena PR feedback * docs: add more details to promtail url config option * docs: expand promtail's pipelines document with extra detail * docs: remove reference to Stage interface in pipelines.md * docs: fixed some spelling * docs: clarify promtail configuration and scraping * docs: attempt #2 at explaining promtail's usage of machine hostname * docs: spelling fixes * docs: add reference to promtail custom metrics and fix silly typo * docs: cognizant -> aware * docs: typo * docs: typos * docs: add which components expose which API endpoints in microservices mode * docs: change ksonnet installation to tanka * docs: address most @pracucci feedback * docs: fix all spelling errors so reviewers don't have to keep finding them :) * docs: incorporate changes to API endpoints made in #1022 * docs: add missing loki metrics * docs: add missing promtail metrics * docs: @pstribrany feedback * docs: more @pracucci feedback * docs: move metrics into a table * docs: update push path references to /loki/api/v1/push * docs: add detail to further explain limitations of monolithic mode * docs: add alternative names to modes_of_operation diagram * docs: add log ordering requirement * docs: add procedure for updating docs with latest version * docs: separate out stages documentation into one document per stage * docs: list supported stores in storage documentation * docs: add info on duplicate log lines in pipelines * docs: add line_format as key feature to fluentd * docs: hopefully final commit :)
6 years ago
#### Handoff
By default, when an ingester is shutting down and tries to leave the hash ring,
it will wait to see if a new ingester tries to enter before flushing and will
try to initiate a handoff. The handoff will transfer all of the tokens and
in-memory chunks owned by the leaving ingester to the new ingester.
This process is used to avoid flushing all chunks when shutting down, which is a
slow process.
#### Filesystem Support
While ingesters do support writing to the filesystem through BoltDB, this only
works in single-process mode as [queriers](#querier) need access to the same
back-end store and BoltDB only allows one process to have a lock on the DB at a
given time.
### Querier
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The **querier** service handles the actual [LogQL](../logql/) evaluation of
Documentation Rewrite (#982) * docs: create structure of docs overhaul This commit removes all old docs and lays out the table of contents and framework for how the new documentation will be intended to be read. * docs: add design docs back in * docs: add community documentation * docs: add LogQL docs * docs: port existing operations documentation * docs: add new placeholder file for promtail configuration docs * docs: add TOC for operations/storage * docs: add Loki API documentation * docs: port troubleshooting document * docs: add docker-driver documentation * docs: link to configuration from main docker-driver document * docs: update API for new paths * docs: fix broken links in api.md and remove json marker from examples * docs: incorporate api changes from #1009 * docs: port promtail documentation * docs: add TOC to promtail configuration reference * docs: fix promtail spelling errors * docs: add loki configuration reference * docs: add TOC to configuration * docs: add loki configuration example * docs: add Loki overview with brief explanation about each component * docs: add comparisons document * docs: add info on table manager and update storage/README.md * docs: add getting started * docs: incorporate config yaml changes from #755 * docs: fix typo in releases url for promtail * docs: add installation instructions * docs: add more configuration examples * docs: add information on fluentd client fluent-bit has been temporarily removed until the PR for it is merged. * docs: PR review feedback * docs: add architecture document * docs: add missing information from old docs * `localy` typo Co-Authored-By: Ed Welch <ed@oqqer.com> * docs: s/ran/run/g * Typo * Typo * Tyop * Typo * docs: fixed typo * docs: PR feedback * docs: @cyriltovena PR feedback * docs: add more details to promtail url config option * docs: expand promtail's pipelines document with extra detail * docs: remove reference to Stage interface in pipelines.md * docs: fixed some spelling * docs: clarify promtail configuration and scraping * docs: attempt #2 at explaining promtail's usage of machine hostname * docs: spelling fixes * docs: add reference to promtail custom metrics and fix silly typo * docs: cognizant -> aware * docs: typo * docs: typos * docs: add which components expose which API endpoints in microservices mode * docs: change ksonnet installation to tanka * docs: address most @pracucci feedback * docs: fix all spelling errors so reviewers don't have to keep finding them :) * docs: incorporate changes to API endpoints made in #1022 * docs: add missing loki metrics * docs: add missing promtail metrics * docs: @pstribrany feedback * docs: more @pracucci feedback * docs: move metrics into a table * docs: update push path references to /loki/api/v1/push * docs: add detail to further explain limitations of monolithic mode * docs: add alternative names to modes_of_operation diagram * docs: add log ordering requirement * docs: add procedure for updating docs with latest version * docs: separate out stages documentation into one document per stage * docs: list supported stores in storage documentation * docs: add info on duplicate log lines in pipelines * docs: add line_format as key feature to fluentd * docs: hopefully final commit :)
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logs stored in long-term storage.
It first tries to query all ingesters for in-memory data before falling back to
loading data from the backend store.
loki frontend docs additions (#1611) * loki frontend docs additions * s/cortex/loki/ Co-Authored-By: Cyril Tovena <cyril.tovena@gmail.com> * Update docs/configuration/query-frontend.md Co-Authored-By: Cyril Tovena <cyril.tovena@gmail.com> * addresses pr comments * query frontend docs downstream via http, use 9091 as http port * removes grpc references in frontend yaml snippet * more comprehensive query frontend example description * makes query frontend example deployable alongside existing loki Co-authored-by: Cyril Tovena <cyril.tovena@gmail.com>
6 years ago
### Query frontend
The **query-frotend** service is an optional component in front of a pool of queriers. It's responsible for fairly scheduling requests between them, paralleling them when possible, and caching.
Documentation Rewrite (#982) * docs: create structure of docs overhaul This commit removes all old docs and lays out the table of contents and framework for how the new documentation will be intended to be read. * docs: add design docs back in * docs: add community documentation * docs: add LogQL docs * docs: port existing operations documentation * docs: add new placeholder file for promtail configuration docs * docs: add TOC for operations/storage * docs: add Loki API documentation * docs: port troubleshooting document * docs: add docker-driver documentation * docs: link to configuration from main docker-driver document * docs: update API for new paths * docs: fix broken links in api.md and remove json marker from examples * docs: incorporate api changes from #1009 * docs: port promtail documentation * docs: add TOC to promtail configuration reference * docs: fix promtail spelling errors * docs: add loki configuration reference * docs: add TOC to configuration * docs: add loki configuration example * docs: add Loki overview with brief explanation about each component * docs: add comparisons document * docs: add info on table manager and update storage/README.md * docs: add getting started * docs: incorporate config yaml changes from #755 * docs: fix typo in releases url for promtail * docs: add installation instructions * docs: add more configuration examples * docs: add information on fluentd client fluent-bit has been temporarily removed until the PR for it is merged. * docs: PR review feedback * docs: add architecture document * docs: add missing information from old docs * `localy` typo Co-Authored-By: Ed Welch <ed@oqqer.com> * docs: s/ran/run/g * Typo * Typo * Tyop * Typo * docs: fixed typo * docs: PR feedback * docs: @cyriltovena PR feedback * docs: add more details to promtail url config option * docs: expand promtail's pipelines document with extra detail * docs: remove reference to Stage interface in pipelines.md * docs: fixed some spelling * docs: clarify promtail configuration and scraping * docs: attempt #2 at explaining promtail's usage of machine hostname * docs: spelling fixes * docs: add reference to promtail custom metrics and fix silly typo * docs: cognizant -> aware * docs: typo * docs: typos * docs: add which components expose which API endpoints in microservices mode * docs: change ksonnet installation to tanka * docs: address most @pracucci feedback * docs: fix all spelling errors so reviewers don't have to keep finding them :) * docs: incorporate changes to API endpoints made in #1022 * docs: add missing loki metrics * docs: add missing promtail metrics * docs: @pstribrany feedback * docs: more @pracucci feedback * docs: move metrics into a table * docs: update push path references to /loki/api/v1/push * docs: add detail to further explain limitations of monolithic mode * docs: add alternative names to modes_of_operation diagram * docs: add log ordering requirement * docs: add procedure for updating docs with latest version * docs: separate out stages documentation into one document per stage * docs: list supported stores in storage documentation * docs: add info on duplicate log lines in pipelines * docs: add line_format as key feature to fluentd * docs: hopefully final commit :)
6 years ago
## Chunk Store
The **chunk store** is Loki's long-term data store, designed to support
interactive querying and sustained writing without the need for background
maintenance tasks. It consists of:
* An index for the chunks. This index can be backed by
[DynamoDB from Amazon Web Services](https://aws.amazon.com/dynamodb),
[Bigtable from Google Cloud Platform](https://cloud.google.com/bigtable), or
[Apache Cassandra](https://cassandra.apache.org).
* A key-value (KV) store for the chunk data itself, which can be DynamoDB,
Bigtable, Cassandra again, or an object store such as
[Amazon * S3](https://aws.amazon.com/s3)
> Unlike the other core components of Loki, the chunk store is not a separate
> service, job, or process, but rather a library embedded in the two services
> that need to access Loki data: the [ingester](#ingester) and [querier](#querier).
The chunk store relies on a unified interface to the
"[NoSQL](https://en.wikipedia.org/wiki/NoSQL)" stores (DynamoDB, Bigtable, and
Cassandra) that can be used to back the chunk store index. This interface
assumes that the index is a collection of entries keyed by:
* A **hash key**. This is required for *all* reads and writes.
* A **range key**. This is required for writes and can be omitted for reads,
which can be queried by prefix or range.
The interface works somewhat differently across the supported databases:
* DynamoDB supports range and hash keys natively. Index entries are thus
modelled directly as DynamoDB entries, with the hash key as the distribution
key and the range as the range key.
* For Bigtable and Cassandra, index entries are modelled as individual column
values. The hash key becomes the row key and the range key becomes the column
key.
A set of schemas are used to map the matchers and label sets used on reads and
writes to the chunk store into appropriate operations on the index. Schemas have
been added as Loki has evolved, mainly in an attempt to better load balance
writes and improve query performance.