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HBASE-26265 Update ref guide to mention the new store file tracker im… #3942
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[[storefiletracking]] | ||||||||
= Store File Tracking | ||||||||
:doctype: book | ||||||||
:numbered: | ||||||||
:toc: left | ||||||||
:icons: font | ||||||||
:experimental: | ||||||||
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== Overview | ||||||||
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This feature introduces an abstraction layer to track store files still used/needed by store | ||||||||
engines, allowing for plugging different approaches of identifying store | ||||||||
files required by the given store. | ||||||||
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Historically, HBase internals have relied on creating hfiles on temporary directories first, renaming | ||||||||
those files to the actual store directory at operation commit time. That's a simple and convenient | ||||||||
way to separate transient from already finalised files that are ready to serve client reads with data. | ||||||||
This approach works well with strong consistent file systems, but with the popularity of less consistent | ||||||||
file systems, mainly Object Store file systems, dependency on rename operations starts to introduce | ||||||||
performance penalties. Amazon S3 Object Store, in particular, has been the most affected deployment, | ||||||||
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due to the its lack of atomic renames, requiring an additional locking layer implemented by HBOSS, | ||||||||
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to guarantee consistency and integrity of operations. | ||||||||
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Maybe I'm being nit-picky here? I think it makes a confusing topic easier to understand if we just say "atomic renames", even though "consistency" and "integrity" would be things sacrificed when we have non-atomic renames :) |
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With *Store File Tracking*, decision on where to originally create new hfiles and how to proceed upon | ||||||||
commit is delegated to the specific Store File Tracking implementation. | ||||||||
It can be set at individual Table or Column Family configurations, as well as in processes | ||||||||
*hbase-site.xml* configuration file. | ||||||||
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NOTE: When specified in *hbase_site.xml*, this configuration is also saved into tables configuration | ||||||||
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at table creation time. This is to avoid dangerous configuration mismatches between processes, which | ||||||||
could potentially lead to data loss. | ||||||||
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== Available Implementations | ||||||||
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Store File Tracking initial version provides three builtin implementations: | ||||||||
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* DEFAULT | ||||||||
* FILE | ||||||||
* MIGRATION | ||||||||
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### DEFAULT | ||||||||
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As per the name, this is the Store File Tracking implementation used by default when now explicit | ||||||||
configuration has been defined. The DEFAULT tracker implements the standard approach using temporary | ||||||||
directories and renames. | ||||||||
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### FILE | ||||||||
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A file tracker implementation that creates new files straight in the store directory, avoiding the | ||||||||
need for rename operations. It keeps a list of committed hfiles in memory, backed by meta files, in | ||||||||
each store directory. Whenever a new hfile is committed, the list of _tracked files_ in the given | ||||||||
store is updated and a new meta file is written with this list contents, discarding the previous | ||||||||
meta file now containing an out dated list. | ||||||||
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### MIGRATION | ||||||||
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A special implementation to be used when swapping between Store File Tracking implementations on | ||||||||
pre-existing tables that already contain data, and therefore, files being tracked under an specific | ||||||||
logic. | ||||||||
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== Usage | ||||||||
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For fresh deployments that don't yet contain any user data, *FILE* implementation can be just set as | ||||||||
value for *hbase.store.file-tracker.impl* property in global *hbase-site.xml* configuration, prior | ||||||||
to the first hbase start. Omitting this property sets the *DEFAULT* implementation. | ||||||||
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### Switching implementations globally | ||||||||
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For running clusters with tables already containing data, Store File Tracking implementation can | ||||||||
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only be changed with the *MIGRATION* implementation, so that the _new tracker_ can safely build its | ||||||||
list of tracked files based on the list of the _current tracker_. Additional to the | ||||||||
*hbase.store.file-tracker.impl* property, *MIGRATION* requires the | ||||||||
*hbase.store.file-tracker.migration.src.impl* and *hbase.store.file-tracker.migration.dst.impl*, | ||||||||
where the _current_ and _new_ tracker should be specified. For example, to set *MIGRATION* from | ||||||||
*DEFAULT* to *FILE*, the following should be set in the global config: | ||||||||
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---- | ||||||||
<property> | ||||||||
<name>hbase.store.file-tracker.impl</name> | ||||||||
<value>MIGRATION</value> | ||||||||
</property> | ||||||||
<property> | ||||||||
<name>hbase.store.file-tracker.migration.src.impl</name> | ||||||||
<value>DEFAULT</value> | ||||||||
</property> | ||||||||
<property> | ||||||||
<name>hbase.store.file-tracker.migration.dst.impl</name> | ||||||||
<value>FILE</value> | ||||||||
</property> | ||||||||
---- | ||||||||
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A cluster restart would be needed to effectivelly apply the above configuration. | ||||||||
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NOTE: When MIGRATION is defined globally, new tables creation is not allowed. | ||||||||
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Once cluster has completely started and all regions have already become online, *MIGRATION* tracker | ||||||||
can be disabled and the _new_ implementation should be the one set in *hbase.store.file-tracker.impl*. | ||||||||
On the above example, the new configuration would be: | ||||||||
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---- | ||||||||
<property> | ||||||||
<name>hbase.store.file-tracker.impl</name> | ||||||||
<value>FILE</value> | ||||||||
</property> | ||||||||
---- | ||||||||
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Restart the cluster again to complete migration and allow new tables creation to be executed again. | ||||||||
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### Configuring for Table or Column Family | ||||||||
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The previous example conveniently allows to set Store File Tracker desired configuration on a single | ||||||||
place for all cluster tables. That may not be always desired, either because clusters restarts can be | ||||||||
discouraging, or maybe because some user domain might be more critical to experiment a new feature. | ||||||||
Whatever the reason, Store File Tracking can be set at Table or Column Family level configuration. | ||||||||
For example, to specify *FILE* implementation in the table configuration at table creation time, | ||||||||
the following should be applied: | ||||||||
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---- | ||||||||
create 'my-table', 'f1', 'f2', {CONFIGURATION => {'hbase.store.file-tracker.impl' => 'FILE'}} | ||||||||
---- | ||||||||
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To define *FILE* for an specific Column Family: | ||||||||
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---- | ||||||||
create 'my-table', {NAME=> '1', CONFIGURATION => {'hbase.store.file-tracker.impl' => 'FILE'}} | ||||||||
---- | ||||||||
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### Switching trackers at Table or Column Family | ||||||||
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Similarly to when switching implementations at global configuration, when switching _trackers_ for | ||||||||
individual tables or column families, the *MIGRATION* tracker is also required. For example, to | ||||||||
switch _tracker_ from *DEFAULT* to *FILE* in a table configuration: | ||||||||
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---- | ||||||||
alter 'my-table', CONFIGURATION => {'hbase.store.file-tracker.impl' => 'MIGRATION', | ||||||||
'hbase.store.file-tracker.migration.src.impl' => 'DEFAULT', | ||||||||
'hbase.store.file-tracker.migration.dst.impl' => 'FILE'} | ||||||||
---- | ||||||||
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To apply similar switch at column family level configuration: | ||||||||
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---- | ||||||||
alter 'my-table', {NAME => 'f1', CONFIGURATION => {'hbase.store.file-tracker.impl' => 'MIGRATION', | ||||||||
'hbase.store.file-tracker.migration.src.impl' => 'DEFAULT', | ||||||||
'hbase.store.file-tracker.migration.dst.impl' => 'FILE'}} | ||||||||
---- | ||||||||
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Once all table regions have been onlined again, don't forget to disable MIGRATION, by now setting | ||||||||
*hbase.store.file-tracker.migration.dst.impl* value as the *hbase.store.file-tracker.impl*. In the above | ||||||||
example, that would be as follows: | ||||||||
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---- | ||||||||
alter 'my-table', CONFIGURATION => {'hbase.store.file-tracker.impl' => 'FILE'} | ||||||||
---- |
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