Updates the supported upgrade path table in [Upgrade Elasticsearch][0]
to include a new row for maintenance releases. For example, this row
covers upgrading from 7.6.0 to 7.6.2.
The new table row only displays for releases greater than n.x.0. For
example, the new row will display for the 7.7.1 release but not the
7.7.0 release.
[0]: https://www.elastic.co/guide/en/elasticsearch/reference/master/setup-upgrade.html
Provides basic repository-level stats that will allow us to get some insight into how many
requests are actually being made by the underlying SDK. Currently only tracks GET and LIST
calls for S3 repositories. Most of the code is unfortunately boiler plate to add a new endpoint
that will help us better understand some of the low-level dynamics of searchable snapshots.
With this change, when a task is canceled, the task manager will cancel
not only its direct child tasks but all also its descendant tasks.
Closes#50990
Adds support for filters to T-Test aggregation. The filters can be used to
select populations based on some criteria and use values from the same or
different fields.
Closes#53692
The secure_settings_password was never taken into consideration in
the ReloadSecureSettings API. This commit fixes that and adds
necessary REST layer testing. Doing so, it also:
- Allows TestClusters to have a password protected keystore
so that it can be set for tests.
- Adds a parameter to the run task so that elastisearch can
be run with a password protected keystore from source.
The usage of local parameter for GetFieldMappingRequest has been removed from the underlying transport action since v2.0.
This PR deprecates the parameter from rest layer. It will be removed in next major version.
Changes boilerplate sentence of "If using a field as the argument, this
parameter only supports..." to "...this parameter supports only...".
The latter is a bit more clear and readable.
Some of these characters are special to Asciidoctor and they ruin the
rendering on this page. Instead, we use a macro to passthrough these
characters without Asciidoctor applying any subtitutions to them. This
commit then addresses some rendering issues in the thread pool docs.
Co-authored-by: James Rodewig <james.rodewig@elastic.co>
We found some problems during the test.
Data: 200Million docs, 1 shard, 0 replica
hits | avg | sum | value_count |
----------- | ------- | ------- | ----------- |
20,000 | .038s | .033s | .063s |
200,000 | .127s | .125s | .334s |
2,000,000 | .789s | .729s | 3.176s |
20,000,000 | 4.200s | 3.239s | 22.787s |
200,000,000 | 21.000s | 22.000s | 154.917s |
The performance of `avg`, `sum` and other is very close when performing
statistics, but the performance of `value_count` has always been poor,
even not on an order of magnitude. Based on some common-sense knowledge,
we think that `value_count` and sum are similar operations, and the time
consumed should be the same. Therefore, we have discussed the agg
of `value_count`.
The principle of counting in es is to traverse the field of each
document. If the field is an ordinary value, the count value is
increased by 1. If it is an array type, the count value is increased
by n. However, the problem lies in traversing each document and taking
out the field, which changes from disk to an object in the Java
language. We summarize its current problems with Elasticsearch as:
- Number cast to string overhead, and GC problems caused by a large
number of strings
- After the number type is converted to string, sorting and other
unnecessary operations are performed
Here is the proof of type conversion overhead.
```
// Java long to string source code, getChars is very time-consuming.
public static String toString(long i) {
int size = stringSize(i);
if (COMPACT_STRINGS) {
byte[] buf = new byte[size];
getChars(i, size, buf);
return new String(buf, LATIN1);
} else {
byte[] buf = new byte[size * 2];
StringUTF16.getChars(i, size, buf);
return new String(buf, UTF16);
}
}
```
test type | average | min | max | sum
------------ | ------- | ---- | ----------- | -------
double->long | 32.2ns | 28ns | 0.024ms | 3.22s
long->double | 31.9ns | 28ns | 0.036ms | 3.19s
long->String | 163.8ns | 93ns | 1921 ms | 16.3s
particularly serious.
Our optimization code is actually very simple. It is to manage different
types separately, instead of uniformly converting to string unified
processing. We added type identification in ValueCountAggregator, and
made special treatment for number and geopoint types to cancel their
type conversion. Because the string type is reduced and the string
constant is reduced, the improvement effect is very obvious.
hits | avg | sum | value_count | value_count | value_count | value_count | value_count | value_count |
| | | double | double | keyword | keyword | geo_point | geo_point |
| | | before | after | before | after | before | after |
----------- | ------- | ------- | ----------- | ----------- | ----------- | ----------- | ----------- | ----------- |
20,000 | 38s | .033s | .063s | .026s | .030s | .030s | .038s | .015s |
200,000 | 127s | .125s | .334s | .078s | .116s | .099s | .278s | .031s |
2,000,000 | 789s | .729s | 3.176s | .439s | .348s | .386s | 3.365s | .178s |
20,000,000 | 4.200s | 3.239s | 22.787s | 2.700s | 2.500s | 2.600s | 25.192s | 1.278s |
200,000,000 | 21.000s | 22.000s | 154.917s | 18.990s | 19.000s | 20.000s | 168.971s | 9.093s |
- The results are more in line with common sense. `value_count` is about
the same as `avg`, `sum`, etc., or even lower than these. Previously,
`value_count` was much larger than avg and sum, and it was not even an
order of magnitude when the amount of data was large.
- When calculating numeric types such as `double` and `long`, the
performance is improved by about 8 to 9 times; when calculating the
`geo_point` type, the performance is improved by 18 to 20 times.
The use of available processors, the terminology, and the settings
around it have evolved over time. This commit cleans up some places in
the codes and in the docs to adjust to the current terminology.
Creates a reusable template for token filter reference documentation.
Contributors can make a copy of this template and customize it when
documenting new token filters.
Implement DATETIME_PARSE(<datetime_str>, <pattern_str>) function
which allows to parse a datetime string according to the specified
pattern into a datetime object. The patterns allowed are those of
java.time.format.DateTimeFormatter.
Relates to #53714
(cherry picked from commit 3febcd8f3cdf9fdda4faf01f23a5f139f38b57e0)
Implement DATETIME_FORMAT(<date/datetime/time>, ) function
which allows for formatting a timestamp to the specified format. The
patterns allowed as those of java.time.format.DateTimeFormatter.
Related to #53714
(cherry picked from commit 72be0b54a9299e87e785469cdc9aafac2a48c046)
In 7.x, an index template will fail to apply if it contains a `_default_`
mapping. Several users have expressed confusion over the fact that loading the
template doesn't show any default mappings. This docs change clarifies that in
order to see all mappings in the template, you must pass `include_type_name`.
Adds a detailed example to the "Avoid scripts" section of the "Tune
for search speed" docs. The detail outlines how a script used to
transform indexed data can be moved to ingest.
The update also removes an outdated reference to supported script
languages.
This commit adds a new point field that is able to index arbitrary pair of values (x/y)
in the cartesian space. It only supports filtering using shape queries at the moment.
This is a backport of #54803 for 7.x.
This pull request cherry picks the squashed commit from #54803 with the additional commits:
6f50c92 which adjusts master code to 7.x
a114549 to mute a failing ILM test (#54818)
48cbca1 and 50186b2 that cleans up and fixes the previous test
aae12bb that adds a missing feature flag (#54861)
6f330e3 that adds missing serialization bits (#54864)
bf72c02 that adjust the version in YAML tests
a51955f that adds some plumbing for the transport client used in integration tests
Co-authored-by: David Turner <david.turner@elastic.co>
Co-authored-by: Yannick Welsch <yannick@welsch.lu>
Co-authored-by: Lee Hinman <dakrone@users.noreply.github.com>
Co-authored-by: Andrei Dan <andrei.dan@elastic.co>
Adds t_test metric aggregation that can perform paired and unpaired two-sample
t-tests. In this PR support for filters in unpaired is still missing. It will
be added in a follow-up PR.
Relates to #53692
Today when canceling a task we broadcast ban/unban requests to all nodes
in the cluster. This strategy does not scale well for hierarchical
cancellation. With this change, we will track outstanding child requests
and broadcast the cancellation to only nodes that have outstanding child
tasks. This change also prevents a parent task from sending child
requests once it got canceled.
Relates #50990
Supersedes #51157
Co-authored-by: Igor Motov <igor@motovs.org>
Co-authored-by: Yannick Welsch <yannick@welsch.lu>
Looking into #50237 I realized that two of the examples given in the
documentation around date math rounding for range queries on date fields using
`gt` and `lt` is slightly off by a nanosecond. This PR changes this to the
bounds that are currently parsed using these parameters.
* Document VarcharLimit and EarlyExecution params
Add the documentation for the newly added VarcharLimit and
EarlyExecution DSN attributes.
* Remove obsolete VersionChecking param
This param had been removed already along the #53082 work.
* Update docs/reference/sql/endpoints/odbc/configuration.asciidoc
fix typo
Co-Authored-By: Stuart Cam <stuart@codebrain.co.uk>
* Update docs/reference/sql/endpoints/odbc/configuration.asciidoc
fix typo
Co-Authored-By: Stuart Cam <stuart@codebrain.co.uk>
(cherry picked from commit f38761631a12b38f7f075635f7ac61dc96656cd7)
In #33933 we disallowed changing the `enabled` parameter in object mappings.
However, the fix didn't cover the root object mapper. This PR adjusts the change
to also include the root mapper and clarifies the error message.
The `indices.recovery.max_bytes_per_sec` recovery bandwidth limit can differ
between nodes if it is not set dynamically, but today this is not obvious. This
commit adds a paragraph to its documentation clarifying how to set different
bandwidth limits on each node.
Co-Authored-By: James Rodewig <james.rodewig@elastic.co>
* [ML] add new inference_config field to trained model config (#54421)
A new field called `inference_config` is now added to the trained model config object. This new field allows for default inference settings from analytics or some external model builder.
The inference processor can still override whatever is set as the default in the trained model config.
* fixing for backport
* [ML] prefer secondary authorization header for data[feed|frame] authz (#54121)
Secondary authorization headers are to be used to facilitate Kibana spaces support + ML jobs/datafeeds.
Now on PUT/Update/Preview datafeed, and PUT data frame analytics the secondary authorization is preferred over the primary (if provided).
closes https://github.com/elastic/elasticsearch/issues/53801
* fixing for backport
* [ML] add num_matches and preferred_to_categories to category defintion objects (#54214)
This adds two new fields to category definitions.
- `num_matches` indicating how many documents have been seen by this category
- `preferred_to_categories` indicating which other categories this particular category supersedes when messages are categorized.
These fields are only guaranteed to be up to date after a `_flush` or `_close`
native change: https://github.com/elastic/ml-cpp/pull/1062
* adjusting for backport
This commit corrects the description for the request URI index for the Multi Get (mget) API.
The index can only be a single index name (multiple or wildcard expressions not supported),
and acts as the index to use when "ids" are specified, or a document in the "docs" array does
not specify an index.
(cherry picked from commit aa4926ed7f91dfbf7973a01b1e4682e91dda11a9)
This commit adds a top-level link to the autoscaling API reference page
to the API docs. Additionally, we add a conditional guard on the API
pages to only include them in development builds of the docs.
EQL functions are an easy way for users to transform indexed data
at search time. However, using multiple functions can make
queries difficult to write and slows search speeds.
Users can circumvent this by indexing fields containing the transformed
data, but that usually slows index speeds.
This adds a related tip and example covering these tradeoffs.
This commit is the first in a series of commits that introduces
autoscaling policies, and APIs for working with them. For now, we
introduce the basic infrastructure, and a single API for putting an
autoscaling policy. We will follow in rapid succession with APIs for
getting, and deleting autoscaling policies.
This is a simple naming change PR, to fix the fact that "metadata" is a
single English word, and for too long we have not followed general
naming conventions for it. We are also not consistent about it, for
example, METADATA instead of META_DATA if we were trying to be
consistent with MetaData (although METADATA is correct when considered
in the context of "metadata"). This was a simple find and replace across
the code base, only taking a few minutes to fix this naming issue
forever.
The anchor ID for the snapshot repository plugins section in the docs
was recently changes from `_repository_plugins` to
`snapshots-repository-plugins`.
This adds a corresponding redirect so no links are broken.
Remove mention of the `yellow` and `red` starting
health status from the rolling upgrade docs.
Instead, we should emphasize that users wait
for the node to recover with a health status of
`green` rather than the starting status.
Co-authored-by: James Rodewig <james.rodewig@elastic.co>
Fixing the naming of the HLRC values to match the ToXContent field names (i.e. the field names returned from an API call).
Also fixes the names in the _cat API as well.
closes#53946
This setting is not documented and has dubious value since it means
there can be nodes in the cluster (non-data and non-master nodes) that
do not have persistent node IDs. This does not have any use cases so
this commit removes the setting.
The failing suggester documentation test was expecting specific scores in the
test response, which is fragile implementation details that e.g. can change with
different lucene versions and generally shouldn't be done in documentation test.
Instead we usually replace the float values in the output response by the ones
in the actual response.
Closes#54257
The remove keystore command can handle multiple settings. In a few
places, we were not consistent about mentioning this. This commit
addreses this, in the CLI help, and the docs.
This commit renames wait_for_completion to wait_for_completion_timeout in submit async search and get async search.
Also it renames clean_on_completion to keep_on_completion and turns around its behaviour.
Closes#54069
Today the keystore add-file command can only handle adding a single
setting/file pair in a single invocation. This incurs the startup costs
of the JVM many times, which in some environments can be expensive. This
commit teaches the add-file keystore command to accept adding multiple
settings in a single invocation.
The documentation was missing the long option for the force option, and
the short option for the stdin option. This commit addresses this by
adding these to the documentation.
Today the keystore add command can only handle adding a single
setting/value pair in a single invocation. This incurs the startup costs
of the JVM many times, which in some environments can be expensive. This
commit teaches the add keystore command to accept adding multiple
settings in a single invocation.
Adds documentation for the EQL `substring` function.
Supporting changes:
* Creates a new "EQL function reference" page
* Updates the title of the "EQL syntax reference" page for consistency
* Adds a brief "Functions" section to the EQL syntax docs
* Updates EQL limitations docs to state that only array functions are
unsupported
Makes the following changes to the `keyword_marker` token filter docs:
* Rewrites description and adds Lucene link
* Adds detailed analyze example
* Rewrites parameter definitions
* Adds custom analyzer and filter example
Documents missing data types for several response parameters returned
by the node stats API.
Also adds several missing human-readable parameters returned by the API.
Currently the remote info api has added a number of possible fields
(proxy, num_socket_connections, etc) that are available in proxy mode.
These fields are not aligned with what the settings are named. This
commit modifies this API to align with the settings.
Submit async search forces pre_filter_shard_size for the underlying search that it creates.
With this commit we also prevent users from overriding such default as part of request validation.
It is possible for ML jobs to open lazily if the "allow_lazy_open"
option in the job config is set to true. Such jobs wait in the
"opening" state until a node has sufficient capacity to run them.
This commit fixes the bug that prevented datafeeds for jobs lazily
waiting assignment from being started. The state of such datafeeds
is "starting", and they can be stopped by the stop datafeed API
while in this state with or without force.
Backport of #53918
add 2 additional stats: processing time and processing total which capture the
time spent for processing results and how often it ran. The 2 new stats
correspond to the existing indexing and search stats. Together with indexing
and search this now allows the user to see the full picture, all 3 stages.
This is the first in a series of commits that will introduce the
autoscaling deciders framework. This commit introduces the basic
framework for representing autoscaling decisions.
This commit changes the pre_filter_shard_size default from 128 to unspecified.
This allows to apply heuristics based on the request and the target indices when deciding
whether the can match phase should run or not. When unspecified, this pr runs the can match phase
automatically if one of these conditions is met:
* The request targets more than 128 shards.
* The request contains read-only indices.
* The primary sort of the query targets an indexed field.
Users can opt-out from this behavior by setting the `pre_filter_shard_size` to a static value.
Closes#39835
It seemed confusing for users that our top-level mapping page still had a
prominent section named 'Mapping Type'. This PR reworks the docs to remove this
reference and adds a note about types removal (similar to the note we added to
other APIs like put mapping).
* Get Async Search: omit _clusters section when empty (#53907)
The _clusters section is omitted by the search API whenever no remote clusters are searched. Async search should do the same, but Get Async Search returns a deserialized response, hence a weird `_clusters` section with all values set to `0` gets returned instead. In fact the recreated Clusters object is not the same object as the EMPTY constant, yet it has the same content.
This commit addresses this by changing the comparison in the `toXContent` method to not print out the section if the number of total clusters is `0`.
* Async search: remove version from response (#53960)
The goal of the version field was to quickly show when you can expect to find something new in the search response, compared to when nothing has changed. This can also be done by looking at the `_shards` section and `num_reduce_phases` returned with the search response. In fact when there has been one or more additional reduction of the results, you can expect new results in the search response. Otherwise, the `_shards` section could notify of additional failures of shards that have completed the query, but that is not a guarantee that their results will be exposed (only when the following partial reduction is performed their results will be available).
That said this commit clarifies this in the docs and removes the version field from the async search response
* Async Search: replicas to auto expand from 0 to 1 (#53964)
This way single node clusters that are green don't go yellow once async search is used, while
all the others still have one replica.
* [DOCS] address timing issue in async search docs tests (#53910)
The docs snippets for submit async search have proven difficult to test as it is not possible to guarantee that you get a response that is not final, even when providing `wait_for_completion=0`. In the docs we want to show though a proper long-running query, and its first response should be partial rather than final.
With this commit we adapt the docs snippets to show a partial response, and replace under the hood all that's needed to make the snippets tests succeed when we get a final response. Also, increased the timeout so we always get a final response.
Closes#53887Closes#53891
The joda to java.time migration requires users to upgrade their mappings. We allow them to still use 6.x created indices with joda patterns in 7 but ask them to upgrade their patterns in 7.x.
This migration guide is to help them understand how they could be affected and what needs to be changed in their mappings.
closes#51614closes#51236
The terms-lookup section of our terms query docs currently state that the
index, id and path fields are optional. They should be marked instead
as required.
Backport to 7x
Enable geo_shape query to work on geo_point fields for shapes: circle, polygon, multipolygon, rectangle see: #48928
Co-Authored-By: @iverase
Adds conceptual docs for token graphs.
These docs cover:
* How a token graph is constructed from a token stream
* How synonyms and multi-position tokens impact token graphs
* How token graphs are used during search
* Why some token filters produce invalid token graphs
Also makes the following supporting changes:
* Adds anchors to the 'Anatomy of an Analyzer' docs for cross-linking
* Adds several SVGs for token graph diagrams
Removes the `flat_settings` and `timeout` query parameters from the JSON
spec and asciidoc docs for the put index template API.
These parameters are not supported by the API.
It is useful to be able to delay state recovery until enough data nodes have
joined the cluster, since this gives the shard allocator a decent opportunity
to re-use as much existing data as possible. However we also have the option to
delay state recovery until a certain number of master-eligible nodes have
joined, and this is unnecessary: we require a majority of master-eligible nodes
for state recovery, and there is no advantage in waiting for more.
This commit deprecates the unnecessary settings in preparation for their
removal.
Relates #51806
This commit adjusts a `deprecation[...]` message in the docs since such
messages must be on a single line. It also moves this message to the start of
the description of the deprecated setting as is the case with other such
messages.
* Submit async search to work only with POST (#53368)
Currently the submit async search API can be called using both GET and POST at REST, but given that it submits a call and creates internal state, POST should be the only allowed method.
* Refine SearchProgressListener internal API (#53373)
The following cumulative improvements have been made:
- rename `onReduce` and `notifyReduce` to `onFinalReduce` and `notifyFinalReduce`
- add unit test for `SearchShard`
- on* methods in `SearchProgressListener` shouldn't need to be public as they should never be called directly, they only need to be overridden hence they can be made protected. They are actually called directly from a test which required some adapting, like making `AsyncSearchTask.Listener` class package private instead of private
- Instead of overriding `getProgressListener` in `AsyncSearchTask`, as it feels weird to override a getter method, added a specific method that allows to retrieve the Listener directly without needing to cast it. Made the getter and setter for the listener final in the base class.
- rename `SearchProgressListener#searchShards` methods to `buildSearchShards` and make it static given that it accesses no instance members
- make `SearchShard` and `SearchShardTask` classes final
* Move async search yaml tests to x-pack yaml test folder (#53537)
The yaml tests for async search currently sit in its qa folder. There is no reason though for them to live in a separate folder as they don't require particular setup. This commit moves them to the main folder together with the other x-pack yaml tests so that they will be run by the client test runners too.
* [DOCS] Add temporary redirect for async-search (#53454)
The following API spec files contain a link to a not-yet-created
async search docs page:
* [async_search.delete.json][0]
* [async_search.get.json][1]
* [async_search.submit.json][2]
The Elaticsearch-js client uses these spec files to create their docs.
This created a broken link in the Elaticsearch-js docs, which has broken
the docs build.
This PR adds a temporary redirect for the docs page. This redirect
should be removed when the actual API docs are added.
[0]: https://github.com/elastic/elasticsearch/blob/master/x-pack/plugin/src/test/resources/rest-api-spec/api/async_search.delete.json
[1]: https://github.com/elastic/elasticsearch/blob/master/x-pack/plugin/src/test/resources/rest-api-spec/api/async_search.get.json
[2]: https://github.com/elastic/elasticsearch/blob/master/x-pack/plugin/src/test/resources/rest-api-spec/api/async_search.submit.json
Co-authored-by: James Rodewig <james.rodewig@elastic.co>
* Removes experimental.
* Replaces `"v"` (for value) with `"m"` (for metric).
* Move the note about tiebreaking into the list of limitations of the
sort.
* Explain how you ask for `metrics`.
* Clean up some wording.
* Link to the docs from `top_metrics`.
Closes#51813
Makes the following changes to the `remove_duplicates` token filter
docs:
* Rewrites description and adds Lucene link
* Adds detailed analyze example
* Adds custom analyzer example
* New wildcard field optimised for wildcard queries (#49993)
Indexes values using size 3 ngrams and also stores the full original as a binary doc value.
Wildcard queries operate by using a cheap approximation query on the ngram field followed up by a more expensive verification query using an automaton on the binary doc values. Also supports aggregations and sorting.
Keyword field values with length more than ignore_above are not
indexed. But highlighters still were retrieving these values
from _source and were trying to highlight them. This sometimes lead to
errors if a field length exceeded max_analyzed_offset. But also this
is an overall wrong behaviour to attempt to highlight something that was
ignored during indexing.
This PR checks if a keyword value was ignored because of its length,
and if yes, skips highlighting it.
Backport: #53408Closes#43800
Adds a new parameter for classification that enables choosing whether to assign labels to
maximise accuracy or to maximise the minimum class recall.
Fixes#52427.
This changes the `top_metrics` aggregation to return metrics in their
original type. Since it only supports numerics, that means that dates,
longs, and doubles will come back as stored, with their appropriate
formatter applied.
This change removes the Lucene's experimental flag from the documentations of the following
tokenizer/filters:
* Simple Pattern Split Tokenizer
* Simple Pattern tokenizer
* Flatten Graph Token Filter
* Word Delimiter Graph Token Filter
The flag is still present in Lucene codebase but we're fully supporting these tokenizers/filters
in ES for a long time now so the docs flag is misleading.
Co-authored-by: James Rodewig <james.rodewig@elastic.co>
Restructures the 'Update an enrich policy' section to:
* Migrate the content to the section. It was previously stored in the
Put Enrich Policy API docs.
* Remove the warning tag admonition from the section content.
* Replace a reused section earlier in the "Set up an enrich processor"
page with a link.
No substantive changes were made to the content.
Adds a new `default_field_map` field to trained model config objects.
This allows the model creator to supply field map if it knows that there should be some map for inference to work directly against the training data.
The use case internally is having analytics jobs supply a field mapping for multi-field fields. This allows us to use the model "out of the box" on data where we trained on `foo.keyword` but the `_source` only references `foo`.
Makes the following changes to the `word_delimiter` token filter docs:
* Adds a warning admonition recommending the `word_delimiter_graph`
filter instead. This warning includes a link to the deprecated Lucene
`WordDelimiterFilter`.
* Updates the description
* Adds detailed analyze snippet
* Adds custom analyzer and custom filter snippets
* Reorganizes and updates parameter documentation
In a tip admonition, we recommend using the `keyword` tokenizer with the
`word_delimiter_graph` token filter. However, we only use the
`whitespace` tokenizer in the example snippets. This updates those
snippets to use the `keyword` tokenizer instead.
Also corrects several spacing issues for arrays in these docs.
Updates the SVG for a token graph to make the layout consistent with
other graphs. This means moving the text directly above the edge lines.
Previously, the text was above the edge line.
Adds a tip admonition to the basic example in the EQL search docs.
This tip lets users know they can set up a Beat to automatically
index data in ES, rather than manually indexing using the bulk or index
APIs.
Documents the `nodes` response parameters returned by the
`_cluster/stats` API.
Also adds collapsible attributes for the `indices` and `nodes`
sections.
Makes the following changes to the `word_delimiter_graph` token filter
docs:
* Updates the Lucene experimental admonition.
* Updates description
* Adds analyze snippet
* Adds custom analyzer and custom filter snippets
* Reorganizes and updates parameter list
* Expands and updates section re: differences between `word_delimiter`
and `word_delimiter_graph`
This commit introduces hidden aliases. These are similar to hidden
indices, in that they are not visible by default, unless explicitly
specified by name or by indicating that hidden indices/aliases are
desired.
The new alias property, `is_hidden` is implemented similarly to
`is_write_index`, except that it must be consistent across all indices
with a given alias - that is, all indices with a given alias must
specify the alias as either hidden, or all specify it as non-hidden,
either explicitly or by omitting the `is_hidden` property.