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__**Re-Index ElasticSearch**__

REF: https://www.thirdrocktechkno.com/blog/6-steps-to-reindex-elasticsearch-data/

There are potentially several situations where you may need to recreate the current Elastic Search index.  This article is being written to handle one of the most common causes related to field data-type mapping.

In a traditional relational database, schema definitions can be altered at runtime using ALTER TABLE commands.  With ElasticSearch, things are different as there is no predefined schema.  ElasticSearch instead dynamically creates data-type mapping for the current index as data arrives and is persisted.  Typically, we use time-based indices, so every month, a new index is created.  In the case of the MDC, for example, December 2021 performance data would have an index titled 'rdf_performance_2021-12', and January 2022 would start on a new index titled 'rdf_performance_2022-01', etc...

If such an affecting data-type change is released after the first of the month, this can lead to errors in the MDC Tracker log file (~/logs/spring-boot/tracker.log) such as:

<WRAP center round box 90%>
**//org.elasticsearch.ElasticsearchStatusException: Elasticsearch exception [type=mapper_parsing_exception, reason=failed to parse field [parameters.winlink1000OduAirSesState.currentValue] of type [float] in document with id 'HCKGgn0BEcj44NiWqUh6'. Preview of field's value: 'scanning']//**
</WRAP>

This error implies that the existing data mapping for the current ElasticSearch index was expecting data of type 'float' for 'parameters.winlink1000OduAirSesState.currentValue', but instead received the String value 'scanning'.  

To resolve this situation, the basic process is to look up existing indices, create a new schema with some manually specified data-type mapping, copy the existing index data to the new index, and then delete the old index.  Commands to perform this can be executed in a terminal connected to the 'esk' server instance, or wherever elasticsearch is running for the affected environment.

**To begin, log into the server running elasticsearch via SSH in a termanal window (i.e. newtowerqaesk1.err or the like).  Then:
**
**1.  Retrieve existing indices:
**
**RUN:
**
<WRAP center round box 80%>
curl -X GET 'http://localhost:9200/_cat/indices/%2A?v=&s=index:desc'
</WRAP>


**GET:
**
<WRAP center round box 95%>
health status index                     uuid                   pri rep docs.count docs.deleted store.size pri.store.size

yellow open   rdf_performance_2021-12   FrgUteO8SwWYAjr_bBzeTA   1   1        638            0        1mb            1mb

yellow open   rdf_performance_2021-11   voMR0stFQtKPQjbHgANC1Q   1   1        264            0    422.2kb        422.2kb

yellow open   rdf_performance_2021-10   2-mHh39YQ5KcKProClWfew   1   1        368            0    296.8kb        296.8kb

yellow open   rdf_performance_2021-09   tzSCZQ4oT7i5QwTxlgrqGw   1   1        588            0      1.3mb          1.3mb

yellow open   rdf_performance_2021-08   REg32Gq7SgKTVb8yf1WIRQ   1   1       1206            0      1.1mb          1.1mb

yellow open   rdf_performance_2021-07   4woX_ouOQBiXDn9lTwlBwg   1   1       1427            0    869.1kb        869.1kb

yellow open   rdf_performance_2021-06   U_crwMvPQdWVOjDWkWSv9Q   1   1       1790            0      1.6mb          1.6mb

yellow open   rdf_performance_2021-05   z1-fgYvcRvmQy49CKE6dYQ   1   1       3450            0      9.1mb          9.1mb

yellow open   rdf_performance_2020-12   3RhZur4bSGStlHCaJ2dTRQ   1   1        141            0    585.8kb        585.8kb

yellow open   rdf_configuration_2021-12 uOZyT7emTiKf2b5mzi1A1A   1   1          9            8     64.7kb         64.7kb

yellow open   rdf_configuration_2021-09 XOkql2N3SZOGwwnxN7Meqw   1   1        164           36    389.9kb        389.9kb

yellow open   rdf_configuration_2021-08 O4QHGSQsSkOY_ZGjMUq3xw   1   1         28            5       82kb           82kb

yellow open   rdf_configuration_2021-05 Yi1SfMwvRAi_CvSvWfOWtA   1   1        842           69    553.4kb        553.4kb

yellow open   rdf_configuration_2020-12 AS5lie_AQimpwOdEvr53gA   1   1          8           60    129.5kb        129.5kb

green  open   .tasks                    p9CUjGXYTbuR7R_frdGniA   1   0          1            0      6.3kb          6.3kb

green  open   .kibana_2                 aU5XyQEdT52d-mIx1zUapA   1   0          3            0     60.8kb         60.8kb

green  open   .kibana_1                 4Y2825ANSFKddgNQeKsINg   1   0          1            0        4kb            4kb
</WRAP>



**2.  Create a new index for the data. In this example, we want to update mapping for:  **'parameters.winlink1000OduAirSesState.currentValue'** and **'parameters.winlink1000OduAirSesState.newValue'**.
**
**RUN: 
**
<WRAP center round box 90%>
curl -X PUT \http://localhost:9200/rdf_performance_2021-12_v2 \-H 'Content-Type: application/json' \-d '{
    "mappings": {
        "properties": {
               "parameters.winlink1000OduAirSesState.currentValue": {
                    "type": "text"
                },
                "parameters.winlink1000OduAirSesState.newValue": {
                	"type": "text"
                }
        }
    }
}'
</WRAP>


**GET:
**
<WRAP center round box 90%>
{"acknowledged":true,"shards_acknowledged":true,"index":"rdf_performance_2021-12_v3"}

</WRAP>


**3.  Transfer data into new index, very important.  Do not proceed if this step fails.  If it does for any reason, start over again with a new index name to transfer to.
**
**RUN (IF YOU CUT AND PASTE, REDUCE LINE SPACES, IMPORTANT):
**
<WRAP center round box 90%>
curl -X POST \
    http://localhost:9200/_reindex \
    -H 'Content-Type: application/json' \
    -d '{
    "source": {
        "index": "rdf_performance_2021-12"
    },
    "dest": {
        "index": "rdf_performance_2021-12_v2"
    }
}'
</WRAP>


**GET:
**
<WRAP center round box 90%>
{"took":927,"timed_out":false,"total":638,"updated":0,"created":638,"deleted":0,"batches":1,"version_conflicts":0,"noops":0,"retries":{"bulk":0,"search":0},"throttled_millis":0,"requests_per_second":-1.0,"throttled_until_millis":0,"failures":[]}
</WRAP>


**4.  Verify  (This step does not always work for some reason, though it is ok if it fails)
**
**RUN:
**
<WRAP center round box 90%>
curl -X GET \

'http://localhost:9200/rdf_performance_2021-12_v2/_search?scroll=10m&size=50' \
-H 'Content-Type: application/json' \
-d '{
    "query" : {
        "match_all" : {}
    }
}'
</WRAP>

**5.  Delete old index since the transfer in step 3 went well.  Again, if the transfer failed, do not proceed, start over.
**
**RUN:
**
<WRAP center round box 90%>
curl -X DELETE \
http://localhost:9200/rdf_performance_2021-12
</WRAP>

**GET:
**
<WRAP center round box 80%>
{"acknowledged":true}
</WRAP>

**6. Add new index finalized with an alias to the previous in case anything is specifically looking for the old key... which should not happen... but just to be safe.
**
**RUN:  
**
<WRAP center round box 90%>
curl -X POST \
http://localhost:9200/_aliases \
-H 'Content-Type: application/json' \
-d '{
    "actions": [
        {
            "add": {
                "index": "rdf_performance_2021-12_v2",
                "alias": "rdf_performance_2021-12"
            }
        }
    ]
}'
</WRAP>


**GET: 
**
<WRAP center round box 90%>
{"acknowledged":true}
</WRAP>


**7. ALL DONE!**
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