elasticsearch ngram and postgresql trigram search results are not match - postgresql

Question

I've crereated an index on elasticsearch same as bellow:
"settings" : {
"number_of_shards": 1,
"number_of_replicas": 0,
"analysis": {
"filter": {
"trigrams_filter": {
"type": "ngram",
"min_gram": 3,
"max_gram": 3
}
},
"analyzer": {
"trigrams": {
"type": "custom",
"tokenizer": "standard",
"filter": [
"lowercase",
"trigrams_filter"
]
}
}
}
},
"mappings": {
"issue": {
"properties": {
"description": {
"type": "string",
"analyzer": "trigrams"
}
}
}
}
My test items are bellow:
"alici onay verdi basarili satisiniz gerceklesti diyor ama hesabima para transferi gerceklesmemis"
"otomatik onay işlemi gecikmiş"
"************* nolu iade islemi urun kargoya verilmedi zamaninda iade islemlerinde urun erorr hata veriyor"
I've test this index with bellow query:
GET issue/_search
{
"query": {
"match": {
"description":{
"query": "otomatik onay istemi zamaninda gerceklesmemis"
}
}
}
}
And result:
{
....
"hits": {
....
"max_score": 2.3507352,
"hits": [
{
....
"_score": 2.3507352,
"_source": {
"issue_id": "*******",
"description": "alici onay verdi basarili satisiniz gerceklesti diyor ama hesabima para transferi gerceklesmemis"
}
}
]
}
}
But same data on postgresql with bellow SQL response another result:
SELECT
public.tbl_issue_descriptions_big.description,
similarity(description, 'otomatik onay islemi zamaninda gerceklesmemis') AS sml
FROM
public.tbl_issue_descriptions_big
WHERE
description %'otomatik onay islemi zamaninda gerceklesmemis'
ORDER BY
sml DESC
LIMIT 10
Result is:
description | sml
======================================================|======
otomatik onay islemi gecikmis |0,351852
Why is this difference caused?

Answer 1

I dont know enough about postgres to give a qualified answer there (as this also depends on the documents that are indexed and if they scoring formulas are exactly the same, which I doubt), but Elasticsearch has an explain API and an explain parameter in the search, that help you to find out why a certain document was scored this way.