Currently, there are some useless includes in the codebase. We can use a tool named include-what-you-use to optimize these includes. By using a strict include-what-you-use policy, we can get lots of benefits from it.
doris on es8 can not work, because type change. The use of type is no longer recommended in es7,
and support for type has been removed from es8.
1. /_mapping not support include_type_name
2. /_search not support use type
At present, the application of vlog in the code is quite confusing.
It is inherited from impala VLOG_XX format, and there is also VLOG(number) format.
VLOG(number) format does not have a unified specification, so this pr standardizes the use of VLOG
Prior to this PR, Doris On ES merged another PR https://github.com/apache/incubator-doris/pull/3513 which misusing the `total` node. After Doris On ES introduce `terminate_after` (https://github.com/apache/incubator-doris/issues/2576), the `total` documents would not be computed, rely on this `total` field would be dangerous， we just rely on the actual document count by counting the `inner hits` node which it means to be. So we just remove all total parsing and related logic from Doris On ES, this maybe improve performance slightly because of ignoring and skipping `total` json node.
The other PR : https://github.com/apache/incubator-doris/pull/3513 (https://github.com/apache/incubator-doris/issues/3479) try to resolved the `inner hits node is not an array` because when a query( batch-size) run against new segment without this field, as-well the filter_path just only take `hits.hits.fields` 、`hits.hits._source` into account, this would appear an null inner hits node:
```
{
"_scroll_id": "DXF1ZXJ5QW5kRmV0Y2gBAAAAAAAAHaUWY1ExUVd0ZWlRY2",
"hits": {
"total": 1
}
}
```
Unfortunately this PR introduce another serious inconsistent result with different batch_size because of misusing the `total`.
To avoid this two problem, we just add `hits.hits._score` to filter_path when `docvalue_mode` is true, `_score` would always `null` , and populate the inner hits node:
```
{
"_scroll_id": "DXF1ZXJ5QW5kRmV0Y2gBAAAAAAAAHaUWY1ExUVd0ZWlRY2",
"hits": {
"total": 1,
"hits": [
{
"_score": null
}
]
}
}
```
related issue: https://github.com/apache/incubator-doris/issues/3752
#3479
Here I try to explain the cause of the problem and how to fix it.
**The Cause of The problem**
Take the case in issue(#3479 ) as an example:
The general results are as follows:
```
GET table/_doc/_search
{"query":{"match_all":{}},"stored_fields":"_none_","docvalue_fields":["k1"],"sort":["_doc"],"size":100}
{
"took": 6,
"timed_out": false,
"_shards": {
……
},
"hits": {
"total": 3,
"max_score": null,
"hits": [
{
"_index": "table",
"_score": null,
"sort": [
0
]
},
{
"_index": "table",
"_score": null,
"fields": {
"k1": [
"kkk1"
]
},
"sort": [
0
]
},
{
"_index": "table",
"_score": null,
"sort": [
0
]
}
]
}
}
```
But in Doris on ES，Be fetched data parallelly on all shards, and use `filter_path` to reduce the network cost. The process will be as follows:
```
GET table/_doc/_search?preference=_shards:1&filter_path=_scroll_id,hits.hits._source,hits.total,_id,hits.hits._source.fields,hits.hits.fields
{"query":{"match_all":{}},"stored_fields":"_none_","docvalue_fields":["k1"],"sort":["_doc"],"size":100}
{
"hits": {
"total": 0
}
}
GET table/_doc/_search?preference=_shards:2&filter_path=_scroll_id,hits.hits._source,hits.total,_id,hits.hits._source.fields,hits.hits.fields
{"query":{"match_all":{}},"stored_fields":"_none_","docvalue_fields":["k1"],"sort":["_doc"],"size":100}
{
"hits": {
"total": 1
}
}
GET table/_doc/_search?preference=_shards:3&filter_path=_scroll_id,hits.hits._source,hits.total,_id,hits.hits._source.fields,hits.hits.fields
{"query":{"match_all":{}},"stored_fields":"_none_","docvalue_fields":["k1"],"sort":["_doc"],"size":100}
{
"hits": {
"total": 1,
"hits": [
{
"fields": {
"k1": [
"kkk1"
]
}
}
]
}
}
```
*Scan-Worker On BE which processed result of shard2 will failed.*
**The reasons are as follows:**
1. "filter_path" causes the hits.hits object not exist.
2. In the current implementation, if there are some data rows（total > 0）, the hits.hits. object must be an array
**How To Fix it**
Two Method:
1. modify "filter_path" to contain the hits.
Pros: Fixed Code is very simple
Cons: More network cost
2. Deal with the case where fields are missing in a batch.
Pros: No loss of performance
Cons: Code is more complex
Performance first, I use Method2.
**Design**
1. Add a variable "_doc_value_mode" into Class "EsScrollParser" to =indicate whether the data processed by this parser is doc_value_mode or not.
2. "_doc_value_mode" is passed from ESScollReader <- ESScanner <- ScrollQueryBuilder::build() that determines whether DSL is enable doc_value_mode
3. When hits.hits of response from ES is empty and total > 0. We know there are data lines, but the corresponding fields do not exist. EsScrollParser will use "_doc_value_mode" and _total to construct _total lines which fields are assigned with 'NULL'
Pure DocValue optimization for doris-on-es
Future todo:
Today, for every tuple scan we check if pure_docvalue is enabled, this is not reasonable, should check pure_docvalue enabled for one whole scan outside, I will add this todo in future
Enhance doris on es error message and modify some field data transform error.
For varchar/char type, sometimes elasticsearch user post some not-string value to Elasticsearch Index. because of reading value from _source, we can not process all json type and then just transfer the value to original string representation this may be a tricky, but we can workaround this issue
