Elasticsearch pagination does not work on 2.3.3

[piorus]

Preconditions (*)

Magento version 2.3.3
Elasticsearch 6.0
Stores->Configuration->Catalog->Catalog->Catalog Search->Search Engine = Elasticsearch 6.0+

Steps to reproduce (*)

NEW steps used for REOPEN on 2.4-develop -> #25038 (comment)

1. Set Elasticsearch 6.0 as search engine
2. bin/magento indexer:reindex
3. Go to category page that have more than one page
4. Navigate to second page

Expected result (*)

Products from the second page are displayed.

Actual result (*)

No products found.

More details

I've digged up in Magento's ES implementation and found really strange thing. Magento is requesting elasticsearch with from and size parameters that limits search results but additionally there is another limit in \Magento\Eav\Model\Entity\Collection\AbstractCollection::_loadEntities
$this->getSelect()->limitPage($this->getCurPage(), $this->_pageSize);

Result is as follow for second page of category listing:

1. Elasticsearch returns second page of products limited by from and size and magento is adding product IDs to the collection.
   Example ElasticSearch request:

POST /magento2_product_1/document/_search
{ 
   "from":9,
   "size":9,
   "stored_fields":[ 
      "_id",
      "_score"
   ],
   "sort":[ 
      { 
         "position_category_5":{ 
            "order":"asc"
         }
      }
   ],
   "query":{ 
      "bool":{ 
         "must":[ 
            { 
               "term":{ 
                  "category_ids":"5"
               }
            },
            { 
               "terms":{ 
                  "visibility":[ 
                     "2",
                     "4"
                  ]
               }
            }
         ]
      }
   },
   "aggregations":{ 
      "price_bucket":{ 
         "extended_stats":{ 
            "field":"price_0_1"
         }
      },
      "category_bucket":{ 
         "terms":{ 
            "field":"category_ids",
            "size":500
         }
      },
      "manufacturer_bucket":{ 
         "terms":{ 
            "field":"manufacturer",
            "size":500
         }
      },
      "color_bucket":{ 
         "terms":{ 
            "field":"color",
            "size":500
         }
      }
   }
}

2. Collection executes _loadEntities and add yet another limit which goes way out of collection
   s range and this leads to 0 results found.

[m2-assistant]

Hi @piotrusin. Thank you for your report.
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• yes
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[m2-assistant]

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[krishprakash]

Hi @piotrusin. Thank you for your report.
Seems Issue is already reported please review at #24047

[piorus]

@krishprakash i don't get how those two are related besides that both issues are related to elasticsearch. in this case there is no exception thrown, just empty result set due to duplicated limit/offset

[domeglic]

There is a patch for this, but it will also cause the pager to stop showing: example Instead of "Items 1-9 of 13" just "13 Items"

[piorus]

I've handled it by myself by adding before/after _loadEntities plugin on Magento\Catalog\Model\ResourceModel\Product\Collection that sets pageSize to 0 and resets it back after querying if using elasticsearch. This does not break pager.

[simonmaass]

I have the same issue after upgrading to m2.3.3. - in all category pages or search results i am unable to click on the next page!

[simonmaass]

btw this is also with elasticsearch 5x... not just 6x like the patch suggests