More_like_this The size of the problem

[Zyuxing]

I tried to use more_like_thisAPI, and found that there was a big time gap between size=0 and size=10. There was 30 million data, using a mechanical hard disk. I wonder if the step was slow.
The matching fields are indexed using the "term_vector": "yes" stored token vector.
Here's the difference between size=0 and size=10：
GET pubmed2/_search?size=0
{
"_source": ["PMID","abstractText*"],
"query": {
"more_like_this": {
"fields": [
"abstractText"
],
"like": """Gammaglutamyl transpeptidase is an enzyme primarily located in the brush border of the proximal convoluted tubules of the kidney. Its unique localisation in the renal cells most easily damaged by ischaemia and its ease of assay provides the rationale for its use in the measurement of renal ischaemic injury. Using a standard experimental animal model, canine urinary gamma-GT activity was shown to be increased up to 70-fold following 90 min of unilateral renal ischaemia and was significantly raised following only 5 min ischaemia. The urinary gamma-GT was used as a measure of ischaemic injury associated with renal transplantation in man and 20 consecutive patients undergoing kidney transplant were studied by daily 24-hour urinary gamma-GT estimations and excellent correlation was obtained between raised enzyme activity and the clinical diagnosis of transplant rejection."""
}
}
}
The results of:
{
"took" : 10,
"timed_out" : false,
"_shards" : {
"total" : 1,
"successful" : 1,
"skipped" : 0,
"failed" : 0
},
"hits" : {
"total" : {
"value" : 10000,
"relation" : "gte"
},
"max_score" : null,
"hits" :
}
}
size=10:
GET pubmed2/_search?size=10
{
"_source": ["PMID","abstractText*"],
"query": {
"more_like_this": {
"fields": [
"abstractText"
],
"like": """Gammaglutamyl transpeptidase is an enzyme primarily located in the brush border of the proximal convoluted tubules of the kidney. Its unique localisation in the renal cells most easily damaged by ischaemia and its ease of assay provides the rationale for its use in the measurement of renal ischaemic injury. Using a standard experimental animal model, canine urinary gamma-GT activity was shown to be increased up to 70-fold following 90 min of unilateral renal ischaemia and was significantly raised following only 5 min ischaemia. The urinary gamma-GT was used as a measure of ischaemic injury associated with renal transplantation in man and 20 consecutive patients undergoing kidney transplant were studied by daily 24-hour urinary gamma-GT estimations and excellent correlation was obtained between raised enzyme activity and the clinical diagnosis of transplant rejection."""
}
}
}
The results of:
{
"took" : 4777,
"timed_out" : false,
"_shards" : {
"total" : 1,
"successful" : 1,
"skipped" : 0,
"failed" : 0
},
"hits" : {
"total" : {
"value" : 10000,
"relation" : "gte"
},
"max_score" : 17.0,
"hits" : [
{...}
},