elasticsearch exceeds memory after few hours - elasticsearch

Question

In our system, 5000-15000 records written to elasticsearch(1.7.3) per minute, for first 4-5 hours its fine but after then it starts slowing down and almost no response any read or write request. After we restart elastic service its works fine for 4-5 hours again..
When elasticsearch starts slowing I checked the memory its about %95 so I think this is the reason why its broken but I dont understand why its loading RAM and never flush it.. No point of increasing ram, We have 8 GB RAM and elastic reached %95 of it in 5 hours..
Is there anything handle this? flush memory or auto restart elastic etc. ?
EDITED
Here is sample document in index:
"hits": {
"total": 18083446,
"max_score": 1,
"hits": [
{
"_index": "userlogs",
"_type": "userlogstype",
"_id": "AVMZEEYwW1W7iq27fTcE",
"_score": 1,
"_source": {
"domain": "http://gatr.hit.gemius.pl/",
"url": "http://gatr.hit.gemius.pl/_1456414408406/rexdot.js?",
"filetype": "-",
"clientname": "NOTINDOMAIN",
"clientmac": "00:0c:29:8f:c4:4f",
"hierarchycode": "HIER_DIRECT/188.165.145.88",
"user": "-",
"duration": "168",
"respsize": "1059",
"clientip": "10.6.1.130",
"loggingdate": "25/02/2016 17:33:28",
"resultcode": "TCP_MISS/301",
"reqmethod": "GET"
}
},
{
"_index": "userlogs",
"_type": "userlogstype",
"_id": "AVMZEEYwW1W7iq27fTcI",
"_score": 1,
"_source": {
"domain": "http://10.6.2.212/",
and here is mapping of index:
{
"webproxylog": {
"mappings": {
"update_by_query": {
"properties": {
"query": {
"properties": {
"filtered": {
"properties": {
"filter": {
"properties": {
"term": {
"properties": {
"url": {
"type": "string"
}
}
}
}
}
}
}
}
},
"script": {
"type": "string"
}
}
},
"accesslog": {
"properties": {
"action": {
"type": "string",
"index": "not_analyzed"
},
"action4cat": {
"type": "string",
"index": "not_analyzed"
},
"category": {
"type": "string"
},
"clientip": {
"type": "string",
"index": "not_analyzed"
},
"clientmac": {
"type": "string",
"index": "not_analyzed"
},
"clientname": {
"type": "string",
"index": "not_analyzed"
},
"domain": {
"type": "string",
"index": "not_analyzed"
},
"duration": {
"type": "long"
},
"filetype": {
"type": "string",
"index": "not_analyzed"
},
"hierarchycode": {
"type": "string",
"index": "not_analyzed"
},
"index": {
"properties": {
"_index": {
"type": "string"
},
"_type": {
"type": "string"
}
}
},
"loggingdate": {
"type": "date",
"format": "dd/MM/yyyy HH:mm:ss"
},
"reqmethod": {
"type": "string",
"index": "not_analyzed"
},
"respsize": {
"type": "long"
},
"resultcode": {
"type": "string",
"index": "not_analyzed"
},
"url": {
"type": "string",
"index": "not_analyzed"
},
"user": {
"type": "string",
"index": "not_analyzed"
}
}
}
}
}
}
query sample :
{
"size": 0,
"query": {
"filtered": {
"filter": {
"bool": {
"must": [
{
"exists": {
"field": "instock"
}
},
{}
]
}
}
}
},
"aggs": {
"aggs1": {
"terms": {
"field": "clientname",
"size": 5,
"order": {
"aggs2": "desc"
}
},
"aggs": {
"aggs2": {
"sum": {
"field": "respsize"
}
}
}
}
}
}