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Why would a ~3GB database consume 10+GB of server RAM?

abed_halawi
Node Link

This is a causal cluster of 3 instances (1 leader, 2 followers).

 

Below are the :sysinfo data:

 

Store Sizes
Count Store 35.00 KiB
Label Store 279.29 KiB
Index Store 733.22 MiB
Schema Store 200.01 KiB
Array Store 595.73 MiB
Logical Log 38.95 MiB
Node Store 54.09 MiB
Property Store 643.38 MiB
Relationship Store 74.56 MiB
String Store 504.52 MiB
Total Store Size 2.93 GiB
ID Allocation
Node ID 3780265
Property ID 16441803
Relationship ID 2267527
Relationship Type ID 321
Page Cache
Faults 331005
Evictions 0
File Mappings 169
Bytes Read 2652192417
Flushes 14565
Eviction Exceptions 0
File Unmappings 120
Bytes Written 596435804
Hit Ratio 99.99%
Usage Ratio 84.51%
Transactions
Last Tx Id 61236362
Current 1
Peak 2
Opened 23740
Committed 23703

 

Pagecache and heap size config:

 

  • dbms.memory.heap.initial_size: 5G
  • dbms.memory.heap.max_size: 5G
  • dbms.memory.pagecache.size: 3G
3 REPLIES 3

Hi Abed, long time no see 🙂

Because that's your configuration:

5G heap + 3G pagecache = 8G

Depending on your operations that's what you need. the 3G pagecache maps the files from disk to memory.

And the heap is for ongoing operations and processing of your queries, you might be able to reduce the heap.

And because you have such a large string store which you hopefully don't access that often you could also get your pagecache down to 1G or so.

Michael my friend! Long time indeed 🙂 I hope you've been doing well.

I was under the impression that pagecache should be similar or greater than DB size for some reason to keep performance well. As for decreasing heap size, would that have any impact on performance too?

 

Yes smaller heap and PC might have performance impacts, for the PC it depends which part of the graph is frequently accessed.

For heap it depends on the number of concurrent operations and how much each of those needs for computation.

Best to test it on your staging environment with realistic load testing if reduced numbers have much impact.

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