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

[abed_halawi]

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

[michael_hunger]

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.

[abed_halawi]

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?

[michael_hunger]

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.