System configuration

Enhancing Memgraph's performance can sometimes involve optimizing operating system-level configurations. These adjustments primarily relate to the settings governing resource allocation and process management.

Handle numerous open files simultaneously

The fs.file-max parameter in Linux sets the maximum number of file handles that the Linux kernel will allocate. This adjustment is important when the system needs to handle numerous open files simultaneously. To adjust this parameter, do the following:

Increasing memory map areas

If users are working on a larger scale, there is a possibility that a transaction is hanging because Memgraph tries to allocate memory and it couldn’t as it was out of virtual memory space. User can adjust the vm.max_map_count parameter to define the maximum number of memory map areas a process can have.

Recommended values for the vm.max_map_count parameter

For optimal system performance, the vm.max_map_count value should be chosen in accordance with your system's RAM, aiming for approximately one memory map area per 128 KB of system memory.

Immediate adjustment

For instance, if your recommended vm.max_map_count value is 262144, run sudo sysctl -w vm.max_map_count=262144 to immediately increase the memory map area limit to 262,144. This change takes effect right away but lasts only until the next reboot.

Persistent adjustment

To ensure that changes to vm.max_map_count persist after a reboot, follow these steps:

Addressing stack overflow issues

Stack overflow issues may occur due to a large query in Memgraph. To address these issues, there are two possible approaches:

1. Increase the stack size
2. Split the query into smaller chunks

Increase the stack size

With Docker

docker run --rm -it --name memgraph --ulimit stack=33554432:33554432 -p 7687:7687 -p 7444:7444 memgraph/memgraph

docker exec memgraph sh -c "ulimit -a | grep stack"

Without Docker

memgraph soft stack 32768
memgraph hard stack 32768

ulimit -s

Split the query into smaller chunks

To avoid stack overflow, divide your large query into smaller parts. This approach requires careful handling of variables and node references across queries. For creating edges between nodes created in separate queries, use the MATCH clause to reference nodes from previous queries:

// First Query
CREATE (a:Node {id: 1});
// Second Query
MATCH (a:Node {id: 1})
CREATE (b:Node {id: 2}), (a)-[:RELATES_TO]->(b);

This method reduces the stack size required for each query, potentially avoiding the stack overflow issue.