docs: Add log store documentation

Author: fordN

README.md

@@ -115,6 +115,44 @@ Very large `graph-node` instances can also be configured using a
 the `graph-node` needs to connect to multiple chains or if the work of
 indexing and querying needs to be split across [multiple databases](./docs/config.md).
 
+#### Log Storage
+
+`graph-node` supports storing and querying subgraph logs through multiple backends:
+
+- **File**: Local JSON Lines files (recommended for local development)
+- **Elasticsearch**: Enterprise-grade search and analytics (for production)
+- **Loki**: Grafana's log aggregation system (for production)
+- **Disabled**: No log storage (default)
+
+**Quick example (file-based logs for local development):**
+```bash
+mkdir -p ./graph-logs
+
+cargo run -p graph-node --release -- \
+  --postgres-url $POSTGRES_URL \
+  --ethereum-rpc mainnet:archive:https://... \
+  --ipfs 127.0.0.1:5001 \
+  --log-store-backend file \
+  --log-store-file-dir ./graph-logs
+```
+
+Logs are queried via GraphQL at `http://localhost:8000/graphql`:
+```graphql
+query {
+  _logs(subgraphId: "QmYourSubgraphHash", level: ERROR, first: 10) {
+    timestamp
+    level
+    text
+  }
+}
+```
+
+**For complete documentation**, see the **[Log Store Guide](./docs/log-store.md)**, which covers:
+- How to configure each backend (Elasticsearch, Loki, File)
+- Complete GraphQL query examples
+- Choosing the right backend for your use case
+- Performance considerations and best practices
+
 ## Contributing
 
 Please check [CONTRIBUTING.md](CONTRIBUTING.md) for development flow and conventions we use.

docs/environment-variables.md

@@ -315,3 +315,55 @@ those.
   Disabling the store call cache may significantly impact performance; the actual impact depends on
   the average execution time of an `eth_call` compared to the cost of a database lookup for a cached result.
   (default: false)
+
+## Log Store Configuration
+
+`graph-node` supports storing and querying subgraph logs through multiple backends: Elasticsearch, Loki, local files, or disabled.
+
+**For complete log store documentation**, including detailed configuration, querying examples, and choosing the right backend, see the **[Log Store Guide](log-store.md)**.
+
+### Quick Reference
+
+**Backend selection:**
+- `GRAPH_LOG_STORE_BACKEND`: `disabled` (default), `elasticsearch`, `loki`, or `file`
+
+**Elasticsearch:**
+- `GRAPH_LOG_STORE_ELASTICSEARCH_URL`: Elasticsearch endpoint URL (required)
+- `GRAPH_LOG_STORE_ELASTICSEARCH_USER`: Username (optional)
+- `GRAPH_LOG_STORE_ELASTICSEARCH_PASSWORD`: Password (optional)
+- `GRAPH_LOG_STORE_ELASTICSEARCH_INDEX`: Index name (default: `subgraph`)
+
+**Loki:**
+- `GRAPH_LOG_STORE_LOKI_URL`: Loki endpoint URL (required)
+- `GRAPH_LOG_STORE_LOKI_TENANT_ID`: Tenant ID (optional)
+
+**File-based:**
+- `GRAPH_LOG_STORE_FILE_DIR`: Log directory (required)
+- `GRAPH_LOG_STORE_FILE_MAX_SIZE`: Max file size in bytes (default: 104857600 = 100MB)
+- `GRAPH_LOG_STORE_FILE_RETENTION_DAYS`: Retention period (default: 30)
+
+**Deprecated variables** (will be removed in future versions):
+- `GRAPH_ELASTICSEARCH_URL` → use `GRAPH_LOG_STORE_ELASTICSEARCH_URL`
+- `GRAPH_ELASTICSEARCH_USER` → use `GRAPH_LOG_STORE_ELASTICSEARCH_USER`
+- `GRAPH_ELASTICSEARCH_PASSWORD` → use `GRAPH_LOG_STORE_ELASTICSEARCH_PASSWORD`
+- `GRAPH_ELASTIC_SEARCH_INDEX` → use `GRAPH_LOG_STORE_ELASTICSEARCH_INDEX`
+
+### Example: File-based Logs for Local Development
+
+```bash
+mkdir -p ./graph-logs
+export GRAPH_LOG_STORE_BACKEND=file
+export GRAPH_LOG_STORE_FILE_DIR=./graph-logs
+
+graph-node \
+  --postgres-url postgresql://graph:pass@localhost/graph-node \
+  --ethereum-rpc mainnet:https://... \
+  --ipfs 127.0.0.1:5001
+```
+
+See the **[Log Store Guide](log-store.md)** for:
+- Detailed configuration for all backends
+- How log stores work internally
+- GraphQL query examples
+- Choosing the right backend for your use case
+- Best practices and troubleshooting