feat(doris-best-practices): add tablet count vs metadata & write-throughput limits rule

README.md

@@ -25,7 +25,7 @@ skill from its `description`, so in practice you describe the problem and the ri
 
 | Skill | What it does | Use it when |
 |---|---|---|
-| [`doris-best-practices`](skills/doris-best-practices/) | Table design, sizing, and runtime query investigation (37 rules, 7 use-case templates, 4 sizing guides) | Writing or reviewing `CREATE TABLE`, choosing a data model, partition/bucket strategy, or cluster configuration |
+| [`doris-best-practices`](skills/doris-best-practices/) | Table design, sizing, and runtime query investigation (38 rules, 7 use-case templates, 4 sizing guides) | Writing or reviewing `CREATE TABLE`, choosing a data model, partition/bucket strategy, or cluster configuration |
 | [`doris-architecture-advisor`](skills/doris-architecture-advisor/) | Workload-aware architecture design (8 decision rules, 10 worked industry examples) | Turning a business workload into a Doris design — model choice, ingestion strategy, sizing-first planning |
 | [`doris-debug`](skills/doris-debug/) | Production diagnostic suite: symptom router + 10 domain skills (query, import, compaction, node, MV, tablet, deployment, data-lake, resource-isolation, cloud), 16 case files, 45 case patterns | Something is broken — slow queries, failing imports, `-235` compaction errors, OOM or crashing nodes, an MV that will not rewrite, degraded tablets |
 | [`doris-profile-reader`](skills/doris-profile-reader/) | Query runtime profile interpretation and bottleneck triage (counter semantics, join-order / runtime-filter diagnosis, 9 reference guides) | You have a profile, query id, or profile URL and need to know what actually made the query slow |

skills/doris-best-practices/SKILL.md

@@ -28,7 +28,7 @@ metadata:
 # Apache Doris Best Practices
 
 > Problem-first table design intelligence for Apache Doris.
-> 37 rules, 7 use case templates, 4 sizing guides.
+> 38 rules, 7 use case templates, 4 sizing guides.
 > All details in `references/` directory.
 
 ---
@@ -276,12 +276,13 @@ Sizing guides are in:
 - `schema-partition-auto-on-demand` — AUTO for sporadic data
 - `schema-partition-skip-for-small` — Skip partitioning under 1 GB
 
-### Bucket Strategy — CRITICAL (5 rules)
+### Bucket Strategy — CRITICAL (6 rules)
 - `schema-bucket-hash-vs-random` — HASH for pruning, RANDOM for DUP only
 - `schema-bucket-high-cardinality-key` — Choose high-cardinality column
 - `schema-bucket-composite-for-skew` — Composite key to fix data skew
 - `schema-bucket-target-size` — Target 1-10 GB per tablet
 - `schema-bucket-cloud-mandatory-hash` — Cloud MoW requires HASH
+- `schema-bucket-tablet-count-limits` — Tablet count vs FE memory (10M ≈ 100 GB) and BE (<20k); <128 buckets/partition
 
 ### Sort Key — CRITICAL (5 rules)
 - `schema-keys-selectivity-first` — High selectivity first

skills/doris-best-practices/references/schema-bucket-tablet-count-limits.md

@@ -0,0 +1,28 @@
+---
+title: Control Tablet Count — Metadata Scale and Write-Throughput Limits
+impact: HIGH
+impactDescription: "Excess tablets exhaust FE metadata memory and fragment writes into many small files"
+tags: [schema, bucket, tablet, metadata, limits, write-throughput]
+---
+
+## Control Tablet Count — Metadata Scale and Write-Throughput Limits
+
+**Impact: HIGH — Too many tablets both exhaust FE metadata memory and fragment writes into many small files.**
+
+### Metadata scale (FE / BE)
+
+- **FE:** every 10 million tablets require roughly 100 GB of FE memory.
+- **BE:** a single BE should hold fewer than 20,000 tablets.
+
+### Write throughput
+
+- **Buckets per partition:** keep below 128 — more buckets significantly degrade write performance.
+- **Concentrate each write** on a small number of partitions to avoid scattered writes producing many small files.
+
+### Related rules
+
+- Partition column → time or low-cardinality enum: `schema-partition-*`
+- Bucket column → high cardinality (e.g. `user_id`): `schema-bucket-high-cardinality-key`
+- Single tablet size → 1–10 GB: `schema-bucket-target-size`
+
+Reference: [Basic Concepts](https://doris.apache.org/docs/table-design/data-partitioning/basic-concepts)