7 min read
Stale Reads on Read Replicas: MySQL vs PostgreSQL
Both MySQL and PostgreSQL replicas serve stale data by default. What differs is the toolbox: GTID waits and group replication consistency levels versus LSN tokens and remote_apply.
Database Field Notes
Notes for the problems that show up after launch: bad plans, awkward migrations, index debt, vacuum pressure, replica lag, and the small decisions that keep PostgreSQL, MySQL, MariaDB, and SQL Server easier to operate.
Featured Guides
Slow query optimization
Find the queries dragging your Postgres down, read their plans, and fix them in order of impact.
Read the guide →Index optimization
Which indexes to add, which to drop, and how to spot redundant index debt before it costs you writes.
Read the guide →Vacuum guide
How autovacuum works, when it falls behind, and how to keep bloat from eating your storage and your buffer cache.
Read the guide →Connection pooling
Sizing pools, PgBouncer modes, and how to stop idle-in-transaction sessions from exhausting max_connections.
Read the guide →Replication monitoring
Track lag, WAL throughput, and replication slots before they turn into stale reads or a full disk.
Read the guide →Browse by Topic
Backups and Durability
9 articlesBackups, restores, PITR, archive gaps, and recovery drills for PostgreSQL.
Cloud Providers
5 articlesAWS RDS, Azure Database for PostgreSQL, Google Cloud SQL, AlloyDB, and managed PostgreSQL monitoring notes.
Connections and Pooling
10 articlesConnection storms, pool saturation, PgBouncer behavior, and max_connections pressure.
CPU, Memory, and I/O
17 articlesCPU, memory, disk, temp files, checkpoints, buffers, and workload pressure.
Indexes
37 articlesIndex design, index debt, reindexing, constraint indexes, and evidence-driven DDL.
Locks and Transactions
22 articlesLock waits, deadlocks, blocking chains, idle transactions, and transaction hygiene.
MariaDB
56 articlesGalera clustering, InnoDB and Aria internals, replication, optimizer behavior, and MariaDB operations notes.
MySQL
107 articlesInnoDB internals, replication, locking, query performance, and MySQL operations notes.
pgvector and RAG
15 articlesHNSW, IVFFlat, recall, embedding search, and production RAG performance notes.
Replication and WAL
28 articlesReplica lag, WAL growth, failover readiness, hot standby behavior, and replication slots.
Slow Queries
38 articlesQuery plans, EXPLAIN ANALYZE, planner regressions, pagination, joins, and statistics.
SQL Server
47 articlesWait statistics, tempdb, Query Store, Always On availability groups, and SQL Server operations notes.
Vacuum and Bloat
16 articlesAutovacuum, dead tuples, bloat, wraparound, MVCC, freeze age, and visibility.
Latest Field Notes
7 min read
SQL Server Transaction Log VLF Management for Fast Recovery
A failover that should have taken two minutes took forty-seven because the log had 30,000 virtual log files. How autogrowth wrote that layout, what log_reuse_wait_desc is telling you, and how to rebuild the layout exactly once.
7 min read
SQL Server Sliding Window Partitioning: Lifecycle, Not Speed
The nightly purge had been deleting for six hours and generating 400 GB of log when they called me; the sliding-window replacement runs in 200 milliseconds. Partition functions, aligned indexes, SWITCH mechanics, and when partitioning is the wrong tool.
9 min read
SQL Server Statistics: The Fuel the Cardinality Estimator Runs On
The index existed and the seek was in the plan, but the estimate said one row and the table said fourteen million. How auto-update thresholds, sampling, and the ascending-key trap produce bad estimates, and how to triage them with sys.dm_db_stats_properties.
6 min read
Ad-Hoc Plan Cache Pollution: Single-Use Plans Eating SQL Server Memory
The instance had 128 GB of memory and the buffer pool could not hold fifteen minutes of hot data, because 41 GB of the plan cache was plans executed exactly once. Measuring single-use bloat and the three levers that actually…
7 min read
RESOURCE_SEMAPHORE Waits: When SQL Server Queries Queue for Memory
Every weekday at 9:05 the order system's p99 went from forty milliseconds to eleven seconds, caused by one report holding a twelve-gigabyte memory grant. How grants are sized, how to read the queue in sys.dm_exec_query_memory_grants, and how to fence the…
7 min read
MAXDOP and Cost Threshold for Parallelism: Stop Setting by Folklore
Setting MAXDOP to 1 because of CXPACKET waits amputates a feature to treat a symptom. NUMA-aware MAXDOP guidance, why the default threshold of 5 is ancient history, and where each setting should actually live.
7 min read
Implicit Conversions: The Silent Index Killer in SQL Server Plans
The parameter was nvarchar, the column was varchar, and four million rows got converted one at a time. How CONVERT_IMPLICIT turns seeks into scans, why ORMs cause it so reliably, and where to fix it for good.
7 min read
Autogrowth Is Unplanned Downtime: File Sizing and Instant File Initialization
The order database froze writes for forty-one seconds at peak load because the data file grew by 32 GB and SQL Server zeroed every byte of it first. Percent-growth compounding, Instant File Initialization, and the pre-sizing discipline that makes growth…
6 min read
SQL Server Columnstore and Batch Mode: An Execution Model, Not Compression
Columnstore cut a report from four minutes to six seconds until trickle inserts rotted the rowgroups. Rowgroups, segment elimination, the deltastore lifecycle, batch mode on rowstore, and when a plain btree still wins.