PostgreSQL 9.0 High Performance

Transcription

1 PostgreSQL 9.0 High Performance Accelerate your PostgreSQL system and avoid the common pitfalls that can slow it down Gregory Smith FPftf ITfl open source l a a 4%3 a l ^ o I community experience distilled PUBLISHING BIRMINGHAM - MUMBAI ULB Darmstadt

2 Preface 1 Chapter 1: PostgreSQL Versions 7 Performance of historical PostgreSQL releases 8 Choosing a version to deploy 9 Upgrading to a newer major version 9 Upgrades to PostgreSQL 8.3+ from earlier ones 10 Minor version upgrades 11 PostgreSQL or another database? 12 PostgreSQL tools 12 PostgreSQL contrib 13 Finding contrib modules on your system 13 Installing a contrib module from source 14 Using a contrib module 15 pgfoundry 15 Additional PostgreSQL-related software 16 PostgreSQL application scaling lifecycle 16 Performance tuning as a practice 17 Summary 19 Chapter 2: Database Hardware 21 Balancing hardware spending 21 CPUs 21 Memory 22 Disks 23 RAID 24 Drive error handling 26 Hard drive reliability studies 27 Drive firmware and RAID 27 SSDs 28

3 Disk controllers 29 Hardware and Software RAID 29 Recommended disk controllers 30 Attached storage SAN and NAS 32 Reliable controller and disk setup 34 Write-back caches 34 Sources of write-back caching 35 Disk controller monitoring 36 Disabling drive write caches 37 Performance impact of write-through caching 38 Summary 39 Chapter 3: Database Hardware Benchmarking 41 CPU and memory benchmarking 41 memtest STREAM memory testing 42 STREAM and Intel vs. AMD 43 CPU benchmarking 44 Sources of slow memory and processors 45 Physical disk performance 47 Random access and I/Os Per Second 47 Sequential access and ZCAV 48 Short stroking 49 Commit rate 49 PostgreSQL test_fsync 50 INSERT rate 50 Windows commit rate 50 Disk benchmarking tools 50 hdtune 51 Short stroking tests 52 IOPS 53 Unpredictable performance and Windows 54 dd 55 bonnie++ 56 bonnie bonnie++ ZCAV 58 sysbench 60 Seek rate 61 fsync commit rate 61 Complicated disk benchmarks 62 Sample disk results 63 Disk performance expectations 65 Sources of slow disk and array performance 65 Summary 67 [ii]

4 Chapter 4: Disk Setup 69 Maximum filesystem sizes 69 Filesystem crash recovery 70 Journaling filesystems 71 Linux filesystems 72 ext2 72 ext3 73 ext4 75 XFS 75 Other Linux filesystems 77 Write barriers 77 Drive support for barriers 78 Filesystem support for barriers 79 General Linux filesystem tuning 79 Read-ahead 79 File access times 80 Read caching and swapping 81 Write cache sizing 81 I/O scheduler elevator 82 Solaris and FreeBSD filesystems 84 Solaris UFS 85 FreeBSD UFS2 86 ZFS 87 Windows filesystems 89 FAT32 89 NTFS 89 Adjusting mounting behaviour 90 Disk layout for PostgreSQL 91 Symbolic links 91 Tablespaces 91 Database directory tree 92 Temporary files 93 Disk arrays, RAID, and disk layout 94 Disk layout guidelines 96 Summary 97 Chapter 5: Memory for Database Caching 99 Memory units in the postgresql.conf 99 Increasing UNIX shared memory parameters for larger buffer sizes 100 Kernel semaphores 102 Estimating shared memory allocation 102 Inspecting the database cache 104 Installing pg_buffercache into a database 105 Database disk layout 106 [Hi]

5 Table of Con ten ts Creating a new block in a database 108 Writing dirty blocks to disk 109 Crash recovery and the buffer cache 110 Checkpoint processing basics 110 Write-ahead log and recovery processing 110 Checkpoint timing 111 Checkpoint spikes 112 Spread checkpoints 112 Database block lifecycle 113 Dirty block write paths 114 Database buffer cache versus operating system cache 114 Doubly cached data 115 Inspecting the OS cache 116 Checkpoint overhead 116 Starting size guidelines 116 Platform, version, and workload limitations 117 Analyzing buffer cache contents Inspection of the buffer cache queries Top relations in the cache 119 Summary by usage count 120 Buffer contents summary, with percentages 120 Buffer usage count distribution 122 Using buffer cache inspection for sizing feedback 123 Summary 124 Chapter 6: Server Configuration Tuning 125 Interacting with the live configuration 125 Defaults and reset values 126 Allowed change context 126 Reloading the configuration file 127 Commented out settings 128 Server-wide settings 129 Database connections 129 listen_addresses 129 max_connections 130 Shared memory 131 shared_buffers 131 Free space map (FSM) settings 131 Logging 132 log_line_prefix 132 log_statement 133 log_min_duration_statement 133 Vacuuming and statistics 134 autovacuum 134 Enabling autovacuum on older versions 135 [iv]

6 maintainance_work_mem 135 default_statistics_target 136 Checkpoints 136 checkpoint_segments 137 checkpoint_timeout 138 checkpoint_completion_target 138 WAL settings 138 wal_buffers 138 wal_sync_method 139 PITR and WAL Replication 140 Per-client settings 140 effective_cache_size 141 synchronous_commit 141 work_mem 142 random_page_cost 143 constraint_exclusion 143 Tunables to avoid 143 fsync 143 full_page_writes 144 commit_delay and commit_siblings 144 max_prepared_transactions 144 Query enable parameters 145 New server tuning 145 Dedicated server guidelines 145 Shared server guidelines 146 pgtune 147 Summary 147 Chapter 7: Routine Maintenance 149 Transaction visibility with multiversion concurrency control 149 Visibility computation internals 149 Updates 150 Row lock conflicts 152 Serialization 154 Deletions 154 Advantages of MVCC 155 Disadvantages of MVCC 156 Transaction ID wraparound 156 Vacuum 158 Vacuum Implementation 158 Regular vacuum 158 Returning free disk space 159 Full vacuum 159 HOT 160 Cost-based vacuuming 160

7 autovacuum 162 autovacuum logging 163 autovacuum monitoring 163 autovacuum triggering 164 Per-table adjustments 165 Common vacuum and autovacuum problems 167 autovacuum is running even though it was turned off 167 autovacuum is constantly running 167 Out of memory errors 168 Not keeping up on a busy server 168 autovacuum is too disruptive 168 Long running transactions 169 Free Space Map exhaustion 169 Recovering from major problems 170 Autoanalyze 171 Index bloat 171 Measuring index bloat 172 Detailed data and index page monitoring 174 Monitoring query logs 175 Basic PostgreSQL log setup 175 Log collection 176 log_line_prefix 176 Multi-line queries 177 Using syslog for log messages 177 CSV logging 178 Logging difficult queries 179 auto_explain 180 Log file analysis 181 Normalized query fingerprints 181 pg_stat_statements 182 pgfouine 183 PQA 186 EPQA 186 pgsi 186 mk-query-digest 186 Summary 187 Chapter 8: Database Benchmarking 189 pgbench default tests 189 Table definition 189 Scale detection 190 Query script definition 191 Configuring the database server for pgbench 193 Sample server configuration 193 Running pgbench manually 194 Graphing results with pgbench-tools 195 [Vi]

8 Configuring pgbench-tools Customizing for 8.3 Sample pgbench test results SELECT-only test TPC-B-like test Latency analysis Sources for bad results and variation Developer PostgreSQL builds Worker threads and pgbench program limitations pgbench custom tests Insert speed test Transaction Processing Performance Council benchmarks Summary Chapter 9: Database Indexing Indexing example walkthrough Measuring query disk and index block statistics Running the example Sample data setup Simple index lookups Full table scans Index creation Lookup with an inefficient index Combining indexes Switching from indexed to sequential scans Planning for plan changes Clustering against an index Explain with buffer counts Index creation and maintenance Unique indexes Concurrent index creation Clustering an index Fill factor Reindexing Index types B-tree Text operator classes Hash GIN GiST Advanced index use Multicolumn indexes Indexes for sorting r viii

9 Partial indexes 229 Expression-based indexes 229 Indexing for full-text search 230 Summary 231 Chapter 10: Query Optimization 233 Sample data sets 233 Pagila 234 Dell Store EXPLAIN basics 236 Timing overhead 236 Hot and cold cache behavior 237 Clearing the cache 237 Query plan node structure 239 Basic cost computation 240 Estimated costs and real world costs 242 Explain analysis tools 242 Visual explain 242 Verbose output 243 Machine readable explain output 243 Plan analysis tools 244 Assembling row sets 245 Tuple id 245 Object id 246 Sequential scan 246 Index scan 247 Bitmap heap and index scans 247 Processing nodes 249 Sort 249 Limit 250 Offsets 251 Aggregate 252 HashAggregate 252 Unique 253 WindowAgg 254 Result 254 Append 255 Group 257 Subquery Scan and Subplan 258 Subquery conversion and IN lists 258 Set operations 259 Materialize 260 CTE Scan 261 [viii]

10 Joins 262 Nested loop 262 Nested loop with inner Index Scan 263 Merge Join 264 Nested loop and Merge Join materialization 265 Hash Joins 266 Hash semi and anti joins 267 Join ordering 268 Forcing join order 268 Join removal 269 Genetic query optimizer 270 Statistics 271 Viewing and estimating with statistics 271 Statistics targets 275 Adjusting a column target 275 Distinct values 276 Difficult areas to estimate 276 Other query planning parameters 277 effective_cache_size 277 work_mem 278 constraint_exclusion 279 cursor_tuple_fraction 279 Executing other statement types 280 Improving queries 280 Optimizing for fully cached data sets 281 Testing for query equivalence 281 Disabling optimizer features 282 Working around optimizer bugs 287 Avoiding plan restructuring with OFFSET 287 External trouble spots 290 SQL Limitations 291 Numbering rows in SQL 291 Using Window functions for numbering 292 Using Window functions for cumulatives 293 Summary 294 Chapter 11: Database Activity and Statistics 297 Statistics views 297 Cumulative and live views 299 Table statistics 300 Table I/O 302 Index statistics 303 Index I/O 305 [ix]

11 Database wide totals 305 Connections and activity 306 Locks 307 Virtual transactions 307 Decoding lock information 309 Transaction lock waits 312 Table lock waits 313 Logging lock information 314 Deadlocks 314 Disk usage 315 Buffer, background writer, and checkpoint activity 318 Saving pg_stat_bgwriter snapshots 319 Tuning using background writer statistics 322 Summary 324 Chapter 12: Monitoring and Trending 325 UNIX monitoring tools 325 Sample setup 325 vmstat 326 iostat 329 iotop for Linux 331 Examples of good performance 332 Overloaded system samples 335 top 338 Solaris top replacements 340 htop for Linux 340 sysstat and sar 340 Enabling sysstat and its optional features 342 Graphing with ksar 343 Windows monitoring tools 343 Task Manager 343 Sysintemals tools 344 Windows System Monitor 344 Saving Windows System Monitor data 345 Trending software 346 Types of monitoring and trending software 346 Storing historical trend data 347 Nagios 347 Nagios and PostgreSQL 348 Nagios and Windows 349 Cacti 349 Cacti and PostgreSQL 350 Cacti and Windows 350 Munin 350 [x]

12 Other trending packages 350 pgstatspack 351 Zenoss 351 Hyperic HQ 352 Reconnoiter 352 Staplr 353 SNMP tools 353 Summary 353 Chapter 13: Pooling and Caching 355 Connection pooling 355 Pooling connection counts 356 pgpool-ll 357 pgpool-ll load balancing for replication scaling 357 pgbouncer 358 Application server pooling 359 Database caching 359 memcached 360 pgmemcache 360 Summary 361 Chapter 14: Scaling with Replication 363 Hot Standby 363 Terminology 364 Setting up WAL shipping 365 Streaming Replication 366 Tuning Hot Standby 366 Replication queue managers 367 Slony 368 Londiste 369 Read scaling with replication queue software 369 Special application requirements 369 Bucardo 370 pgpool-ll 370 Other interesting replication projects 371 Summary 372 Chapter 15: Partitioning Data 375 Table range partitioning 375 Determining a key field to partition over 376 Sizing the partitions 377 List partitioning 377 Creating the partitions 378 Redirecting INSERT statements to the partitions 379 Dynamic trigger functions 380 [xi]

13 Partition rules 381 Empty partition query plans 382 Date change update trigger 382 Live migration of a partitioned table 383 Partitioned queries 386 Creating new partitions 389 Scheduled creation 389 Dynamic creation 389 Partitioning advantages 390 Common partitioning mistakes 390 Horizontal partitioning with PL/Proxy 391 Hash generation 392 Scaling with PL/Proxy 393 Sharding 394 Scaling with GridSQL 395 Summary 396 Chapter 16: Avoiding Common Problems 399 Bulk loading 399 Loading methods 399 External loading programs 400 Tuning for bulk loads 401 Skipping WAL acceleration 402 Recreating indexes and adding constraints 402 Parallel restore 403 Post load cleanup 403 Common performance issues 404 Counting rows 404 Unexplained writes 405 Slow function and prepared statement execution 406 PL/pgSQL benchmarking 407 High foreign key overhead 408 Trigger memory use 409 Heavy statistics collector overhead 409 Targeted statistics resets 410 Materialized views 410 Profiling the database 411 gprof 411 OProfile 411 Visual Studio 411 DTrace 412 DTrace on FreeBSD 412 Linux SystemTap emulation of DTrace 412 [xii]

14 Performance related features by version 413 Aggressive PostgreSQL version upgrades Replication 419 Queries and EXPLAIN 420 Database development 421 Configuration and monitoring 422 Tools 423 Internals 423 Summary 424 Index 427 [ xiii ]