postgresql的相关服务端问题及解决方法
Caused by: org.postgresql.util.PSQLException: ERROR: connection to the remote node 10.20.30.195:5435 failed with the following error: could not fork new process for connection: Resource temporarily unavailable
服务器资源不足，可能是内存、linux共享内存段配置太低、overcommit超了或进程数。如：
CommitLimit: 199412136 kB Committed_AS: 199564684 kB # 接近limit时就可能提示资源临时不可用
### Cause: org.postgresql.util.PSQLException: ERROR: out of memory Detail: Failed on request of size 40364 in memory context "CacheMemoryContext". Where: while executing command on 10.20.30.217:5437 ; SQL []; ERROR: out of memory
内存不足、linux共享内存段配置太低、overcommit超了。可以查询pg_shmem_allocations查看当前的实际内存分配情况：
select * from pg_shmem_allocations; name |off |size |allocated_size| -----------------------------------+-----------+-----------+--------------+ Buffer Blocks | 1084544896|60615032832| 60615032832| Buffer Descriptors | 137435008| 947109888| 947109888| <anonymous> | | 572226944| 572226944| DirtyPageQueue |63185582464| 295971840| 295971840| Buffer IO Locks |61699577728| 236777472| 236777472| PageWriter Data |62823015552| 177584504| 177584512| Checkpointer Data |62645432320| 177583168| 177583232| Checkpoint BufferIds |61936355200| 147985920| 147985920| Pagewriter BufferIds |63000600064| 147985920| 147985920| XLOG Ctl | 309504| 134358672| 134358784| |63514032256| 75728768| 75728768| CandidateBuffers |63148585984| 29597184| 29597184| BatchFileHead |63481561216| 13508608| 13508608| CandidateFreeMap |63178183168| 7399296| 7399296| Backend Activity Buffer |62641214720| 2152448| 2152448| Xact | 134668672| 2116320| 2116352| KnownAssignedXids |62638078976| 1580280| 1580288| Prepared Transaction Table |62644056704| 1056016| 1056128| Backend Status Array |62640054400| 891248| 891264| Backend SSL Status Buffer |62643367168| 689456| 689536| KnownAssignedXidsValid |62639659264| 395070| 395136| Subtrans | 136918784| 267008| 267008| Shared Buffer Lookup Table |62084341120| 263000| 263040| ProcSignal |62645297664| 134536| 134656| Backend Client Host Name Buffer |62641080192| 134528| 134528| Backend Application Name Buffer |62640945664| 134528| 134528| CommitTs | 136785024| 133568| 133632| MultiXactMember | 137252608| 133568| 133632| Serial |62632431360| 133568| 133632| shmInvalBuffer |62645148800| 132056| 132096| Notify |63495199744| 66816| 66816| MultiXactOffset | 137185792| 66816| 66816| lt_stat_activity |63496779392| 48800| 48896| Shared MultiXact State | 137386240| 48676| 48768| Async Queue Control |63495158016| 41612| 41728| Background Worker Data |62645112832| 35856| 35968| PROCLOCK hash |62482482432| 33624| 33664| PREDICATELOCK hash |62540721280| 33624| 33664| SingleFlushState |63495086848| 32767| 32768| BTree Vacuum State |63495132288| 24948| 24960| Proc Array |62638054528| 24352| 24448| PREDICATELOCKTARGET hash |62517836032| 17240| 17280| LOCK hash |62447690112| 17240| 17280| PMSignalState |62645280896| 16668| 16768| SingleFileHead |63495070464| 16384| 16384| AutoVacuum Data |63495119616| 5368| 5376| Fast Path Strong Relation Lock Data|62517831808| 4100| 4224| CkptRedoState |63481554304| 3840| 3840| pg_show_plans hash |63496828416| 2904| 2944| pg_stat_statements hash |63495270912| 2904| 2944| SERIALIZABLEXID hash |62615371648| 2904| 2944| ReplicationSlot Ctl |63495124992| 2480| 2560| BatchFileCxts |63481558784| 2416| 2432| Wal Receiver Ctl |63495129344| 2248| 2304| Wal Sender Ctl |63495128192| 1040| 1152| Sync Scan Locations List |63495157248| 656| 768| DW Batch Data |63481558144| 552| 640| DW Single Data |63495069824| 552| 640| ReplicationOriginState |63495127552| 568| 640| Logical Replication Launcher Data |63495131648| 424| 512| Control File | 134668288| 312| 384| pg_show_plans |63496828288| 16| 128| FinishedSerializableTransactions |62632431232| 16| 128| Proc Header |62632565120| 112| 128| CommitTs shared | 136918656| 32| 128| OldSnapshotControlData |63495132160| 68| 128| PredXactList |62605160448| 88| 128| RWConflictPool |62617843840| 24| 128| Buffer Strategy Status |62447689984| 28| 128| SerialControlData |62632564992| 12| 128| pg_stat_statements |63495270784| 48| 128| Cluster Encryption Key |63495270656| 18| 128|
lightdb 23.1版本开始，在lightdb.log启动日志中包含了实际申请的共享内存大小，如下：
[lightdb@hs-10-20-30-199 13.8-23.1]$ lt_ctl -D test_incre restart
waiting for server to shut down.................. done
server stopped
2023-05-12 21:37:01.398108T,,,,,postmaster,,00000,2023-05-12 21:37:01 CST,0,11193,LOG: LightDB autoprewarm: prewarm dbnum=0
2023-05-12 21:37:01.400707T,,,,,postmaster,,00000,2023-05-12 21:37:01 CST,0,11193,INFO: invoking IpcMemoryCreate(size=62444929024)
waiting for server to start....2023-05-12 21:37:02.261923T,,,,,postmaster,,00000,2023-05-12 21:37:01 CST,0,11193,LOG: redirecting log output to logging collector process
2023-05-12 21:37:02.261923T,,,,,postmaster,,00000,2023-05-12 21:37:01 CST,0,11193,HINT: Future log output will appear in directory "log".
done
server started
2021-12-31 14:03:21.441691C [unknown] lightdb@findptdis 10.20.30.193(12146) client backend SELECT 57P01[2021-12-31 13:45:14 UTC] 0 [71437] ERROR: terminating connection due to administrator command
服务器进程被正常或异常重启或停止或kill，包括具体的某个backend进程。
2PC未成功，回滚响应未收到，第二次重复回滚导致。
