PostgreSQL 10.0 preview 功能增强 - SQL执行剩余时间 - 垃圾回收过程可视pg_stat_progress_vacuum

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目前PostgreSQL增加了对VACUUM的可视监控(目前涵盖了autovacuum与手工的vacuum命令,但是不涵盖VACUUM FULL),将来还会加入更多的progress动态视图,方便用户了解LONG SQL或者任务的执行情况。


可以了解每个vacuum worker工作进程在工作过程中,扫描了多少HEAP PAGE, 回收了多少PAGE,index的vacuum关卡次数(每个关卡的大小取决于maintenance_work_mem可以存储的heap tuple数量)。

Table 28.21. pg_stat_progress_vacuum View

Column Type Description
pid integer Process ID of backend.
datid oid OID of the database to which this backend is connected.
datname name Name of the database to which this backend is connected.
relid oid OID of the table being vacuumed.
phase text Current processing phase of vacuum. See Table 28.22.
heap_blks_total bigint Total number of heap blocks in the table. This number is reported as of the beginning of the scan; blocks added later will not be (and need not be) visited by this VACUUM.
heap_blks_scanned bigint Number of heap blocks scanned. Because the visibility map is used to optimize scans, some blocks will be skipped without inspection; skipped blocks are included in this total, so that this number will eventually become equal to heap_blks_total when the vacuum is complete. This counter only advances when the phase is scanning heap.
heap_blks_vacuumed bigint Number of heap blocks vacuumed. Unless the table has no indexes, this counter only advances when the phase is vacuuming heap. Blocks that contain no dead tuples are skipped, so the counter may sometimes skip forward in large increments.
index_vacuum_count bigint Number of completed index vacuum cycles.
max_dead_tuples bigint Number of dead tuples that we can store before needing to perform an index vacuum cycle, based on maintenance_work_mem.
num_dead_tuples bigint Number of dead tuples collected since the last index vacuum cycle.


Table 28.22. VACUUM phases

Phase Description
initializing VACUUM is preparing to begin scanning the heap. This phase is expected to be very brief.
scanning heap VACUUM is currently scanning the heap. It will prune and defragment each page if required, and possibly perform freezing activity. The heap_blks_scanned column can be used to monitor the progress of the scan.
vacuuming indexes VACUUM is currently vacuuming the indexes. If a table has any indexes, this will happen at least once per vacuum, after the heap has been completely scanned. It may happen multiple times per vacuum if maintenance_work_mem is insufficient to store the number of dead tuples found.
vacuuming heap VACUUM is currently vacuuming the heap. Vacuuming the heap is distinct from scanning the heap, and occurs after each instance of vacuuming indexes. If heap_blks_scanned is less than heap_blks_total, the system will return to scanning the heap after this phase is completed; otherwise, it will begin cleaning up indexes after this phase is completed.
cleaning up indexes VACUUM is currently cleaning up indexes. This occurs after the heap has been completely scanned and all vacuuming of the indexes and the heap has been completed.
truncating heap VACUUM is currently truncating the heap so as to return empty pages at the end of the relation to the operating system. This occurs after cleaning up indexes.
performing final cleanup VACUUM is performing final cleanup. During this phase, VACUUM will vacuum the free space map, update statistics in pg_class, and report statistics to the statistics collector. When this phase is completed, VACUUM will end.




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