mirror of
https://github.com/postgres/postgres.git
synced 2026-04-14 21:47:31 -04:00
999dec9ec6
When a backend attempts to start a read IO and finds the first buffer already has I/O in progress, previously it waited for that I/O to complete before initiating reads for any of the subsequent buffers. Although it must wait for the I/O to finish when acquiring the buffer, there's no reason for it to wait when setting up the read operation. Waiting at this point prevents starting I/O on subsequent buffers and can significantly reduce concurrency. This matters in two workloads: 1) When multiple backends scan the same relation concurrently. 2) When a single backend requests the same block multiple times within the readahead distance. Waiting each time an in-progress read is encountered effectively degenerates the access pattern into synchronous I/O. To fix this, when encountering an already in-progress IO for the head buffer, the wait reference is now recorded and waiting is deferred until WaitReadBuffers(), when the buffer actually needs to be acquired. In rare cases, a backend may still need to wait synchronously at IO start time: If another backend has set BM_IO_IN_PROGRESS on the buffer but has not yet set the wait reference. Such windows should be brief and uncommon. Author: Melanie Plageman <melanieplageman@gmail.com> Author: Andres Freund <andres@anarazel.de> Reviewed-by: Andres Freund <andres@anarazel.de> Reviewed-by: Melanie Plageman <melanieplageman@gmail.com> Reviewed-by: Nazir Bilal Yavuz <byavuz81@gmail.com> Discussion: https://postgr.es/m/flat/zljergweqti7x67lg5ije2rzjusie37nslsnkjkkby4laqqbfw%403p3zu522yykv |
||
|---|---|---|
| .. | ||
| access | ||
| archive | ||
| backup | ||
| bootstrap | ||
| catalog | ||
| commands | ||
| common | ||
| datatype | ||
| executor | ||
| fe_utils | ||
| foreign | ||
| jit | ||
| lib | ||
| libpq | ||
| mb | ||
| nodes | ||
| optimizer | ||
| parser | ||
| partitioning | ||
| pch | ||
| port | ||
| portability | ||
| postmaster | ||
| regex | ||
| replication | ||
| rewrite | ||
| snowball | ||
| statistics | ||
| storage | ||
| tcop | ||
| tsearch | ||
| utils | ||
| .gitignore | ||
| c.h | ||
| fmgr.h | ||
| funcapi.h | ||
| getopt_long.h | ||
| Makefile | ||
| meson.build | ||
| miscadmin.h | ||
| pg_config.h.in | ||
| pg_config_manual.h | ||
| pg_getopt.h | ||
| pg_trace.h | ||
| pgstat.h | ||
| pgtar.h | ||
| pgtime.h | ||
| port.h | ||
| postgres.h | ||
| postgres_ext.h | ||
| postgres_fe.h | ||
| varatt.h | ||
| windowapi.h | ||