Problem: Pipeline sync might deadlock #823
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**Deadlock call stack:** ``` %0 0x0000787ac168fe16 in select () from target:/lib/x86_64-linux-gnu/libc.so.6 %1 0x000057db30f718ad in pgsql_sync_pipeline (pgsql=pgsql@entry=0x7ffc8ce1f9c8) at pgsql.c:1979 %2 0x000057db30f5bc2c in stream_apply_file (context=context@entry=0x7ffc8ce1d880) at ld_apply.c:657 %3 0x000057db30f5c495 in stream_apply_catchup (specs=specs@entry=0x7ffc8d030050) at ld_apply.c:112 %4 0x000057db30f549d2 in follow_start_catchup (specs=0x7ffc8d030050) at follow.c:809 %5 0x000057db30f54baa in follow_start_subprocess (specs=specs@entry=0x7ffc8d030050, % subprocess=subprocess@entry=0x7ffc8d138da8) at follow.c:860 %6 0x000057db30f55383 in follow_prepare_mode_switch (streamSpecs=streamSpecs@entry=0x7ffc8d030050, % previousMode=previousMode@entry=STREAM_MODE_CATCHUP, currentMode=currentMode@entry=STREAM_MODE_REPLAY) at follow.c:488 %7 0x000057db30f55a0b in follow_main_loop (copySpecs=copySpecs@entry=0x7ffc8d13bd50, % streamSpecs=streamSpecs@entry=0x7ffc8d030050) at follow.c:340 %8 0x000057db30f37cbb in cli_follow (argc=<optimized out>, argv=<optimized out>) at cli_clone_follow.c:464 %9 0x000057db30f8a17a in commandline_run (command=command@entry=0x7ffc8d24f0d0, argc=0, argc@entry=4, argv=0x7ffc8d24f248, % argv@entry=0x7ffc8d24f228) at /usr/src/pgcopydb/src/bin/pgcopydb/../lib/subcommands.c/commandline.c:71 %10 0x000057db30f36cf0 in main (argc=4, argv=0x7ffc8d24f228) at main.c:142 ``` **Root cause:** PQpipelineSync might clear select read condition because it might read the data from server. Code path:(PQpipelineSync->pqPipelineSyncInternal->pqFlush->pqSendSome->pqReadData) **Solution:** Get rid of select call and read results in a blocking mode. It also reduces CPU utilization as the function never pools. Along with fixing the deadlock, this commit also fixes the following, 1) Use after free while dealing with PGresult 2) Handle notifications while readings results [1] https://github.com/postgres/postgres/blob/fd49e8f32325c675d9bb6e26fcdbe9754249932f/src/interfaces/libpq/fe-misc.c#L856-L926 Fixes timescale/team-data-onboarding#149 Signed-off-by: Arunprasad Rajkumar <ar.arunprasad@gmail.com>
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Fixes #794 |
dimitri
approved these changes
Jun 24, 2024
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Deadlock call stack:
Root cause:
PQpipelineSync might clear select read condition because it might read the data from server.
Code path:(PQpipelineSync->pqPipelineSyncInternal->pqFlush->pqSendSome->pqReadData)
Solution:
Get rid of select call and read results in a blocking mode. It also reduces CPU utilization as the function never pools.
Along with fixing the deadlock, this commit also fixes the following,