Extensible copy #2
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This is a part of making COPY format extendable. See also these past discussions: * New Copy Formats - avro/orc/parquet: https://www.postgresql.org/message-id/flat/20180210151304.fonjztsynewldfba%40gmail.com * Make COPY extendable in order to support Parquet and other formats: https://www.postgresql.org/message-id/flat/CAJ7c6TM6Bz1c3F04Cy6%2BSzuWfKmr0kU8c_3Stnvh_8BR0D6k8Q%40mail.gmail.com This doesn't change the current behavior. This just introduces CopyToRoutine, which just has function pointers of format implementation like TupleTableSlotOps, and use it for existing "text", "csv" and "binary" format implementations. Note that CopyToRoutine can't be used from extensions yet because CopySend*() aren't exported yet. Extensions can't send formatted data to a destination without CopySend*(). They will be exported by subsequent patches. Here is a benchmark result with/without this change because there was a discussion that we should care about performance regression: https://www.postgresql.org/message-id/3741749.1655952719%40sss.pgh.pa.us > I think that step 1 ought to be to convert the existing formats into > plug-ins, and demonstrate that there's no significant loss of > performance. You can see that there is no significant loss of performance: Data: Random 32 bit integers: CREATE TABLE data (int32 integer); INSERT INTO data SELECT random() * 10000 FROM generate_series(1, ${n_records}); The number of records: 100K, 1M and 10M 100K without this change: format,elapsed time (ms) text,11.002 csv,11.696 binary,11.352 100K with this change: format,elapsed time (ms) text,100000,11.562 csv,100000,11.889 binary,100000,10.825 1M without this change: format,elapsed time (ms) text,108.359 csv,114.233 binary,111.251 1M with this change: format,elapsed time (ms) text,111.269 csv,116.277 binary,104.765 10M without this change: format,elapsed time (ms) text,1090.763 csv,1136.103 binary,1137.141 10M with this change: format,elapsed time (ms) text,1082.654 csv,1196.991 binary,1069.697
This uses the handler approach like tablesample. The approach creates
an internal function that returns an internal struct. In this case,
a COPY TO handler returns a CopyToRoutine.
We will add support for custom COPY FROM format later. We'll use the
same handler for COPY TO and COPY FROM. PostgreSQL calls a COPY
TO/FROM handler with "is_from" argument. It's true for COPY FROM and
false for COPY TO:
copy_handler(true) returns CopyToRoutine
copy_handler(false) returns CopyFromRoutine (not exist yet)
We discussed that we introduce a wrapper struct for it:
typedef struct CopyRoutine
{
NodeTag type;
/* either CopyToRoutine or CopyFromRoutine */
Node *routine;
}
copy_handler(true) returns CopyRoutine with CopyToRoutine
copy_handler(false) returns CopyRoutine with CopyFromRoutine
See also: https://www.postgresql.org/message-id/flat/CAD21AoCunywHird3GaPzWe6s9JG1wzxj3Cr6vGN36DDheGjOjA%40mail.gmail.com
But I noticed that we don't need the wrapper struct. We can just
CopyToRoutine or CopyFromRoutine. Because we can distinct the returned
struct by checking its NodeTag. So I don't use the wrapper struct
approach.
It's for custom COPY TO format handlers implemented as extension. This just moves codes. This doesn't change codes except CopyDest enum values. CopyDest enum values such as COPY_FILE are conflicted CopySource enum values defined in copyfrom_internal.h. So COPY_DEST_ prefix instead of COPY_ prefix is used. For example, COPY_FILE is renamed to COPY_DEST_FILE. Note that this change isn't enough to implement a custom COPY TO format handler as extension. We'll do the followings in a subsequent commit: 1. Add an opaque space for custom COPY TO format handler 2. Export CopySendEndOfRow() to flush buffer
* Add CopyToStateData::opaque that can be used to keep data for custom COPY TO format implementation * Export CopySendEndOfRow() to flush data in CopyToStateData::fe_msgbuf * Rename CopySendEndOfRow() to CopyToStateFlush() because it's a method for CopyToState and it's used for flushing. End-of-row related codes were moved to CopyToTextSendEndOfRow().
This doesn't change the current behavior. This just introduces CopyFromRoutine, which just has function pointers of format implementation like TupleTableSlotOps, and use it for existing "text", "csv" and "binary" format implementations. Note that CopyFromRoutine can't be used from extensions yet because CopyRead*() aren't exported yet. Extensions can't read data from a source without CopyRead*(). They will be exported by subsequent patches.
We use the same approach as we used for custom COPY TO format. Now,
custom COPY format handler can return COPY TO format routines or COPY
FROM format routines based on the "is_from" argument:
copy_handler(true) returns CopyToRoutine
copy_handler(false) returns CopyFromRoutine
It's for custom COPY FROM format handlers implemented as extension. This just moves codes. This doesn't change codes except CopySource enum values. CopySource enum values changes aren't required but I did like I did for CopyDest enum values. I changed COPY_ prefix to COPY_SOURCE_ prefix. For example, COPY_FILE to COPY_SOURCE_FILE. Note that this change isn't enough to implement a custom COPY FROM format handler as extension. We'll do the followings in a subsequent commit: 1. Add an opaque space for custom COPY FROM format handler 2. Export CopyReadBinaryData() to read the next data
* Add CopyFromStateData::opaque that can be used to keep data for custom COPY From format implementation * Export CopyReadBinaryData() to read the next data * Rename CopyReadBinaryData() to CopyFromStateRead() because it's a method for CopyFromState and "BinaryData" is redundant.
Signed-off-by: Zhao Junwang <[email protected]>
Signed-off-by: Zhao Junwang <[email protected]>
zhjwpku
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Jul 28, 2024
1. TruncateMultiXact() performs the SLRU truncations in a critical
section. Deleting the SLRU segments calls ForwardSyncRequest(), which
will try to compact the request queue if it's full
(CompactCheckpointerRequestQueue()). That in turn allocates memory,
which is not allowed in a critical section. Backtrace:
TRAP: failed Assert("CritSectionCount == 0 || (context)->allowInCritSection"), File: "../src/backend/utils/mmgr/mcxt.c", Line: 1353, PID: 920981
postgres: autovacuum worker template0(ExceptionalCondition+0x6e)[0x560a501e866e]
postgres: autovacuum worker template0(+0x5dce3d)[0x560a50217e3d]
postgres: autovacuum worker template0(ForwardSyncRequest+0x8e)[0x560a4ffec95e]
postgres: autovacuum worker template0(RegisterSyncRequest+0x2b)[0x560a50091eeb]
postgres: autovacuum worker template0(+0x187b0a)[0x560a4fdc2b0a]
postgres: autovacuum worker template0(SlruDeleteSegment+0x101)[0x560a4fdc2ab1]
postgres: autovacuum worker template0(TruncateMultiXact+0x2fb)[0x560a4fdbde1b]
postgres: autovacuum worker template0(vac_update_datfrozenxid+0x4b3)[0x560a4febd2f3]
postgres: autovacuum worker template0(+0x3adf66)[0x560a4ffe8f66]
postgres: autovacuum worker template0(AutoVacWorkerMain+0x3ed)[0x560a4ffe7c2d]
postgres: autovacuum worker template0(+0x3b1ead)[0x560a4ffecead]
postgres: autovacuum worker template0(+0x3b620e)[0x560a4fff120e]
postgres: autovacuum worker template0(+0x3b3fbb)[0x560a4ffeefbb]
postgres: autovacuum worker template0(+0x2f724e)[0x560a4ff3224e]
/lib/x86_64-linux-gnu/libc.so.6(+0x27c8a)[0x7f62cc642c8a]
/lib/x86_64-linux-gnu/libc.so.6(__libc_start_main+0x85)[0x7f62cc642d45]
postgres: autovacuum worker template0(_start+0x21)[0x560a4fd16f31]
To fix, bail out in CompactCheckpointerRequestQueue() without doing
anything, if it's called in a critical section. That covers the above
call path, as well as any other similar cases where
RegisterSyncRequest might be called in a critical section.
2. After fixing that, another problem became apparent: Autovacuum
process doing that truncation can deadlock with the checkpointer
process. TruncateMultiXact() sets "MyProc->delayChkptFlags |=
DELAY_CHKPT_START". If the sync request queue is full and cannot be
compacted, the process will repeatedly sleep and retry, until there is
room in the queue. However, if the checkpointer is trying to start a
checkpoint at the same time, and is waiting for the DELAY_CHKPT_START
processes to finish, the queue will never shrink.
More concretely, the autovacuum process is stuck here:
#0 0x00007fc934926dc3 in epoll_wait () from /lib/x86_64-linux-gnu/libc.so.6
#1 0x000056220b24348b in WaitEventSetWaitBlock (set=0x56220c2e4b50, occurred_events=0x7ffe7856d040, nevents=1, cur_timeout=<optimized out>) at ../src/backend/storage/ipc/latch.c:1570
#2 WaitEventSetWait (set=0x56220c2e4b50, timeout=timeout@entry=10, occurred_events=<optimized out>, occurred_events@entry=0x7ffe7856d040, nevents=nevents@entry=1,
wait_event_info=wait_event_info@entry=150994949) at ../src/backend/storage/ipc/latch.c:1516
postgres#3 0x000056220b243224 in WaitLatch (latch=<optimized out>, latch@entry=0x0, wakeEvents=wakeEvents@entry=40, timeout=timeout@entry=10, wait_event_info=wait_event_info@entry=150994949)
at ../src/backend/storage/ipc/latch.c:538
postgres#4 0x000056220b26cf46 in RegisterSyncRequest (ftag=ftag@entry=0x7ffe7856d0a0, type=type@entry=SYNC_FORGET_REQUEST, retryOnError=true) at ../src/backend/storage/sync/sync.c:614
postgres#5 0x000056220af9db0a in SlruInternalDeleteSegment (ctl=ctl@entry=0x56220b7beb60 <MultiXactMemberCtlData>, segno=segno@entry=11350) at ../src/backend/access/transam/slru.c:1495
postgres#6 0x000056220af9dab1 in SlruDeleteSegment (ctl=ctl@entry=0x56220b7beb60 <MultiXactMemberCtlData>, segno=segno@entry=11350) at ../src/backend/access/transam/slru.c:1566
postgres#7 0x000056220af98e1b in PerformMembersTruncation (oldestOffset=<optimized out>, newOldestOffset=<optimized out>) at ../src/backend/access/transam/multixact.c:3006
postgres#8 TruncateMultiXact (newOldestMulti=newOldestMulti@entry=3221225472, newOldestMultiDB=newOldestMultiDB@entry=4) at ../src/backend/access/transam/multixact.c:3201
postgres#9 0x000056220b098303 in vac_truncate_clog (frozenXID=749, minMulti=<optimized out>, lastSaneFrozenXid=749, lastSaneMinMulti=3221225472) at ../src/backend/commands/vacuum.c:1917
postgres#10 vac_update_datfrozenxid () at ../src/backend/commands/vacuum.c:1760
postgres#11 0x000056220b1c3f76 in do_autovacuum () at ../src/backend/postmaster/autovacuum.c:2550
postgres#12 0x000056220b1c2c3d in AutoVacWorkerMain (startup_data=<optimized out>, startup_data_len=<optimized out>) at ../src/backend/postmaster/autovacuum.c:1569
and the checkpointer is stuck here:
#0 0x00007fc9348ebf93 in clock_nanosleep () from /lib/x86_64-linux-gnu/libc.so.6
#1 0x00007fc9348fe353 in nanosleep () from /lib/x86_64-linux-gnu/libc.so.6
#2 0x000056220b40ecb4 in pg_usleep (microsec=microsec@entry=10000) at ../src/port/pgsleep.c:50
postgres#3 0x000056220afb43c3 in CreateCheckPoint (flags=flags@entry=108) at ../src/backend/access/transam/xlog.c:7098
postgres#4 0x000056220b1c6e86 in CheckpointerMain (startup_data=<optimized out>, startup_data_len=<optimized out>) at ../src/backend/postmaster/checkpointer.c:464
To fix, add AbsorbSyncRequests() to the loops where the checkpointer
waits for DELAY_CHKPT_START or DELAY_CHKPT_COMPLETE operations to
finish.
Backpatch to v14. Before that, SLRU deletion didn't call
RegisterSyncRequest, which avoided this failure. I'm not sure if there
are other similar scenarios on older versions, but we haven't had
any such reports.
Discussion: https://www.postgresql.org/message-id/[email protected]
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