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Commitc4ab7da

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Avoid needless large memcpys in libpq socket writing
Until now, when calling pq_putmessage to write new data to a libpqsocket, all writes are copied into a buffer and that buffer gets flushedwhen full to avoid having to perform small writes to the socket.There are cases where we must write large amounts of data to the socket,sometimes larger than the size of the buffer. In this case, it'swasteful to memcpy this data into the buffer and flush it out, instead,we can send it directly from the memory location that the data is alreadystored in.Here we adjust internal_putbytes() so that after having just flushed thebuffer to the socket, if the remaining bytes to send is as big or biggerthan the buffer size, we just send directly rather than needlesslycopying into the PqSendBuffer buffer first.Examples of operations that write large amounts of data in one messageare; outputting large tuples with SELECT or COPY TO STDOUT andpg_basebackup.Author: Melih MutluReviewed-by: Heikki LinnakangasReviewed-by: Jelte Fennema-NioReviewed-by: David RowleyReviewed-by: Ranier VilelaReviewed-by: Andres FreundDiscussion:https://postgr.es/m/CAGPVpCR15nosj0f6xe-c2h477zFR88q12e6WjEoEZc8ZYkTh3Q@mail.gmail.com
1 parenta97bbe1 commitc4ab7da

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1 file changed

+53
-21
lines changed

1 file changed

+53
-21
lines changed

‎src/backend/libpq/pqcomm.c

Lines changed: 53 additions & 21 deletions
Original file line numberDiff line numberDiff line change
@@ -120,8 +120,8 @@ static List *sock_paths = NIL;
120120

121121
staticchar*PqSendBuffer;
122122
staticintPqSendBufferSize;/* Size send buffer */
123-
staticintPqSendPointer;/* Next index to store a byte in PqSendBuffer */
124-
staticintPqSendStart;/* Next index to send a byte in PqSendBuffer */
123+
staticsize_tPqSendPointer;/* Next index to store a byte in PqSendBuffer */
124+
staticsize_tPqSendStart;/* Next index to send a byte in PqSendBuffer */
125125

126126
staticcharPqRecvBuffer[PQ_RECV_BUFFER_SIZE];
127127
staticintPqRecvPointer;/* Next index to read a byte from PqRecvBuffer */
@@ -143,8 +143,10 @@ static intsocket_flush_if_writable(void);
143143
staticboolsocket_is_send_pending(void);
144144
staticintsocket_putmessage(charmsgtype,constchar*s,size_tlen);
145145
staticvoidsocket_putmessage_noblock(charmsgtype,constchar*s,size_tlen);
146-
staticintinternal_putbytes(constchar*s,size_tlen);
147-
staticintinternal_flush(void);
146+
staticinlineintinternal_putbytes(constchar*s,size_tlen);
147+
staticinlineintinternal_flush(void);
148+
staticpg_noinlineintinternal_flush_buffer(constchar*buf,size_t*start,
149+
size_t*end);
148150

149151
staticintLock_AF_UNIX(constchar*unixSocketDir,constchar*unixSocketPath);
150152
staticintSetup_AF_UNIX(constchar*sock_path);
@@ -1268,11 +1270,9 @@ pq_getmessage(StringInfo s, int maxlen)
12681270
}
12691271

12701272

1271-
staticint
1273+
staticinlineint
12721274
internal_putbytes(constchar*s,size_tlen)
12731275
{
1274-
size_tamount;
1275-
12761276
while (len>0)
12771277
{
12781278
/* If buffer is full, then flush it out */
@@ -1282,14 +1282,33 @@ internal_putbytes(const char *s, size_t len)
12821282
if (internal_flush())
12831283
returnEOF;
12841284
}
1285-
amount=PqSendBufferSize-PqSendPointer;
1286-
if (amount>len)
1287-
amount=len;
1288-
memcpy(PqSendBuffer+PqSendPointer,s,amount);
1289-
PqSendPointer+=amount;
1290-
s+=amount;
1291-
len-=amount;
1285+
1286+
/*
1287+
* If the buffer is empty and data length is larger than the buffer
1288+
* size, send it without buffering. Otherwise, copy as much data as
1289+
* possible into the buffer.
1290+
*/
1291+
if (len >=PqSendBufferSize&&PqSendStart==PqSendPointer)
1292+
{
1293+
size_tstart=0;
1294+
1295+
socket_set_nonblocking(false);
1296+
if (internal_flush_buffer(s,&start,&len))
1297+
returnEOF;
1298+
}
1299+
else
1300+
{
1301+
size_tamount=PqSendBufferSize-PqSendPointer;
1302+
1303+
if (amount>len)
1304+
amount=len;
1305+
memcpy(PqSendBuffer+PqSendPointer,s,amount);
1306+
PqSendPointer+=amount;
1307+
s+=amount;
1308+
len-=amount;
1309+
}
12921310
}
1311+
12931312
return0;
12941313
}
12951314

@@ -1321,19 +1340,32 @@ socket_flush(void)
13211340
* and the socket is in non-blocking mode), or EOF if trouble.
13221341
* --------------------------------
13231342
*/
1324-
staticint
1343+
staticinlineint
13251344
internal_flush(void)
1345+
{
1346+
returninternal_flush_buffer(PqSendBuffer,&PqSendStart,&PqSendPointer);
1347+
}
1348+
1349+
/* --------------------------------
1350+
*internal_flush_buffer - flush the given buffer content
1351+
*
1352+
* Returns 0 if OK (meaning everything was sent, or operation would block
1353+
* and the socket is in non-blocking mode), or EOF if trouble.
1354+
* --------------------------------
1355+
*/
1356+
staticpg_noinlineint
1357+
internal_flush_buffer(constchar*buf,size_t*start,size_t*end)
13261358
{
13271359
staticintlast_reported_send_errno=0;
13281360

1329-
char*bufptr=PqSendBuffer+PqSendStart;
1330-
char*bufend=PqSendBuffer+PqSendPointer;
1361+
constchar*bufptr=buf+*start;
1362+
constchar*bufend=buf+*end;
13311363

13321364
while (bufptr<bufend)
13331365
{
13341366
intr;
13351367

1336-
r=secure_write(MyProcPort,bufptr,bufend-bufptr);
1368+
r=secure_write(MyProcPort,(char*)bufptr,bufend-bufptr);
13371369

13381370
if (r <=0)
13391371
{
@@ -1373,18 +1405,18 @@ internal_flush(void)
13731405
* flag that'll cause the next CHECK_FOR_INTERRUPTS to terminate
13741406
* the connection.
13751407
*/
1376-
PqSendStart=PqSendPointer=0;
1408+
*start=*end=0;
13771409
ClientConnectionLost=1;
13781410
InterruptPending=1;
13791411
returnEOF;
13801412
}
13811413

13821414
last_reported_send_errno=0;/* reset after any successful send */
13831415
bufptr+=r;
1384-
PqSendStart+=r;
1416+
*start+=r;
13851417
}
13861418

1387-
PqSendStart=PqSendPointer=0;
1419+
*start=*end=0;
13881420
return0;
13891421
}
13901422

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