*** a/src/backend/postmaster/syslogger.c
--- b/src/backend/postmaster/syslogger.c
***************
*** 93,101 **** static char *last_file_name = NULL;
  static char *last_csv_file_name = NULL;
  
  /*
!  * Buffers for saving partial messages from different backends. We don't expect
!  * that there will be very many outstanding at one time, so 20 seems plenty of
!  * leeway. If this array gets full we won't lose messages, but we will lose
   * the protocol protection against them being partially written or interleaved.
   *
   * An inactive buffer has pid == 0 and undefined contents of data.
--- 93,108 ----
  static char *last_csv_file_name = NULL;
  
  /*
!  * Buffers for saving partial messages from different backends.
!  *
!  * Under heavy load we can get quite a few of them, so we stripe them across
!  * an array based on the mod of the pid, which seem an adequate hash function
!  * for pids. We do this rather then just keeping a one-dimensional array so
!  * we don't have to probe too many slots for any given pid.
!  * 20 stripes of 20 slots each seems likely to be adequate leeway, but if there
!  * are lots of overruns we might need to increase CHUNK_STRIPES a bit, or look
!  * at some alternative scheme.
!  * If a stripe gets full we won't lose messages, but we will lose
   * the protocol protection against them being partially written or interleaved.
   *
   * An inactive buffer has pid == 0 and undefined contents of data.
***************
*** 107,113 **** typedef struct
  } save_buffer;
  
  #define CHUNK_SLOTS 20
! static save_buffer saved_chunks[CHUNK_SLOTS];
  
  /* These must be exported for EXEC_BACKEND case ... annoying */
  #ifndef WIN32
--- 114,121 ----
  } save_buffer;
  
  #define CHUNK_SLOTS 20
! #define CHUNK_STRIPES 20
! static save_buffer saved_chunks[CHUNK_STRIPES][CHUNK_SLOTS];
  
  /* These must be exported for EXEC_BACKEND case ... annoying */
  #ifndef WIN32
***************
*** 725,730 **** process_pipe_input(char *logbuffer, int *bytes_in_logbuffer)
--- 733,739 ----
  	{
  		PipeProtoHeader p;
  		int			chunklen;
+ 		int         stripe;
  
  		/* Do we have a valid header? */
  		memcpy(&p, cursor, sizeof(PipeProtoHeader));
***************
*** 743,748 **** process_pipe_input(char *logbuffer, int *bytes_in_logbuffer)
--- 752,759 ----
  			dest = (p.is_last == 'T' || p.is_last == 'F') ?
  				LOG_DESTINATION_CSVLOG : LOG_DESTINATION_STDERR;
  
+ 			stripe = p.pid % CHUNK_STRIPES;
+ 
  			if (p.is_last == 'f' || p.is_last == 'F')
  			{
  				/*
***************
*** 756,780 **** process_pipe_input(char *logbuffer, int *bytes_in_logbuffer)
  
  				for (i = 0; i < CHUNK_SLOTS; i++)
  				{
! 					if (saved_chunks[i].pid == p.pid)
  					{
  						existing_slot = i;
  						break;
  					}
! 					if (free_slot < 0 && saved_chunks[i].pid == 0)
  						free_slot = i;
  				}
  				if (existing_slot >= 0)
  				{
! 					str = &(saved_chunks[existing_slot].data);
  					appendBinaryStringInfo(str,
  										   cursor + PIPE_HEADER_SIZE,
  										   p.len);
  				}
  				else if (free_slot >= 0)
  				{
! 					saved_chunks[free_slot].pid = p.pid;
! 					str = &(saved_chunks[free_slot].data);
  					initStringInfo(str);
  					appendBinaryStringInfo(str,
  										   cursor + PIPE_HEADER_SIZE,
--- 767,791 ----
  
  				for (i = 0; i < CHUNK_SLOTS; i++)
  				{
! 					if (saved_chunks[stripe][i].pid == p.pid)
  					{
  						existing_slot = i;
  						break;
  					}
! 					if (free_slot < 0 && saved_chunks[stripe][i].pid == 0)
  						free_slot = i;
  				}
  				if (existing_slot >= 0)
  				{
! 					str = &(saved_chunks[stripe][existing_slot].data);
  					appendBinaryStringInfo(str,
  										   cursor + PIPE_HEADER_SIZE,
  										   p.len);
  				}
  				else if (free_slot >= 0)
  				{
! 					saved_chunks[stripe][free_slot].pid = p.pid;
! 					str = &(saved_chunks[stripe][free_slot].data);
  					initStringInfo(str);
  					appendBinaryStringInfo(str,
  										   cursor + PIPE_HEADER_SIZE,
***************
*** 803,809 **** process_pipe_input(char *logbuffer, int *bytes_in_logbuffer)
  
  				for (i = 0; i < CHUNK_SLOTS; i++)
  				{
! 					if (saved_chunks[i].pid == p.pid)
  					{
  						existing_slot = i;
  						break;
--- 814,820 ----
  
  				for (i = 0; i < CHUNK_SLOTS; i++)
  				{
! 					if (saved_chunks[stripe][i].pid == p.pid)
  					{
  						existing_slot = i;
  						break;
***************
*** 811,822 **** process_pipe_input(char *logbuffer, int *bytes_in_logbuffer)
  				}
  				if (existing_slot >= 0)
  				{
! 					str = &(saved_chunks[existing_slot].data);
  					appendBinaryStringInfo(str,
  										   cursor + PIPE_HEADER_SIZE,
  										   p.len);
  					write_syslogger_file(str->data, str->len, dest);
! 					saved_chunks[existing_slot].pid = 0;
  					pfree(str->data);
  				}
  				else
--- 822,833 ----
  				}
  				if (existing_slot >= 0)
  				{
! 					str = &(saved_chunks[stripe][existing_slot].data);
  					appendBinaryStringInfo(str,
  										   cursor + PIPE_HEADER_SIZE,
  										   p.len);
  					write_syslogger_file(str->data, str->len, dest);
! 					saved_chunks[stripe][existing_slot].pid = 0;
  					pfree(str->data);
  				}
  				else
***************
*** 871,890 **** process_pipe_input(char *logbuffer, int *bytes_in_logbuffer)
  static void
  flush_pipe_input(char *logbuffer, int *bytes_in_logbuffer)
  {
! 	int			i;
  	StringInfo	str;
  
  	/* Dump any incomplete protocol messages */
! 	for (i = 0; i < CHUNK_SLOTS; i++)
! 	{
! 		if (saved_chunks[i].pid != 0)
  		{
! 			str = &(saved_chunks[i].data);
! 			write_syslogger_file(str->data, str->len, LOG_DESTINATION_STDERR);
! 			saved_chunks[i].pid = 0;
! 			pfree(str->data);
  		}
- 	}
  
  	/*
  	 * Force out any remaining pipe data as-is; we don't bother trying to
--- 882,902 ----
  static void
  flush_pipe_input(char *logbuffer, int *bytes_in_logbuffer)
  {
! 	int			i, stripe;
  	StringInfo	str;
  
  	/* Dump any incomplete protocol messages */
! 	for (stripe = 0; stripe < CHUNK_STRIPES; stripe++)
! 		for (i = 0; i < CHUNK_SLOTS; i++)
  		{
! 			if (saved_chunks[stripe][i].pid != 0)
! 			{
! 				str = &(saved_chunks[stripe][i].data);
! 				write_syslogger_file(str->data, str->len, LOG_DESTINATION_STDERR);
! 				saved_chunks[stripe][i].pid = 0;
! 				pfree(str->data);
! 			}
  		}
  
  	/*
  	 * Force out any remaining pipe data as-is; we don't bother trying to