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/*-------------------------------------------------------------------------
*
* walprotocol.h
* Definitions relevant to the streaming WAL transmission protocol.
*
* Portions Copyright (c) 2010-2010, PostgreSQL Global Development Group
*
* src/include/replication/walprotocol.h
*
*-------------------------------------------------------------------------
*/
#ifndef _WALPROTOCOL_H
#define _WALPROTOCOL_H
#include "access/xlogdefs.h"
#include "utils/timestamp.h"
/*
* Header for a WAL data message (message type 'w'). This is wrapped within
* a CopyData message at the FE/BE protocol level.
*
* The header is followed by actual WAL data. Note that the data length is
* not specified in the header --- it's just whatever remains in the message.
*
* walEnd and sendTime are not essential data, but are provided in case
* the receiver wants to adjust its behavior depending on how far behind
* it is.
*/
typedef struct
{
/* WAL start location of the data included in this message */
XLogRecPtr dataStart;
/* Current end of WAL on the sender */
XLogRecPtr walEnd;
/* Sender's system clock at the time of transmission */
TimestampTz sendTime;
} WalDataMessageHeader;
/*
* Maximum data payload in a WAL data message. Must be >= XLOG_BLCKSZ.
*
* We don't have a good idea of what a good value would be; there's some
* overhead per message in both walsender and walreceiver, but on the other
* hand sending large batches makes walsender less responsive to signals
* because signals are checked only between messages. 128kB (with
* default 8k blocks) seems like a reasonable guess for now.
*/
#define MAX_SEND_SIZE (XLOG_BLCKSZ * 16)
#endif /* _WALPROTOCOL_H */
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