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Diffstat (limited to 'src/backend/replication/walsender.c')
| -rw-r--r-- | src/backend/replication/walsender.c | 851 |
1 files changed, 851 insertions, 0 deletions
diff --git a/src/backend/replication/walsender.c b/src/backend/replication/walsender.c new file mode 100644 index 00000000000..8a3352e0755 --- /dev/null +++ b/src/backend/replication/walsender.c @@ -0,0 +1,851 @@ +/*------------------------------------------------------------------------- + * + * walsender.c + * + * The WAL sender process (walsender) is new as of Postgres 8.5. It takes + * charge of XLOG streaming sender in the primary server. At first, it is + * started by the postmaster when the walreceiver in the standby server + * connects to the primary server and requests XLOG streaming replication, + * i.e., unlike any auxiliary process, it is not an always-running process. + * It attempts to keep reading XLOG records from the disk and sending them + * to the standby server, as long as the connection is alive (i.e., like + * any backend, there is an one to one relationship between a connection + * and a walsender process). + * + * Normal termination is by SIGTERM, which instructs the walsender to + * close the connection and exit(0) at next convenient moment. Emergency + * termination is by SIGQUIT; like any backend, the walsender will simply + * abort and exit on SIGQUIT. A close of the connection and a FATAL error + * are treated as not a crash but approximately normal termination; + * the walsender will exit quickly without sending any more XLOG records. + * + * If the server is shut down, postmaster sends us SIGUSR2 after all + * regular backends have exited and the shutdown checkpoint has been written. + * This instruct walsender to send any outstanding WAL, including the + * shutdown checkpoint record, and then exit. + * + * Note that there can be more than one walsender process concurrently. + * + * Portions Copyright (c) 2010-2010, PostgreSQL Global Development Group + * + * + * IDENTIFICATION + * $PostgreSQL: pgsql/src/backend/replication/walsender.c,v 1.1 2010/01/15 09:19:03 heikki Exp $ + * + *------------------------------------------------------------------------- + */ +#include "postgres.h" + +#include <unistd.h> + +#include "access/xlog_internal.h" +#include "catalog/pg_type.h" +#include "libpq/libpq.h" +#include "libpq/pqformat.h" +#include "libpq/pqsignal.h" +#include "miscadmin.h" +#include "replication/walsender.h" +#include "storage/fd.h" +#include "storage/ipc.h" +#include "storage/lock.h" +#include "storage/pmsignal.h" +#include "tcop/tcopprot.h" +#include "utils/guc.h" +#include "utils/memutils.h" +#include "utils/ps_status.h" + +/* Array of WalSnds in shared memory */ +WalSndCtlData *WalSndCtl = NULL; + +/* My slot in the shared memory array */ +static WalSnd *MyWalSnd = NULL; + +/* Global state */ +bool am_walsender = false; /* Am I a walsender process ? */ + +/* User-settable parameters for walsender */ +int MaxWalSenders = 0; /* the maximum number of concurrent walsenders */ +int WalSndDelay = 200; /* max sleep time between some actions */ + +#define NAPTIME_PER_CYCLE 100 /* max sleep time between cycles (100ms) */ + +/* + * These variables are used similarly to openLogFile/Id/Seg/Off, + * but for walsender to read the XLOG. + */ +static int sendFile = -1; +static uint32 sendId = 0; +static uint32 sendSeg = 0; +static uint32 sendOff = 0; + +/* + * How far have we sent WAL already? This is also advertised in + * MyWalSnd->sentPtr. + */ +static XLogRecPtr sentPtr = {0, 0}; + +/* Flags set by signal handlers for later service in main loop */ +static volatile sig_atomic_t got_SIGHUP = false; +static volatile sig_atomic_t shutdown_requested = false; +static volatile sig_atomic_t ready_to_stop = false; + +/* Signal handlers */ +static void WalSndSigHupHandler(SIGNAL_ARGS); +static void WalSndShutdownHandler(SIGNAL_ARGS); +static void WalSndQuickDieHandler(SIGNAL_ARGS); + +/* Prototypes for private functions */ +static int WalSndLoop(void); +static void InitWalSnd(void); +static void WalSndHandshake(void); +static void WalSndKill(int code, Datum arg); +static void XLogRead(char *buf, XLogRecPtr recptr, Size nbytes); +static bool XLogSend(StringInfo outMsg); +static void CheckClosedConnection(void); + +/* + * How much WAL to send in one message? Must be >= XLOG_BLCKSZ. + */ +#define MAX_SEND_SIZE (XLOG_SEG_SIZE / 2) + +/* Main entry point for walsender process */ +int +WalSenderMain(void) +{ + MemoryContext walsnd_context; + + if (!superuser()) + ereport(FATAL, + (errcode(ERRCODE_INSUFFICIENT_PRIVILEGE), + errmsg("must be superuser to start walsender"))); + + /* Create a per-walsender data structure in shared memory */ + InitWalSnd(); + + /* + * Create a memory context that we will do all our work in. We do this so + * that we can reset the context during error recovery and thereby avoid + * possible memory leaks. Formerly this code just ran in + * TopMemoryContext, but resetting that would be a really bad idea. + * + * XXX: we don't actually attempt error recovery in walsender, we just + * close the connection and exit. + */ + walsnd_context = AllocSetContextCreate(TopMemoryContext, + "Wal Sender", + ALLOCSET_DEFAULT_MINSIZE, + ALLOCSET_DEFAULT_INITSIZE, + ALLOCSET_DEFAULT_MAXSIZE); + MemoryContextSwitchTo(walsnd_context); + + /* Unblock signals (they were blocked when the postmaster forked us) */ + PG_SETMASK(&UnBlockSig); + + /* Tell the standby that walsender is ready for receiving commands */ + ReadyForQuery(DestRemote); + + /* Handle handshake messages before streaming */ + WalSndHandshake(); + + /* Main loop of walsender */ + return WalSndLoop(); +} + +static void +WalSndHandshake(void) +{ + StringInfoData input_message; + bool replication_started = false; + + initStringInfo(&input_message); + + while (!replication_started) + { + int firstchar; + + /* Wait for a command to arrive */ + firstchar = pq_getbyte(); + + /* + * Check for any other interesting events that happened while we + * slept. + */ + if (got_SIGHUP) + { + got_SIGHUP = false; + ProcessConfigFile(PGC_SIGHUP); + } + + if (firstchar == EOF) + { + /* standby disconnected */ + ereport(COMMERROR, + (errcode(ERRCODE_PROTOCOL_VIOLATION), + errmsg("unexpected EOF on standby connection"))); + } + else + { + /* + * Read the message contents. This is expected to be done without + * blocking because we've been able to get message type code. + */ + if (pq_getmessage(&input_message, 0)) + firstchar = EOF; /* suitable message already logged */ + } + + + /* Handle the very limited subset of commands expected in this phase */ + + switch (firstchar) + { + case 'Q': /* Query message */ + { + const char *query_string; + XLogRecPtr recptr; + + query_string = pq_getmsgstring(&input_message); + pq_getmsgend(&input_message); + + if (strcmp(query_string, "IDENTIFY_SYSTEM") == 0) + { + StringInfoData buf; + char sysid[32]; + char tli[11]; + + /* + * Reply with a result set with one row, two columns. + * First col is system ID, and second if timeline ID + */ + + snprintf(sysid, sizeof(sysid), UINT64_FORMAT, + GetSystemIdentifier()); + snprintf(tli, sizeof(tli), "%u", ThisTimeLineID); + + /* Send a RowDescription message */ + pq_beginmessage(&buf, 'T'); + pq_sendint(&buf, 2, 2); /* 2 fields */ + + /* first field */ + pq_sendstring(&buf, "systemid"); /* col name */ + pq_sendint(&buf, 0, 4); /* table oid */ + pq_sendint(&buf, 0, 2); /* attnum */ + pq_sendint(&buf, TEXTOID, 4); /* type oid */ + pq_sendint(&buf, -1, 2); /* typlen */ + pq_sendint(&buf, 0, 4); /* typmod */ + pq_sendint(&buf, 0, 2); /* format code */ + + /* second field */ + pq_sendstring(&buf, "timeline"); /* col name */ + pq_sendint(&buf, 0, 4); /* table oid */ + pq_sendint(&buf, 0, 2); /* attnum */ + pq_sendint(&buf, INT4OID, 4); /* type oid */ + pq_sendint(&buf, 4, 2); /* typlen */ + pq_sendint(&buf, 0, 4); /* typmod */ + pq_sendint(&buf, 0, 2); /* format code */ + pq_endmessage(&buf); + + /* Send a DataRow message */ + pq_beginmessage(&buf, 'D'); + pq_sendint(&buf, 2, 2); /* # of columns */ + pq_sendint(&buf, strlen(sysid), 4); /* col1 len */ + pq_sendbytes(&buf, (char *) &sysid, strlen(sysid)); + pq_sendint(&buf, strlen(tli), 4); /* col2 len */ + pq_sendbytes(&buf, (char *) tli, strlen(tli)); + pq_endmessage(&buf); + + /* Send CommandComplete and ReadyForQuery messages */ + EndCommand("SELECT", DestRemote); + ReadyForQuery(DestRemote); + } + else if (sscanf(query_string, "START_REPLICATION %X/%X", + &recptr.xlogid, &recptr.xrecoff) == 2) + { + StringInfoData buf; + + /* Send a CopyOutResponse message, and start streaming */ + pq_beginmessage(&buf, 'H'); + pq_sendbyte(&buf, 0); + pq_sendint(&buf, 0, 2); + pq_endmessage(&buf); + + /* + * Initialize position to the received one, then + * the xlog records begin to be shipped from that position + */ + sentPtr = recptr; + + /* break out of the loop */ + replication_started = true; + } + else + { + ereport(FATAL, + (errcode(ERRCODE_PROTOCOL_VIOLATION), + errmsg("invalid standby query string: %s", query_string))); + } + break; + } + + /* 'X' means that the standby is closing the connection */ + case 'X': + proc_exit(0); + + case EOF: + ereport(ERROR, + (errcode(ERRCODE_PROTOCOL_VIOLATION), + errmsg("unexpected EOF on standby connection"))); + + default: + ereport(FATAL, + (errcode(ERRCODE_PROTOCOL_VIOLATION), + errmsg("invalid standby handshake message type %d", firstchar))); + } + } +} + +/* + * Check if the remote end has closed the connection. + */ +static void +CheckClosedConnection(void) +{ + unsigned char firstchar; + int r; + + r = pq_getbyte_if_available(&firstchar); + if (r < 0) + { + /* no data available */ + if (errno == EAGAIN || errno == EWOULDBLOCK) + return; + + /* + * Ok if interrupted, though it shouldn't really happen with + * a non-blocking operation. + */ + if (errno == EINTR) + return; + + ereport(COMMERROR, + (errcode_for_socket_access(), + errmsg("could not receive data from client: %m"))); + } + if (r == 0) + { + /* standby disconnected unexpectedly */ + ereport(ERROR, + (errcode(ERRCODE_PROTOCOL_VIOLATION), + errmsg("unexpected EOF on standby connection"))); + } + + /* Handle the very limited subset of commands expected in this phase */ + switch (firstchar) + { + /* + * 'X' means that the standby is closing down the socket. EOF means + * unexpected loss of standby connection. Either way, perform normal + * shutdown. + */ + case 'X': + proc_exit(0); + + default: + ereport(FATAL, + (errcode(ERRCODE_PROTOCOL_VIOLATION), + errmsg("invalid standby closing message type %d", + firstchar))); + } +} + +/* Main loop of walsender process */ +static int +WalSndLoop(void) +{ + StringInfoData output_message; + + initStringInfo(&output_message); + + /* Loop forever */ + for (;;) + { + int remain; /* remaining time (ms) */ + + /* + * Emergency bailout if postmaster has died. This is to avoid the + * necessity for manual cleanup of all postmaster children. + */ + if (!PostmasterIsAlive(true)) + exit(1); + /* Process any requests or signals received recently */ + if (got_SIGHUP) + { + got_SIGHUP = false; + ProcessConfigFile(PGC_SIGHUP); + } + + /* + * When SIGUSR2 arrives, we send all outstanding logs up to the + * shutdown checkpoint record (i.e., the latest record) and exit. + */ + if (ready_to_stop) + { + XLogSend(&output_message); + shutdown_requested = true; + } + + /* Normal exit from the walsender is here */ + if (shutdown_requested) + { + /* Inform the standby that XLOG streaming was done */ + pq_puttextmessage('C', "COPY 0"); + pq_flush(); + + proc_exit(0); + } + + /* + * Nap for the configured time or until a message arrives. + * + * On some platforms, signals won't interrupt the sleep. To ensure we + * respond reasonably promptly when someone signals us, break down the + * sleep into NAPTIME_PER_CYCLE (ms) increments, and check for + * interrupts after each nap. + */ + remain = WalSndDelay; + while (remain > 0) + { + if (got_SIGHUP || shutdown_requested || ready_to_stop) + break; + + /* + * Check to see whether a message from the standby or an interrupt + * from other processes has arrived. + */ + pg_usleep(remain > NAPTIME_PER_CYCLE ? NAPTIME_PER_CYCLE : remain); + CheckClosedConnection(); + + remain -= NAPTIME_PER_CYCLE; + } + + /* Attempt to send the log once every loop */ + if (!XLogSend(&output_message)) + goto eof; + } + + /* can't get here because the above loop never exits */ + return 1; + +eof: + /* + * Reset whereToSendOutput to prevent ereport from attempting + * to send any more messages to the standby. + */ + if (whereToSendOutput == DestRemote) + whereToSendOutput = DestNone; + + proc_exit(0); + return 1; /* keep the compiler quiet */ +} + +/* Initialize a per-walsender data structure for this walsender process */ +static void +InitWalSnd(void) +{ + /* use volatile pointer to prevent code rearrangement */ + volatile WalSndCtlData *walsndctl = WalSndCtl; + int i; + + /* + * WalSndCtl should be set up already (we inherit this by fork() or + * EXEC_BACKEND mechanism from the postmaster). + */ + Assert(walsndctl != NULL); + Assert(MyWalSnd == NULL); + + /* + * Find a free walsender slot and reserve it. If this fails, we must be + * out of WalSnd structures. + */ + for (i = 0; i < MaxWalSenders; i++) + { + volatile WalSnd *walsnd = &WalSndCtl->walsnds[i]; + + SpinLockAcquire(&walsnd->mutex); + + if (walsnd->pid != 0) + { + SpinLockRelease(&walsnd->mutex); + continue; + } + else + { + /* found */ + MyWalSnd = (WalSnd *) walsnd; + walsnd->pid = MyProcPid; + MemSet(&MyWalSnd->sentPtr, 0, sizeof(XLogRecPtr)); + SpinLockRelease(&walsnd->mutex); + break; + } + } + if (MyWalSnd == NULL) + ereport(FATAL, + (errcode(ERRCODE_TOO_MANY_CONNECTIONS), + errmsg("sorry, too many standbys already"))); + + /* Arrange to clean up at walsender exit */ + on_shmem_exit(WalSndKill, 0); +} + +/* Destroy the per-walsender data structure for this walsender process */ +static void +WalSndKill(int code, Datum arg) +{ + Assert(MyWalSnd != NULL); + + /* + * Mark WalSnd struct no longer in use. Assume that no lock is required + * for this. + */ + MyWalSnd->pid = 0; + + /* WalSnd struct isn't mine anymore */ + MyWalSnd = NULL; +} + +/* + * Read 'nbytes' bytes from WAL into 'buf', starting at location 'recptr' + */ +void +XLogRead(char *buf, XLogRecPtr recptr, Size nbytes) +{ + char path[MAXPGPATH]; + uint32 startoff; + + while (nbytes > 0) + { + int segbytes; + int readbytes; + + startoff = recptr.xrecoff % XLogSegSize; + + if (sendFile < 0 || !XLByteInSeg(recptr, sendId, sendSeg)) + { + /* Switch to another logfile segment */ + if (sendFile >= 0) + close(sendFile); + + XLByteToSeg(recptr, sendId, sendSeg); + XLogFilePath(path, ThisTimeLineID, sendId, sendSeg); + + sendFile = BasicOpenFile(path, O_RDONLY | PG_BINARY, 0); + if (sendFile < 0) + ereport(FATAL, /* XXX: Why FATAL? */ + (errcode_for_file_access(), + errmsg("could not open file \"%s\" (log file %u, segment %u): %m", + path, sendId, sendSeg))); + sendOff = 0; + } + + /* Need to seek in the file? */ + if (sendOff != startoff) + { + if (lseek(sendFile, (off_t) startoff, SEEK_SET) < 0) + ereport(FATAL, + (errcode_for_file_access(), + errmsg("could not seek in log file %u, segment %u to offset %u: %m", + sendId, sendSeg, startoff))); + sendOff = startoff; + } + + /* How many bytes are within this segment? */ + if (nbytes > (XLogSegSize - startoff)) + segbytes = XLogSegSize - startoff; + else + segbytes = nbytes; + + readbytes = read(sendFile, buf, segbytes); + if (readbytes <= 0) + ereport(FATAL, + (errcode_for_file_access(), + errmsg("could not read from log file %u, segment %u, offset %u, " + "length %lu: %m", + sendId, sendSeg, sendOff, (unsigned long) segbytes))); + + /* Update state for read */ + XLByteAdvance(recptr, readbytes); + + sendOff += readbytes; + nbytes -= readbytes; + buf += readbytes; + } +} + +/* + * Read all WAL that's been written (and flushed) since last cycle, and send + * it to client. + * + * Returns true if OK, false if trouble. + */ +static bool +XLogSend(StringInfo outMsg) +{ + XLogRecPtr SendRqstPtr; + char activitymsg[50]; + /* use volatile pointer to prevent code rearrangement */ + volatile WalSnd *walsnd = MyWalSnd; + + /* + * Invalid position means that we have not yet received the initial + * CopyData message from the slave that indicates where to start the + * streaming. + */ + if (sentPtr.xlogid == 0 && + sentPtr.xrecoff == 0) + return true; + + /* Attempt to send all the records which were written to the disk */ + SendRqstPtr = GetWriteRecPtr(); + + /* Quick exit if nothing to do */ + if (!XLByteLT(sentPtr, SendRqstPtr)) + return true; + + /* + * Since successive pages in a segment are consecutively written, + * we can gather multiple records together by issuing just one + * read() call, and send them as one CopyData message at one time; + * nmsgs is the number of CopyData messages sent in this XLogSend; + * npages is the number of pages we have determined can be read and + * sent together; startpos is the starting position of reading and + * sending in the first page, startoff is the file offset at which + * it should go and endpos is the end position of reading and + * sending in the last page. We must initialize all of them to + * keep the compiler quiet. + */ + + while (XLByteLT(sentPtr, SendRqstPtr)) + { + XLogRecPtr startptr; + XLogRecPtr endptr; + Size nbytes; + + /* + * Figure out how much to send in one message. If there's less than + * MAX_SEND_SIZE bytes to send, send everything. Otherwise send + * MAX_SEND_SIZE bytes, but round to page boundary for efficiency. + */ + startptr = sentPtr; + endptr = startptr; + XLByteAdvance(endptr, MAX_SEND_SIZE); + + /* + * Round down to page boundary. This is not only for performance + * reasons, walreceiver relies on the fact that we never split a WAL + * record across two messages. Since a long WAL record is split at + * page boundary into continuation records, page boundary is always + * safe cut-off point. We also assume that SendRqstPtr never points + * in the middle of a WAL record. + */ + endptr.xrecoff -= (endptr.xrecoff % XLOG_BLCKSZ); + + if (XLByteLT(SendRqstPtr, endptr)) + endptr = SendRqstPtr; + + /* + * OK to read and send the log. + * + * We don't need to convert the xlogid/xrecoff from host byte order + * to network byte order because the both server can be expected to + * have the same byte order. If they have the different order, we + * don't reach here. + */ + pq_sendbytes(outMsg, (char *) &startptr, sizeof(startptr)); + + if (endptr.xlogid != startptr.xlogid) + { + Assert(endptr.xlogid == startptr.xlogid + 1); + nbytes = endptr.xrecoff + XLogFileSize - startptr.xrecoff; + } + else + nbytes = endptr.xrecoff - startptr.xrecoff; + + sentPtr = endptr; + + /* + * Read the log into the output buffer directly to prevent + * extra memcpy calls. + */ + enlargeStringInfo(outMsg, nbytes); + + XLogRead(&outMsg->data[outMsg->len], startptr, nbytes); + outMsg->len += nbytes; + outMsg->data[outMsg->len] = '\0'; + + pq_putmessage('d', outMsg->data, outMsg->len); + resetStringInfo(outMsg); + } + + /* Update shared memory status */ + SpinLockAcquire(&walsnd->mutex); + walsnd->sentPtr = sentPtr; + SpinLockRelease(&walsnd->mutex); + + /* Flush pending output */ + if (pq_flush()) + return false; + + /* Report progress of XLOG streaming in PS display */ + snprintf(activitymsg, sizeof(activitymsg), "streaming %X/%X", + sentPtr.xlogid, sentPtr.xrecoff); + set_ps_display(activitymsg, false); + + return true; +} + +/* SIGHUP: set flag to re-read config file at next convenient time */ +static void +WalSndSigHupHandler(SIGNAL_ARGS) +{ + got_SIGHUP = true; +} + +/* SIGTERM: set flag to shut down */ +static void +WalSndShutdownHandler(SIGNAL_ARGS) +{ + shutdown_requested = true; +} + +/* + * WalSndQuickDieHandler() occurs when signalled SIGQUIT by the postmaster. + * + * Some backend has bought the farm, + * so we need to stop what we're doing and exit. + */ +static void +WalSndQuickDieHandler(SIGNAL_ARGS) +{ + PG_SETMASK(&BlockSig); + + /* + * We DO NOT want to run proc_exit() callbacks -- we're here because + * shared memory may be corrupted, so we don't want to try to clean up our + * transaction. Just nail the windows shut and get out of town. Now that + * there's an atexit callback to prevent third-party code from breaking + * things by calling exit() directly, we have to reset the callbacks + * explicitly to make this work as intended. + */ + on_exit_reset(); + + /* + * Note we do exit(2) not exit(0). This is to force the postmaster into a + * system reset cycle if some idiot DBA sends a manual SIGQUIT to a random + * backend. This is necessary precisely because we don't clean up our + * shared memory state. (The "dead man switch" mechanism in pmsignal.c + * should ensure the postmaster sees this as a crash, too, but no harm + * in being doubly sure.) + */ + exit(2); +} + +/* SIGUSR2: set flag to do a last cycle and shut down afterwards */ +static void +WalSndLastCycleHandler(SIGNAL_ARGS) +{ + ready_to_stop = true; +} + +/* Set up signal handlers */ +void +WalSndSignals(void) +{ + /* Set up signal handlers */ + pqsignal(SIGHUP, WalSndSigHupHandler); /* set flag to read config file */ + pqsignal(SIGINT, SIG_IGN); /* not used */ + pqsignal(SIGTERM, WalSndShutdownHandler); /* request shutdown */ + pqsignal(SIGQUIT, WalSndQuickDieHandler); /* hard crash time */ + pqsignal(SIGALRM, SIG_IGN); + pqsignal(SIGPIPE, SIG_IGN); + pqsignal(SIGUSR1, SIG_IGN); /* not used */ + pqsignal(SIGUSR2, WalSndLastCycleHandler); /* request a last cycle and shutdown */ + + /* Reset some signals that are accepted by postmaster but not here */ + pqsignal(SIGCHLD, SIG_DFL); + pqsignal(SIGTTIN, SIG_DFL); + pqsignal(SIGTTOU, SIG_DFL); + pqsignal(SIGCONT, SIG_DFL); + pqsignal(SIGWINCH, SIG_DFL); +} + +/* Report shared-memory space needed by WalSndShmemInit */ +Size +WalSndShmemSize(void) +{ + Size size = 0; + + size = offsetof(WalSndCtlData, walsnds); + size = add_size(size, mul_size(MaxWalSenders, sizeof(WalSnd))); + + return size; +} + +/* Allocate and initialize walsender-related shared memory */ +void +WalSndShmemInit(void) +{ + bool found; + int i; + + WalSndCtl = (WalSndCtlData *) + ShmemInitStruct("Wal Sender Ctl", WalSndShmemSize(), &found); + + if (WalSndCtl == NULL) + ereport(FATAL, + (errcode(ERRCODE_OUT_OF_MEMORY), + errmsg("not enough shared memory for walsender"))); + if (found) + return; /* already initialized */ + + /* Initialize the data structures */ + MemSet(WalSndCtl, 0, WalSndShmemSize()); + + for (i = 0; i < MaxWalSenders; i++) + { + WalSnd *walsnd = &WalSndCtl->walsnds[i]; + SpinLockInit(&walsnd->mutex); + } +} + +/* + * Returns the oldest Send position among walsenders. Or InvalidXLogRecPtr + * if none. + */ +XLogRecPtr +GetOldestWALSendPointer(void) +{ + XLogRecPtr oldest = {0, 0}; + int i; + bool found = false; + + for (i = 0; i < MaxWalSenders; i++) + { + /* use volatile pointer to prevent code rearrangement */ + volatile WalSnd *walsnd = &WalSndCtl->walsnds[i]; + XLogRecPtr recptr; + + if (walsnd->pid == 0) + continue; + + SpinLockAcquire(&walsnd->mutex); + recptr = walsnd->sentPtr; + SpinLockRelease(&walsnd->mutex); + + if (recptr.xlogid == 0 && recptr.xrecoff == 0) + continue; + + if (!found || XLByteLT(recptr, oldest)) + oldest = recptr; + found = true; + } + return oldest; +} |