src/backend/storage/ipc/sinval.c

   1 /*-------------------------------------------------------------------------
   2  *
   3  * sinval.c
   4  *        POSTGRES shared cache invalidation communication code.
   5  *
   6  * Portions Copyright (c) 1996-2024, PostgreSQL Global Development Group
   7  * Portions Copyright (c) 1994, Regents of the University of California
   8  *
   9  *
  10  * IDENTIFICATION
  11  *        src/backend/storage/ipc/sinval.c
  12  *
  13  *-------------------------------------------------------------------------
  14  */
  15 #include "postgres.h"
  16
  17 #include "access/xact.h"
  18 #include "miscadmin.h"
  19 #include "storage/latch.h"
  20 #include "storage/sinvaladt.h"
  21 #include "utils/inval.h"
  22
  23
  24 uint64          SharedInvalidMessageCounter;
  25
  26
  27 /*
  28  * Because backends sitting idle will not be reading sinval events, we
  29  * need a way to give an idle backend a swift kick in the rear and make
  30  * it catch up before the sinval queue overflows and forces it to go
  31  * through a cache reset exercise.  This is done by sending
  32  * PROCSIG_CATCHUP_INTERRUPT to any backend that gets too far behind.
  33  *
  34  * The signal handler will set an interrupt pending flag and will set the
  35  * processes latch. Whenever starting to read from the client, or when
  36  * interrupted while doing so, ProcessClientReadInterrupt() will call
  37  * ProcessCatchupEvent().
  38  */
  39 volatile sig_atomic_t catchupInterruptPending = false;
  40
  41
  42 /*
  43  * SendSharedInvalidMessages
  44  *      Add shared-cache-invalidation message(s) to the global SI message queue.
  45  */
  46 void
  47 SendSharedInvalidMessages(const SharedInvalidationMessage *msgs, int n)
  48 {
  49         SIInsertDataEntries(msgs, n);
  50 }
  51
  52 /*
  53  * ReceiveSharedInvalidMessages
  54  *              Process shared-cache-invalidation messages waiting for this backend
  55  *
  56  * We guarantee to process all messages that had been queued before the
  57  * routine was entered.  It is of course possible for more messages to get
  58  * queued right after our last SIGetDataEntries call.
  59  *
  60  * NOTE: it is entirely possible for this routine to be invoked recursively
  61  * as a consequence of processing inside the invalFunction or resetFunction.
  62  * Furthermore, such a recursive call must guarantee that all outstanding
  63  * inval messages have been processed before it exits.  This is the reason
  64  * for the strange-looking choice to use a statically allocated buffer array
  65  * and counters; it's so that a recursive call can process messages already
  66  * sucked out of sinvaladt.c.
  67  */
  68 void
  69 ReceiveSharedInvalidMessages(void (*invalFunction) (SharedInvalidationMessage *msg),
  70                                                          void (*resetFunction) (void))
  71 {
  72 #define MAXINVALMSGS 32
  73         static SharedInvalidationMessage messages[MAXINVALMSGS];
  74
  75         /*
  76          * We use volatile here to prevent bugs if a compiler doesn't realize that
  77          * recursion is a possibility ...
  78          */
  79         static volatile int nextmsg = 0;
  80         static volatile int nummsgs = 0;
  81
  82         /* Deal with any messages still pending from an outer recursion */
  83         while (nextmsg < nummsgs)
  84         {
  85                 SharedInvalidationMessage msg = messages[nextmsg++];
  86
  87                 SharedInvalidMessageCounter++;
  88                 invalFunction(&msg);
  89         }
  90
  91         do
  92         {
  93                 int                     getResult;
  94
  95                 nextmsg = nummsgs = 0;
  96
  97                 /* Try to get some more messages */
  98                 getResult = SIGetDataEntries(messages, MAXINVALMSGS);
  99
 100                 if (getResult < 0)
 101                 {
 102                         /* got a reset message */
 103                         elog(DEBUG4, "cache state reset");
 104                         SharedInvalidMessageCounter++;
 105                         resetFunction();
 106                         break;                          /* nothing more to do */
 107                 }
 108
 109                 /* Process them, being wary that a recursive call might eat some */
 110                 nextmsg = 0;
 111                 nummsgs = getResult;
 112
 113                 while (nextmsg < nummsgs)
 114                 {
 115                         SharedInvalidationMessage msg = messages[nextmsg++];
 116
 117                         SharedInvalidMessageCounter++;
 118                         invalFunction(&msg);
 119                 }
 120
 121                 /*
 122                  * We only need to loop if the last SIGetDataEntries call (which might
 123                  * have been within a recursive call) returned a full buffer.
 124                  */
 125         } while (nummsgs == MAXINVALMSGS);
 126
 127         /*
 128          * We are now caught up.  If we received a catchup signal, reset that
 129          * flag, and call SICleanupQueue().  This is not so much because we need
 130          * to flush dead messages right now, as that we want to pass on the
 131          * catchup signal to the next slowest backend.  "Daisy chaining" the
 132          * catchup signal this way avoids creating spikes in system load for what
 133          * should be just a background maintenance activity.
 134          */
 135         if (catchupInterruptPending)
 136         {
 137                 catchupInterruptPending = false;
 138                 elog(DEBUG4, "sinval catchup complete, cleaning queue");
 139                 SICleanupQueue(false, 0);
 140         }
 141 }
 142
 143
 144 /*
 145  * HandleCatchupInterrupt
 146  *
 147  * This is called when PROCSIG_CATCHUP_INTERRUPT is received.
 148  *
 149  * We used to directly call ProcessCatchupEvent directly when idle. These days
 150  * we just set a flag to do it later and notify the process of that fact by
 151  * setting the process's latch.
 152  */
 153 void
 154 HandleCatchupInterrupt(void)
 155 {
 156         /*
 157          * Note: this is called by a SIGNAL HANDLER. You must be very wary what
 158          * you do here.
 159          */
 160
 161         catchupInterruptPending = true;
 162
 163         /* make sure the event is processed in due course */
 164         SetLatch(MyLatch);
 165 }
 166
 167 /*
 168  * ProcessCatchupInterrupt
 169  *
 170  * The portion of catchup interrupt handling that runs outside of the signal
 171  * handler, which allows it to actually process pending invalidations.
 172  */
 173 void
 174 ProcessCatchupInterrupt(void)
 175 {
 176         while (catchupInterruptPending)
 177         {
 178                 /*
 179                  * What we need to do here is cause ReceiveSharedInvalidMessages() to
 180                  * run, which will do the necessary work and also reset the
 181                  * catchupInterruptPending flag.  If we are inside a transaction we
 182                  * can just call AcceptInvalidationMessages() to do this.  If we
 183                  * aren't, we start and immediately end a transaction; the call to
 184                  * AcceptInvalidationMessages() happens down inside transaction start.
 185                  *
 186                  * It is awfully tempting to just call AcceptInvalidationMessages()
 187                  * without the rest of the xact start/stop overhead, and I think that
 188                  * would actually work in the normal case; but I am not sure that
 189                  * things would clean up nicely if we got an error partway through.
 190                  */
 191                 if (IsTransactionOrTransactionBlock())
 192                 {
 193                         elog(DEBUG4, "ProcessCatchupEvent inside transaction");
 194                         AcceptInvalidationMessages();
 195                 }
 196                 else
 197                 {
 198                         elog(DEBUG4, "ProcessCatchupEvent outside transaction");
 199                         StartTransactionCommand();
 200                         CommitTransactionCommand();
 201                 }
 202         }
 203 }