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buf_init.c
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1 /*-------------------------------------------------------------------------
2  *
3  * buf_init.c
4  * buffer manager initialization routines
5  *
6  * Portions Copyright (c) 1996-2021, PostgreSQL Global Development Group
7  * Portions Copyright (c) 1994, Regents of the University of California
8  *
9  *
10  * IDENTIFICATION
11  * src/backend/storage/buffer/buf_init.c
12  *
13  *-------------------------------------------------------------------------
14  */
15 #include "postgres.h"
16 
17 #include "storage/buf_internals.h"
18 #include "storage/bufmgr.h"
19 
25 
26 
27 /*
28  * Data Structures:
29  * buffers live in a freelist and a lookup data structure.
30  *
31  *
32  * Buffer Lookup:
33  * Two important notes. First, the buffer has to be
34  * available for lookup BEFORE an IO begins. Otherwise
35  * a second process trying to read the buffer will
36  * allocate its own copy and the buffer pool will
37  * become inconsistent.
38  *
39  * Buffer Replacement:
40  * see freelist.c. A buffer cannot be replaced while in
41  * use either by data manager or during IO.
42  *
43  *
44  * Synchronization/Locking:
45  *
46  * IO_IN_PROGRESS -- this is a flag in the buffer descriptor.
47  * It must be set when an IO is initiated and cleared at
48  * the end of the IO. It is there to make sure that one
49  * process doesn't start to use a buffer while another is
50  * faulting it in. see WaitIO and related routines.
51  *
52  * refcount -- Counts the number of processes holding pins on a buffer.
53  * A buffer is pinned during IO and immediately after a BufferAlloc().
54  * Pins must be released before end of transaction. For efficiency the
55  * shared refcount isn't increased if an individual backend pins a buffer
56  * multiple times. Check the PrivateRefCount infrastructure in bufmgr.c.
57  */
58 
59 
60 /*
61  * Initialize shared buffer pool
62  *
63  * This is called once during shared-memory initialization (either in the
64  * postmaster, or in a standalone backend).
65  */
66 void
68 {
69  bool foundBufs,
70  foundDescs,
71  foundIOCV,
72  foundBufCkpt;
73 
74  /* Align descriptors to a cacheline boundary. */
75  BufferDescriptors = (BufferDescPadded *)
76  ShmemInitStruct("Buffer Descriptors",
77  NBuffers * sizeof(BufferDescPadded),
78  &foundDescs);
79 
80  BufferBlocks = (char *)
81  ShmemInitStruct("Buffer Blocks",
82  NBuffers * (Size) BLCKSZ, &foundBufs);
83 
84  /* Align condition variables to cacheline boundary. */
85  BufferIOCVArray = (ConditionVariableMinimallyPadded *)
86  ShmemInitStruct("Buffer IO Condition Variables",
88  &foundIOCV);
89 
90  /*
91  * The array used to sort to-be-checkpointed buffer ids is located in
92  * shared memory, to avoid having to allocate significant amounts of
93  * memory at runtime. As that'd be in the middle of a checkpoint, or when
94  * the checkpointer is restarted, memory allocation failures would be
95  * painful.
96  */
97  CkptBufferIds = (CkptSortItem *)
98  ShmemInitStruct("Checkpoint BufferIds",
99  NBuffers * sizeof(CkptSortItem), &foundBufCkpt);
100 
101  if (foundDescs || foundBufs || foundIOCV || foundBufCkpt)
102  {
103  /* should find all of these, or none of them */
104  Assert(foundDescs && foundBufs && foundIOCV && foundBufCkpt);
105  /* note: this path is only taken in EXEC_BACKEND case */
106  }
107  else
108  {
109  int i;
110 
111  /*
112  * Initialize all the buffer headers.
113  */
114  for (i = 0; i < NBuffers; i++)
115  {
117 
118  CLEAR_BUFFERTAG(buf->tag);
119 
120  pg_atomic_init_u32(&buf->state, 0);
121  buf->wait_backend_pid = 0;
122 
123  buf->buf_id = i;
124 
125  /*
126  * Initially link all the buffers together as unused. Subsequent
127  * management of this list is done by freelist.c.
128  */
129  buf->freeNext = i + 1;
130 
133 
135  }
136 
137  /* Correct last entry of linked list */
138  GetBufferDescriptor(NBuffers - 1)->freeNext = FREENEXT_END_OF_LIST;
139  }
140 
141  /* Init other shared buffer-management stuff */
142  StrategyInitialize(!foundDescs);
143 
144  /* Initialize per-backend file flush context */
145  WritebackContextInit(&BackendWritebackContext,
147 }
148 
149 /*
150  * BufferShmemSize
151  *
152  * compute the size of shared memory for the buffer pool including
153  * data pages, buffer descriptors, hash tables, etc.
154  */
155 Size
157 {
158  Size size = 0;
159 
160  /* size of buffer descriptors */
161  size = add_size(size, mul_size(NBuffers, sizeof(BufferDescPadded)));
162  /* to allow aligning buffer descriptors */
163  size = add_size(size, PG_CACHE_LINE_SIZE);
164 
165  /* size of data pages */
166  size = add_size(size, mul_size(NBuffers, BLCKSZ));
167 
168  /* size of stuff controlled by freelist.c */
169  size = add_size(size, StrategyShmemSize());
170 
171  /* size of I/O condition variables */
172  size = add_size(size, mul_size(NBuffers,
174  /* to allow aligning the above */
175  size = add_size(size, PG_CACHE_LINE_SIZE);
176 
177  /* size of checkpoint sort array in bufmgr.c */
178  size = add_size(size, mul_size(NBuffers, sizeof(CkptSortItem)));
179 
180  return size;
181 }
#define PG_CACHE_LINE_SIZE
#define FREENEXT_END_OF_LIST
int wait_backend_pid
int backend_flush_after
Definition: bufmgr.c:158
void StrategyInitialize(bool init)
Definition: freelist.c:475
void WritebackContextInit(WritebackContext *context, int *max_pending)
Definition: bufmgr.c:4722
void ConditionVariableInit(ConditionVariable *cv)
void * ShmemInitStruct(const char *name, Size size, bool *foundPtr)
Definition: shmem.c:396
WritebackContext BackendWritebackContext
Definition: buf_init.c:23
static char * buf
Definition: pg_test_fsync.c:68
BufferDescPadded * BufferDescriptors
Definition: buf_init.c:20
#define GetBufferDescriptor(id)
#define BufferDescriptorGetIOCV(bdesc)
void InitBufferPool(void)
Definition: buf_init.c:67
void LWLockInitialize(LWLock *lock, int tranche_id)
Definition: lwlock.c:736
Size mul_size(Size s1, Size s2)
Definition: shmem.c:519
Size add_size(Size s1, Size s2)
Definition: shmem.c:502
ConditionVariableMinimallyPadded * BufferIOCVArray
Definition: buf_init.c:22
#define BufferDescriptorGetContentLock(bdesc)
#define Assert(condition)
Definition: c.h:804
#define CLEAR_BUFFERTAG(a)
Definition: buf_internals.h:98
CkptSortItem * CkptBufferIds
Definition: buf_init.c:24
size_t Size
Definition: c.h:540
BufferTag tag
Size BufferShmemSize(void)
Definition: buf_init.c:156
int i
int NBuffers
Definition: globals.c:135
pg_atomic_uint32 state
static void pg_atomic_init_u32(volatile pg_atomic_uint32 *ptr, uint32 val)
Definition: atomics.h:223
char * BufferBlocks
Definition: buf_init.c:21
Size StrategyShmemSize(void)
Definition: freelist.c:454