PostgreSQL Source Code  git master
buf_init.c
Go to the documentation of this file.
1 /*-------------------------------------------------------------------------
2  *
3  * buf_init.c
4  * buffer manager initialization routines
5  *
6  * Portions Copyright (c) 1996-2022, 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 #include "storage/proc.h"
20 
26 
27 
28 /*
29  * Data Structures:
30  * buffers live in a freelist and a lookup data structure.
31  *
32  *
33  * Buffer Lookup:
34  * Two important notes. First, the buffer has to be
35  * available for lookup BEFORE an IO begins. Otherwise
36  * a second process trying to read the buffer will
37  * allocate its own copy and the buffer pool will
38  * become inconsistent.
39  *
40  * Buffer Replacement:
41  * see freelist.c. A buffer cannot be replaced while in
42  * use either by data manager or during IO.
43  *
44  *
45  * Synchronization/Locking:
46  *
47  * IO_IN_PROGRESS -- this is a flag in the buffer descriptor.
48  * It must be set when an IO is initiated and cleared at
49  * the end of the IO. It is there to make sure that one
50  * process doesn't start to use a buffer while another is
51  * faulting it in. see WaitIO and related routines.
52  *
53  * refcount -- Counts the number of processes holding pins on a buffer.
54  * A buffer is pinned during IO and immediately after a BufferAlloc().
55  * Pins must be released before end of transaction. For efficiency the
56  * shared refcount isn't increased if an individual backend pins a buffer
57  * multiple times. Check the PrivateRefCount infrastructure in bufmgr.c.
58  */
59 
60 
61 /*
62  * Initialize shared buffer pool
63  *
64  * This is called once during shared-memory initialization (either in the
65  * postmaster, or in a standalone backend).
66  */
67 void
69 {
70  bool foundBufs,
71  foundDescs,
72  foundIOCV,
73  foundBufCkpt;
74 
75  /* Align descriptors to a cacheline boundary. */
77  ShmemInitStruct("Buffer Descriptors",
78  NBuffers * sizeof(BufferDescPadded),
79  &foundDescs);
80 
81  BufferBlocks = (char *)
82  ShmemInitStruct("Buffer Blocks",
83  NBuffers * (Size) BLCKSZ, &foundBufs);
84 
85  /* Align condition variables to cacheline boundary. */
87  ShmemInitStruct("Buffer IO Condition Variables",
89  &foundIOCV);
90 
91  /*
92  * The array used to sort to-be-checkpointed buffer ids is located in
93  * shared memory, to avoid having to allocate significant amounts of
94  * memory at runtime. As that'd be in the middle of a checkpoint, or when
95  * the checkpointer is restarted, memory allocation failures would be
96  * painful.
97  */
99  ShmemInitStruct("Checkpoint BufferIds",
100  NBuffers * sizeof(CkptSortItem), &foundBufCkpt);
101 
102  if (foundDescs || foundBufs || foundIOCV || foundBufCkpt)
103  {
104  /* should find all of these, or none of them */
105  Assert(foundDescs && foundBufs && foundIOCV && foundBufCkpt);
106  /* note: this path is only taken in EXEC_BACKEND case */
107  }
108  else
109  {
110  int i;
111 
112  /*
113  * Initialize all the buffer headers.
114  */
115  for (i = 0; i < NBuffers; i++)
116  {
118 
119  CLEAR_BUFFERTAG(buf->tag);
120 
121  pg_atomic_init_u32(&buf->state, 0);
122  buf->wait_backend_pgprocno = INVALID_PGPROCNO;
123 
124  buf->buf_id = i;
125 
126  /*
127  * Initially link all the buffers together as unused. Subsequent
128  * management of this list is done by freelist.c.
129  */
130  buf->freeNext = i + 1;
131 
134 
136  }
137 
138  /* Correct last entry of linked list */
140  }
141 
142  /* Init other shared buffer-management stuff */
143  StrategyInitialize(!foundDescs);
144 
145  /* Initialize per-backend file flush context */
148 }
149 
150 /*
151  * BufferShmemSize
152  *
153  * compute the size of shared memory for the buffer pool including
154  * data pages, buffer descriptors, hash tables, etc.
155  */
156 Size
158 {
159  Size size = 0;
160 
161  /* size of buffer descriptors */
162  size = add_size(size, mul_size(NBuffers, sizeof(BufferDescPadded)));
163  /* to allow aligning buffer descriptors */
164  size = add_size(size, PG_CACHE_LINE_SIZE);
165 
166  /* size of data pages */
167  size = add_size(size, mul_size(NBuffers, BLCKSZ));
168 
169  /* size of stuff controlled by freelist.c */
170  size = add_size(size, StrategyShmemSize());
171 
172  /* size of I/O condition variables */
173  size = add_size(size, mul_size(NBuffers,
175  /* to allow aligning the above */
176  size = add_size(size, PG_CACHE_LINE_SIZE);
177 
178  /* size of checkpoint sort array in bufmgr.c */
179  size = add_size(size, mul_size(NBuffers, sizeof(CkptSortItem)));
180 
181  return size;
182 }
static void pg_atomic_init_u32(volatile pg_atomic_uint32 *ptr, uint32 val)
Definition: atomics.h:223
Size BufferShmemSize(void)
Definition: buf_init.c:157
CkptSortItem * CkptBufferIds
Definition: buf_init.c:25
char * BufferBlocks
Definition: buf_init.c:22
WritebackContext BackendWritebackContext
Definition: buf_init.c:24
void InitBufferPool(void)
Definition: buf_init.c:68
ConditionVariableMinimallyPadded * BufferIOCVArray
Definition: buf_init.c:23
BufferDescPadded * BufferDescriptors
Definition: buf_init.c:21
#define GetBufferDescriptor(id)
#define BufferDescriptorGetContentLock(bdesc)
#define FREENEXT_END_OF_LIST
#define BufferDescriptorGetIOCV(bdesc)
#define CLEAR_BUFFERTAG(a)
Definition: buf_internals.h:97
void WritebackContextInit(WritebackContext *context, int *max_pending)
Definition: bufmgr.c:4871
int backend_flush_after
Definition: bufmgr.c:160
size_t Size
Definition: c.h:540
void ConditionVariableInit(ConditionVariable *cv)
void StrategyInitialize(bool init)
Definition: freelist.c:474
Size StrategyShmemSize(void)
Definition: freelist.c:453
int NBuffers
Definition: globals.c:136
int i
Definition: isn.c:73
Assert(fmt[strlen(fmt) - 1] !='\n')
void LWLockInitialize(LWLock *lock, int tranche_id)
Definition: lwlock.c:734
@ LWTRANCHE_BUFFER_CONTENT
Definition: lwlock.h:177
#define PG_CACHE_LINE_SIZE
static char * buf
Definition: pg_test_fsync.c:67
#define INVALID_PGPROCNO
Definition: proc.h:83
Size add_size(Size s1, Size s2)
Definition: shmem.c:502
void * ShmemInitStruct(const char *name, Size size, bool *foundPtr)
Definition: shmem.c:396
Size mul_size(Size s1, Size s2)
Definition: shmem.c:519